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FOOD COMPOSITION AND ADDITIVES
Improvement of AOAC Official Method 984.27 for theDetermination of Nine Nutritional Elements in Food Products byInductively Coupled Plasma-Atomic Emission Spectroscopy After
Microwave Digestion: Single-Laboratory Validation and Ring Trial
ERIC POITEVIN, MARINE NICOLAS, LAETITIA GRAVELEAU, JANIQUE R ICHOZ, DANIEL ANDREY, and FLORENCE MONARD
Nestlé Research Center, Vers-Chez-Les-Blanc, CH-1000 Lausanne 26, Switzerland
Collaborators: A. Abrahamson; A. Baillon; J. Barrios; S. Berger; R. Berrocal; R. Bos; L. Brullebaut; C. Caseiro; L.F. Choo;
G. Cole; G. Daix; C. Dekussche; G.-S. Dhillon; A. Fortineau; C. Gaudin; M.J. Gonzales; R. Leal; R.O. Mabiog; T. Noorlos;
R. Reba; C. Senechal
A single-laboratory validation (SLV) and a ring trial
(RT) were undertaken to determine nine nutritional
elements in food products by inductively coupledplasma-atomic emission spectroscopy in order to
improve and update AOAC Official Method 984.27.
The improvements involved optimized microwave
digestion, selected analytical lines, internal
standardization, and ion buffering. Simultaneous
determination of nine elements (calcium, copper,
iron, potassium, magnesium, manganese, sodium,
phosphorus, and zinc) was made in food products.
Sample digestion was performed through wet
digestion of food samples by microwave
technology with either closed or open vessel
systems. Validation was performed to characterize
the method for selectivity, sensitivity, linearity,
accuracy, precision, recovery, ruggedness, and
uncertainty. The robustness and efficiency of this
method was proved through a successful internal
RT using experienced food industry laboratories.
Performance characteristics are reported for
13 certified and in-house reference materials,
populating the AOAC triangle food sectors, which
fulfilled AOAC criteria and recommendations for
accuracy (trueness, recovery, and z -scores) and
precision (repeatability and reproducibility RSD
and HorRat values) regarding SLV and RT. This
multielemental method is cost-efficient,time-saving, accurate, and fit-for-purpose
according to ISO 17025 Norm and AOAC
acceptability criteria, and is proposed as an
improved version of AOAC Official Method 984.27
for fortified food products, including infant
formula.
R
obust and efficient methods with well-characterized
reference materials are needed by food-testing and
nutrition laboratories to facilitate compliance with
nutritional labeling laws and claim requirements, to provide
traceability for food exports needed for acceptance in many
foreign markets, and to improve the accuracy of nutrition
information that is provided to assist consumers in making
sound dietary choices (1, 2). Inductively coupled plasma-
atomic emission spectroscopy (ICP-AES) is one of the most
commonly used techniques within the food industry for
accurate and cost-efficient routine analyses of nutritional
minerals in food products, plants, pet food, raw materials, and
feeding stuffs (3–15).
AOAC Method 984.27 was validated 25 years ago via a
collaborative study in which acid digestion withHNO3/HClO4 and ICP-AES analysis with radial grating
configuration were used to determine nine nutritional
minerals in infant formula (16). Standard procedures for the
decomposition of food samples usually involve dry-ashing in
a muffle furnace or wet digestion with combined
acids (6, 10, 17). Compared to the classical digestion
procedures, microwave digestion has some significant
advantages with respect to speed of analysis, analyte loss,
sample contamination, and safe acid handling during sample
preparation (8). The use of microwave digestion before
ICP-AES analysis provides an accurate method for the
determination of nutritional minerals targeted for labeling of
food products (5).
The objective of this study is to improve AOAC Method
984.27 in terms of sample preparation time and throughput
using microwave digestion, and analytical performance using
the latest generation of ICP-AES equipment under robust
conditions (18), internal standardization (19, 20), and ion
buffer (21) to correct for physical and chemical interferences,
to compensate for matrix effects (22–25) induced by the
complexity of the food samples, and to improve short-term
accuracy (repeatability) and long-term stability (reproducibility
and calibration curve validity in a long analysis batch.
1484 POITEVIN ET AL.: JOURNAL OF AOAC I NTERNATIONAL VOL. 92, NO. 5, 2009
Received April 30, 2009. Accepted by SG June 19, 2009.Corresponding author’s e-mail: eric.poitevin@rdls.nestle.com
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The validation of this method involved a single-laboratory
validation (SLV), a ruggedness study, and a ring trial (RT) in
accordance with ISO 17025 and AOAC guidelines (26):
(a) SLV .—Performed using ICP-AES with axial grating
after a closed-vessel microwave digestion, on 10 in-house and
certified reference materials.
(b) Ruggedness study.—Performed in parallel, analyzing
with and without ionization buffer, the spiking elements ineight food-grade salts and testing six in-house and certified
reference materials in repeatability and reproducibility
conditions with different ICP-AES equipment (axial, radial,
and dual-view grating configurations) after open- and
closed-vessel microwave-based digestions.
(c) RT. —Involving nine laboratories was organized to
analyze five in-house and certified reference materials.
Thirteen well-characterized reference materials were
selected to populate the AOAC triangle, in which foods could
be categorized into nine sectors based on their fat, protein, and
carbohxdrate contents (27). All the results obtained on
reference materials have been treated with robust
statistics (28, 29) to verify that the updated procedure is
fit-for-purpose in terms of specificity, sensitivity, linearity,
trueness, and precision; and can be proposed as an improved
version of officialAOAC Method 984.27 regardingmicrowave
digestion, internal standardization, and ion buffering.
Experimental
Apparatus
(a) Closed-vessel microwave digestion systems.—A CEM
Mars Xpress (CEM, Matthews, NC) was used for the SLV,
including ruggedness test MD1 (Table 1). Other microwave
systems from CEM and Milestone (Shelton, CT) suppliers
were used for ruggedness tests MD2, MD3, and MD4 and for
the collaborative study RT (Table 1).
(b) Open-vessel microwave digestion system.—A CEM
MDS 2000 was used for test MD2 and by one laboratory for
the RT.
(c) ICP-AES spectrometers.—A Varian Vista-Pro axialICP-AES instrument with SPS-5 autosampler (Varian Inc.,
Mulgrave, Victoria, Australia) was used for the SLV,
including tests MD1 and MD2. Other ICP-AES spectrometers
from Perkin Elmer (Norwalk, CT), Varian, and Spectro
(Kleve, Germany) were used for the MD3 and MD4 tests and
for the RT.
(d) Balance.—A balance (AT 200, Mettler-Toledo, Inc.,
Greifensee, Switzerland) with readability of 0.1 mg (SLV, tests
MD1 and MD2) or equivalent (tests MD3, MD4, and RT).
(e) Sub-boiling quartz distillation apparatus for acids.—A
Kürner Analysentechnik (Rosenheim, Germany) distillator
(SLV, MD1, and MD2) for purifying acids or equivalent (tests
MD3, MD4, and RT).(f ) Fumehood .—A fumehood acid-resistant was used
(SLV, tests MD1 and MD2) or equivalent (tests MD3, MD4,
and RT).
(g) Drying oven.—A Heraeus drying oven 6120T
(Heraeus, Hanau, Germany) was used for the SLV, and tests
MD1 and MD2, and similar equipment was used for tests
MD3, MD4, and RT.
(h) Mixer or grinder for homogenization.—A Retsch
(Haan, Germany) mixer GM200 was used for the SLV, tests
MD1 and MD2, or equivalent (tests MD3, MD4, and RT).
POITEVIN ET AL.: JOURNAL OF AOAC I NTERNATIONAL VOL. 92, NO. 5, 2009 1485
Table 1. Microwave digestion systems (MD1, MD2, MD3, MD4) and ICP-AES equipment used for single-laboratory
validation and ring trial
Test codea Digestion modeb Digestion equipment Nebulizer/chamber ICP equipment Grating configuration
SLV MDC CEM Mars Xpress Concentric/cyclonic Varian Vista Pro AX Axial view
MD1 MDC CEM Mars Xpress Concentric/cyclonic Varian Vista Pro AX Axial view
MD2 MDO CEM MDS 2000 Concentric/cyclonic Varian Vista Pro AX Axial view
MD3 MDC Milestone MLS Ethos Concentric/cyclonic Spectro Ciros Radial view
MD4 MDC Milestone MLS 1200 Concentric/cyclonic Perkin Elmer Optima 5300 DV Dual view
RT MDC CEM Mars Xpress Concentric/cyclonic Perkin Elmer Optima 5300 DV Dual view
RT MDC CEM Mars 5 Concentric/cyclonic Perkin Elmer Optima 2000 DV Dual view
RT MDC CEM Mars Xpress Concentric/cyclonic Varian 720 ES Axial view
RT MDC CEM Mars Xpress Crossflow/scott Perkin Elmer Optima 3300 RL Radial view
RT MDO CEM MDS 2000 Crossflow/scott Perkin Elmer Optima 4300 DV Dual view
RT MDC CEM Mars Xpress Concentric/cyclonic Varian 720 ES Axial view
RT MDC CEM Mars Xpress Concentric/cyclonic Perkin Elmer Optima 2100 DV Dual view
RT MDC CEM Mars Xpress Concentric/cyclonic Perkin Elmer Optima 5300 DV Dual view
RT MDC CEM Mars Xpress Concentric/cyclonic Perkin Elmer Optima 2100 DV Dual view
a SLV = Single-laboratory validation; MD = ruggedness test using different microwave digestion systems and ICP-AES equipment; RT = ringtrial.
b MDC = Closed-vessel microwave digestion system; MDO = open-vessel microwave digestion system.
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Materials
(a) Volumetric flasks.—Glass, 50, 100, 500, 1000 mL
(SLV, tests MD1 and MD2) or equivalent (tests MD3, MD4,
and RT).
(b) Erlenmeyer flask for slurry preparation.—Glass,
100mL (SLV, tests MD1 andMD2) or equivalent (tests MD3,
MD4, and RT).
(c) Sample tubes.—Polyethylene or polystyrene, tubes 15
or 50 mL with caps (Falcon) for ICP analysis (SLV, tests
MD1 and MD2) or equivalent (tests MD3, MD4, and RT).
(d) Filters.—Ashless filter papers, quantitative (SLV,
tests MD1 and MD2), Whatman 589/1 (diameter 125 mm
and/or 90 mm; Schleicher & Schuell, Whatman, Dassel,Germany), or equivalent (tests MD3, MD4, and RT).
(e) Pipets.—Macropipet, variable volume 0.5–5.0 mL;
micropipet, variable volume 50–200 L and 200–1000 L;
electronic digital pipet 50–1000 L (SLV, tests MD1 and
MD2), or equivalent (tests MD3, MD4, and RT).
(f ) Samples.—Certified and standard reference materials
from National Institute of Standards and Technology (NIST;
Gaithersburg, MD) and National Metrology Institute (LGC
standards, Teddington, UK), in-house reference available
samples (from internal proficiency tests), and raw materials
(Table 2) were used for the SLV, ruggedness tests MD1,MD2, MD3, and MD4 and internal RT, including dairy-based
products, milk, and cereals-based products, chocolate and
dietetic milk powders, refrigerated meals, pet food, and raw
materials, such as whole egg powder, wheat gluten, corn bran,
and added food-grade salts (calcium carbonate, calcium
phosphate tribasic, calcium citrate tribasic, potassium
chloride, magnesium carbonate, magnesium chloride,
manganese sulfate, and sodium chloride).
Chemicals and Reference Solutions
(a) High grade water, H 2O (18 M ).—MilliQ™ Plus
system (Millipore, Bedford, MA).(b) Nitric acid (HNO3 ).—65% (w/v), Suprapure.
(c) Nitric acid (HNO3 ).—65% (w/v), analytical grade.
(d) Hydrochloric acid .—37% (w/v), analytical grade.
(e) Hydrogen peroxide.— 97% (w/v), analytical grade.
(f ) Multistandard.— CPI International (Santa Rosa, CA).
Composition of the CPI standard solution, in mg/L: Ca =
7500; Cu = 50; Fe = 250; K = 10 000; Mg = 2500; Mn = 1.25;
Na = 5000; P = 5000; Zn = 100.
(g) Calcium standard solution.— 10 000 mg/L (Merck,
Darmstadt, Germany).
1486 POITEVIN ET AL.: JOURNAL OF AOAC I NTERNATIONAL VOL. 92, NO. 5, 2009
Table 2. Raw materials, certified, and in-house reference materials used for SLV and RT
Material type Sample reference AOAC food triangle sector a Test code
Sterilized cream LGC RM 7104 1 SLV
Baking chocolate NIST SRM 2384 2 SLV
Peanut butter NIST SRM 2387 3 RT
Whole egg powder NIST RM 8415 4 SLV
Chocolate milk powder CMP 5 SLVb - RT
Infant cereals IC 5 SLVb - RT
Baby food composite NIST SRM 2383 5 SLV
Corn bran NIST RM 8433 5 SLVb
Dietetic milk powder 1 DMP1 6 SLVb
Dietetic milk powder 2 DMP2 6 RT
Pet food PET 6 SLVb
Nonfat milk powder NIST SRM 1549 7 SLVb
Wheat gluten NIST RM 8418 9 RT
Calcium carbonate CAS No. 471-34-1 NAc
SLV
Calcium phosphate tribasic CAS No. 7758-84-4 NA SLV
Calcium citrate tribasic CAS No. 5785-44-4 NA SLV
Potassium chloride CAS No. 7447-40-7 NA SLV
Magnesium carbonate CAS No. 546-93-0 NA SLV
Magnesium chloride CAS No. 7791-18-6 NA SLV
Manganese sulfate CAS No. 10034-96-5 NA SLV
Sodium chloride CAS No. 7647-14-5 NA SLV
a Sector number (1 to 9) of the food triangle (27).b SLV, including ruggedness tests (MD).c NA = Not applicable.
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(h) Potassium standard solution.—10 000 mg/L (Merck).
(i) Sodium standard solution.—10 000 mg/L (Merck).
( j) Magnesiumstandard solution.—10 000 mg/L (Merck).
(k ) Phosphorus standard solution.—10 000 mg/L (Merck).
(l) Iron standard solution.—1000 mg/L (Merck).
(m) Zinc standard solution —1000 mg/L (Merck).
(n) Copper standard solution.—1000 mg/L (Merck).
(o) Manganese standard solution.—1000 mg/L (Merck).
(p) Indium standard solution.—1000 mg/L (Merck).
(q) Chromium standard solution.—1000 mg/L (Merck).
(r) Strontium standard solution.—1000 mg/L (Merck).
(s) Yttrium standard solution.—1000 mg/L (Merck).
(t) Cesium chloride.—Analytical grade (Merck).
Preparation of Reagents and Standard Solutions
(a) Stock standard solution.—Working standards were
prepared from a CPI multistandard commercial stock standard
solution.
(b) Working standard solutions.—Standards prepared
from stock standard solution are designed to have the same
acid concentration as digested test solutions (i.e., 10% v/v
using sub-boiled or analytical grade HNO3 (SLV and MD1)
or 15% v/v (MD2) using combined acids (HNO3, H2O2, and
HCl). (1) Std6 .—Pipet 3.2 mL stock standard solution into a
100 mL acid-washed volumetric flask. Add 10 mL analytical
grade HNO3 (SLV, MD1) or 15 mL combined acids (MD2),
dilute to volume with H2O, mix, and transfer to acid-washed
polyethylene bottle. (2) Std5.—Pipet 1.6 mL stock standard
solution into a 100 mL acid-washed volumetric flask. Add
10 mL analytical grade HNO3 (SLV, MD1) or 15 mL
combined acids (MD2), dilute to volume with H2O, mix, and
transfer to acid-washed polyethylene bottle. (3) Std4.—Pipet
0.8 mL stock standard solution into a 100 mL acid-washed
volumetric flask. Add 10 mL analytical grade HNO3 (SLV,
MD1) or 15 mL combined acids (MD2), dilute to volume with
H2O, mix, and transfer to acid-washed polyethylene bottle.
(4) Std3.—Pipet0.4 mL stock standard solution into a 100 mL
acid-washed volumetric flask. Add 10 mL analytical grade
HNO3 (SLV, MD1) or 15 mL combined acids (MD2), dilute
to volume with H2O, mix, and transfer to acid-washed
polyethylene bottle. (5) Std2.—Pipet 0.2 mL stock standard
solution into a 100 mL acid-washed volumetric flask. Add
10 mL analytical grade HNO3 (SLV, MD1) or 15 mL
combined acids (MD2), dilute to volume with H2O, mix, and
transfer to acid-washed polyethylene bottle. (6 ) Std1.—Pipet
0.1 mL stock standard solution into a 100 mL acid-washed
volumetric flask. Add 10 mL analytical grade HNO3 (SLV,MD1) or 15 mL combined acids (MD2), dilute to volume with
H2O, mix, and transfer to acid-washed polyethylene bottle.
(7 ) Blank .—Add 10 mL analytical grade HNO3 (SLV, MD1)
or 15 mL combined acids (MD2) into a 100 mL acid-washed
volumetric flask, dilute to volume with H2O, mix, and transfer
to acid-washed polyethylene bottle. All calibration solutions
are stable for 1 week in glass volumetric flasks.
(c) Ionization buffer/internal standard solution for
automatic addition.—Weigh 12.67 g cesium chloride into a
1000 mL acid-washed volumetric flask [ Note: Ruggedness
tests.—Weigh 1.27 g cesium chloride. Cesium 0.1% (w/v)
solution was tested as the minimal recommended
concentration required for element analysis in most food
matrixes. Cs solution 1% (w/v) is recommended if an element
is present at low concentration in high-salted food raw
materials (e.g., culinary products or tastemakers) or if it is
analyzed as an impurity in food-grade salts. Add 40 mL
indium 1000 mg/L and 10 mL each of strontium, yttrium, and
chromium 1000 mg/L stock solutions, as internal standards.
Add 10 mL analytical grade HNO3. Dilute to volume with
H2O, mix, and transfer to an acid-washed polyethylene bottle.
( Note: Reagent concentrations assume the use of same pump
tubing internal diameter for both internal standard/ionization
POITEVIN ET AL.: JOURNAL OF AOAC I NTERNATIONAL VOL. 92, NO. 5, 2009 1487
Table 3. Open-vessel microwave digestion program
(CEM MDS 2000) used for MD2 ruggedness test
No. of samplesto digest Power a
Hold time, min(step 1)
Hold time, min(step 2)
5 23 20 10
6 27 20 10
7 31 20 108 35 20 10
9 39 20 10
10 43 20 10
11 47 20 10
12 51 20 10
a Power expressed in % of maximum power (600 watts for CEMMDS 2000 system).
Table 4. ICP-AES conditions (Varian Vista AX PRO) for
SLV, MD1, and MD2 ruggedness tests
Instrument Varian Vista Pro AX
RF generator 40 MHz
RF power 1100 W
Torch quartz injector id 2.5 mm
Argon flow rate Plasma 18 L/min
Auxiliary 2.25 L/min
Nebulizer 0.8 L/min
Spray chamber
Cyclonic thermostated (water
cooled)
Nebulizer Microconcentric
Pump Peristaltic, 3 channels
Pump tubing id 0.64 mm
Sample flow rate 0.75 mL/min
Polychromator Echelle
Resolution 6.9 pm at Mo 202.032 nm
Detector Segmented CCD
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buffer and sample pump tubes (i.e., orange/white, 0.64 mm id)
using automatic addition.
Sample Preparation and Digestion
(a) Test sample preparation.—Homogenize the test
sample (e.g., serving size or declared labeled size) by either
grinding as fine as possible using a mixer to obtain a fine
powder and/or by preparing a slurry with H2O: weigh 10
± 0.1 g test sample, and put into a 100 mL Erlenmeyer flask;
add 90 ± 0.1 g H2O, and mix well with stopper ( Note: Water
can be preheated at 50C for a better homogenization of samples, e.g., infant cereals and fortified milk powders).
(b) Test portion preparation for closed-vessel microwave
digestion (SLV, MD1, MD3, and MD4 ruggedness
tests).—Accurately weigh 0.50 ± 0.01 g test portion (or
sample mass in the prepared slurry) into digestion vessel. Use
either weighing paper insert to line the vessel walls or Pasteur
pipet during sample transfer to keep sample from adhering to
sides of vessel. Fluid samples or test portion from slurry test
sample may be weighed directly after mixing. Add 5.0 ±
0.1 mL analytical grade HNO3, loosely cap vessels without
sealing, and predigest at room temperature until vigorous
foaming subsides. Close vessels and place in CEM Mars
Xpress microwave or in other closed-vessel microwave
systems.
(c) Test portion preparation for open-vessel microwave
digestion (MD2 ruggedness test).—Accurately weigh 1.0 ±
0.01 g test portion (orsample mass in theslurry) into a 100mL
volumetric flask. Carefully add 5 mL HNO3 and then 5 mL
H2O2. Allow the sample to stand for at least 10 min at roomtemperature. Distribute the volumetric flasks onto the
open-vessel microwave carousel to ensure homogeneous
microwave power application on all samples.
(d) Sample digestion for closed-vessel microwave
digestion (SLV, MD1, MD3, and MD4 ruggedness
tests).—Digest sample according to a ramp program as
follows: Conditions: Stage 1.—Power, expressed as
maximum power (1600 watts for CEM Mars Xpress system)
= 75%; ramp time, 5 min; 120C; hold time, 5 min.
Stage 2.—Power, 75%; ramp time, 5 min; 200C; hold time,
25 min. Then cool vessels, vent, and transfer digests to 50 mL
volumetric flasks, dilute to volume with H2O, and mix. A
digestion is judged complete when clear-to-yellow analytical
solutions are produced. Filter the digested solution using an
ashless filter paper for turbid samples containing fat,
discarding the first 20 mL of filtrate and collecting the
remaining filtrate for analysis. [ Note: Membrane disc filters
(0.45 m) are not recommended as they are generally not
metal free.] Transfer to polyethylene containers within 2 h.
Dilute with H2O the samples that are found to be above the
standard curve range, or have total content of minerals higher
than 1000 mg/L. Final dilutions require addition of
appropriate amounts of HNO3 to maintain the proportion of
10% (v/v) HNO3 in the final solution to be analyzed.
(e) Sample digestion for open-vessel microwave digestion(MD2 ruggedness test).—Digest sample according to an
appropriate power program close to that described in Table 3
for a CEM MDS 2000 system depending on the number of
distributed flasks. This first step requires 20 min heating time.
Yellow vapors will be emitted during the hydrolysis.
Carefully remove the flasks from the microwave system.
Allow the flasks to cool to room temperature and add 5 mL
HCl 35% (w/v). Heat the flasks for an additional 10 min using
the same program in the microwave system. Allow the flasks
to cool to room temperature. Transfer digests to 100 mL
volumetric flasks, dilute to volume with H2O, and mix. Filter
and prepare the digested solution before analysis as described
for closed-vessel microwave digestion in (d) but maintain the proportion of 15% (v/v) combined acids in the final solution
to be analyzed.
(f ) Digestion vessel decontamination for closed-vessel
microwave digestion (SLV, MD1, MD3, and MD4 ruggedness
tests). —Conditions: Step 1.—Power, express in % of
maximum power (1600 watts for CEM Mars Xpress system)
= 75%; ramp time, 5 min; 180C; hold time, 5 min.
Decontaminate used digestion vessels with 5 mL HNO3 for a
CEM Mars Xpress system and rinse with H2O. Dry vessels at
60C in drying oven for 1 h.
1488 POITEVIN ET AL.: JOURNAL OF AOAC I NTERNATIONAL VOL. 92, NO. 5, 2009
Table 5. Recommended and alternate ICP analytical
lines used for SLV and RT
Element lines, nm Internal standard lines, nm
Ca IIa
317.933 In I 303.936
Ca IIb
317.933 Y II 371.028
Cu Ia
324.754 In I 303.936
Cu Ib 324.754 Y II 371.028
Cu Ib
327.395 In I 303.936
Cu Ib
327.395 Y II 371.028
Fe IIa
259.94 Sr II 338.071
Fe IIb
259.94 Y II 371.028
Fe IIb
259.94 Cr II 283.563
K Ia
766.491 Sr I 460.733
Mg Ia
285.213 In I 303.936
Mg Ib
285.213 Y II 371.028
Mg IIa
279.078 In I 303.936
Mn IIb
257.61 Sr II 338.071
Mn IIb 257.61 Sr I 460.733
Mn IIb
257.61 Y II 371.028
Na Ia
589.592 Sr I 460.733
P Ia
213.618 In I 303.936
P Ib
178.222 Sr I 460.733
P Ib
178.222 Y II 371.028
Zn Ia
213.857 Sr II 338.071
Zn Ib
213.857 Sr I 460.733
Zn Ib
213.857 Y II 371.028
a Recommended lines for ICP-AES analysis.b Alternate confirmatory lines for ICP-AES analysis.
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(g) Digestion vessel decontamination for open-vessel
microwave digestion (MD2 ruggedness test).—The glass
volumetric flasks can be directly used after being washed in a
laboratory washing machine or soaked overnight in a water
bath with HNO3 30% (v/v) and rinsed with H2O to avoid or
minimize risk of iron contamination.
(h) Spiked food grade salt preparation (SLV).—Weigh
0.2 ± 0.01 g food-grade salt into a 100 mL volumetric flask.
Add deionized water and 10 mL HNO3. Add 0.8 mL stock
standard solution corresponding to standard Std4 [prepared
from CPI commercial solution (Ca, 60 mg/L; Cu, 0.4 mg/L;
Fe, 2 mg/L; K, 80 mg/L; Mg, 20 mg/L; Mn, 0.01 mg/L; Na,40 mg/L; P, 40 mg/L; Zn, 0.8 mg/L)]. Dissolve salt and dilute
to volume with deionized water.
ICP Analysis
(a) ICP-AES spectrometer (SLV-MD1 and MD2
ruggedness tests).—A Varian Vista-Pro axial ICP-AES
instrument with autosampler SP5 was used during SLV, using
the operating conditions shown in Table 4. The recommended
and alternative analytical lines (nm) used for elements to be
determined and internal standards (IS) are shown in Table 5.
A 3-channel peristaltic pump (Gilson, Middleton, WI) and a T
connector (id 1.5 mm/Socochim, Lausanne, Switzerland)
linked between the peristaltic pump and nebulizer were used
to avoid having to manually add ionization buffer and IS to
each sample solution. A thermostatted (15C) cyclonic spray
chamber (Jacketed ‘Althea’ Cyclonic Glass Spray Chamber,
water-cooled, EPOND SA, Vevey, Switzerland) equipped
with a micro-concentric nebulizer [C-Type ‘Caliber’ standard
Concentric Glass Nebulizer with ‘NebLink’ sample capillary
tube and argon connector (EPOND)] were used to obtain the
best method performance. Sample and IS pump tubes (e.g.,
orange/white, 0.64 mm id Socochim), and peristaltic pumprotation speed (15 rpm), were selected to keep sample and IS
pump tubes of similar size to maximize mixing accuracy,
while maintaining the required detection levels. Ionization
buffer (cesium chloride) was combined with IS solution to
compensate for easy ionizable element (EIE) effects (e.g., K,
Na, and Ca) in the plasma, because certain food materials can
contain substantial concentrations of these elements that
provide a significant source of electrons in the plasma. The
presence of ionization buffer in all samples and standards will
minimize the effects of varying concentrations of EIEs in the
POITEVIN ET AL.: JOURNAL OF AOAC I NTERNATIONAL VOL. 92, NO. 5, 2009 1489
Table 6. Recovery and SD values found for nine elements using recommended lines after optimization of CEM Mars
Xpress microwave digestion of two Standard Reference Materials (NIST SRM 2384, NIST SRM 2383) and one
Reference Material (NIST RM 8415)
Concentration, mg/kg
ElementBaking chocolate(NIST SRM 2384)
Whole egg powder (NIST RM 8415)
Baby food composite(NIST SRM 2383)
Calcium Certified
a
840 ± 74 2480 ± 190 853 ± 28Found
b(recovery, %)
c 793 ± 100 (94) 2627 ± 358 (106) 868 ± 12 (102)
Copper Certifieda 23.2 ± 1.2 2.70 ± 0.35 1.42 ± 0.12
Foundb (recovery, %)c 24.1 ± 0.2 (104) 2.90 ± 0.05 (107) 1.77 ± 0.22 (125)
Iron Certifieda 132.0 ± 1.1 112 ± 16 8.44 ± 0.44
Foundb (recovery, %)c 129.6 ± 1.2 (98) 105 ± 0.3 (94) 10.41 ± 1.11 (123)
Potassium Certifieda 8200 ± 500 3190 ± 370 3600 ± 100
Foundb
(recovery, %)c
7750 ± 100 (95) 3125 ± 27 (98) 3793 ± 33 (105)
Magnesium Certifieda 2570 ± 150 305 ± 27 248 ± 5
Foundb (recovery, %)c 2567 ± 34 (100) 292 ± 1 (96) 245 ± 3 (99)
Manganese Certifieda 20.3 ± 1.3 1.78 ± 0.38 1.39 ± 0.11
Foundb
(recovery, %)c
19.9 ± 0.1 (98) 1.62 ± 0.01 (91) 1.42 ± 0.002 (102)Sodium Certifieda 40 ± 4 3770 ± 340 390 ± 28
Foundb
(recovery, %)c
NDd
3550 ± 222 (94) 378 ± 7 (97)
Phosphorus Certifieda 3330 ± 210 10010 ± 320 948 ± 33
Foundb (recovery, %)c 3301 ± 48 (99) 11643 ± 295 (116) 962 ± 10 (101)
Zinc Certifieda 36.6 ± 1.7 67.5 ± 7.6 10.5 ± 0.3
Foundb (recovery, %)c 35 ± 0.5 (96) 60.9 ± 0.1 (90) 10.6 ± 0.03 (101)
a Uncertainty expressed either as a 95% confidence interval or as an interval based on the entire range of accepted results for a singledetermination.
b SD from average of triplicates analysis.c Found value/certified value ratio expressed in %.d ND = Not determined (<LOQ).
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sample. Power settings and nebulizer gas flow were optimized
to ensure that the Mg 280.271:Mg 285.213 ratio demonstrates
robust operating conditions (18) in accordance with the ratio
established by the instrument manufacturer. Five replicate
readings of the same sample were performed, with relatively
long integration times to minimize noise. The solution
presented to the nebulizer contains at the most 5000 mg/L
cesium ( Note: 500 mg/L Cs for ruggedness tests MD1, MD2);
20 mg/L indium; and 5 mg/L strontium, yttrium, and
chromium; less than half of each element concentration of the
higher working standard Std6 and <0.5 g/L total dissolved
minerals. All responses for both recommended and alternative
lines for each element are corrected using one IS line
(Table 5).
(b) ICP-AES spectrometers (MD3 and MD4 ruggedness
tests).—Operating conditions of both instruments (Table 1) as
well as sample and IS pump tubes and peristaltic pump
rotation speed used were selected according to manufacturer’s
recommendations and were adapted to optimize aerosol and
maximize precision, and to demonstrate robust operating
conditions. They were capable of determining at least the
recommended multiple lines for each element of interest
(Table 5). Combined ionization buffer/IS solution was
prepared such that after mixing digest sample and
IS/ionization buffer solutions using the instrument’s peristaltic pump, the combined solution presented to the
nebulizer contained at least 500 mg/L Cs; 20 mg/L indium;
5 mg/L strontium, yttrium, and chromium; and less than half
of each element concentration of the higher working standard
and <.5 g/L total dissolved minerals. All sample instrument
responses of recommended and alternate lines for each
element are corrected using one IS line (Table 5).
(c) Quantification.—The concentration (C) of each
element, in mg/kg, was calculated as follows:
C a V
m
F
where C = concentration in the test portion sample (mg/kg); a
= concentration (mg/L) of the element in the digest solution; V
= volume (mL) of the test solution after being made up [i.e.,
50 mL for closed vessel microwave digestion (MDC) for SLV
and 100 mL for open-vessel microwave digestion (MDO)
used for test MD2]; F = dilution factor of the test solution; m =
weight of the test portion (g).
Statisic Calculations
All data used for selectivity, accuracy and precision
performance tests were treated using robust statistics (29)
based in the concept of Rousseeuw and Croux (28). The
presence of some suspect values (outliers) can strongly distort
classical estimations. However, results must not be eliminated
without a valid justification. For that reason, robust statistics,
which provide good estimations even without the elimination
of suspect values, have been used in the SLV and RT. These
robust estimations are insensitive to extreme values and
depend only slightly on data distribution. It is then neither
necessary to test for outliers nor to exclude suspect values.
The median has been used as a robust estimation of the central
value. The robust standard deviation SD(Sn) drawn from the
algorithm Sn of Rousseeuwand Croux (28) has been used as a
robust estimation of spread. This algorithm uses median
absolute distances between all the couples we can set up withthe data:
Sn = medi {medj *xi – xj *}
SD(Sn) = 1.1926 Sn
Statistical comparative t -test is the robust adaptation of the
classical t -test by replacing the mean with the median, and the
SD with the robust SD(Sn). Robust t -test was used for
selectivity (median comparison) and accuracy was evaluated
to check if the recovery is significantly different from 100%
(at 95 and 99% confidence intervals).
1490 POITEVIN ET AL.: JOURNAL OF AOAC I NTERNATIONAL VOL. 92, NO. 5, 2009
Table 7. Regression coefficients obtained from
weighed linear and nonlinear regression for
recommended and alternate lines
Calibration curvea Concn range, mg/L
Element line R² nonlinear b R² linear c Low High
Ca IId
0.99997 0.99980 0 240
Cu Id 0.99999 1.00000 0 2.1
Fe IId
0.99997 0.99999 0 8.5
K Id
0.99924 0.99326 0 320
Mg Id
0.99999 0.99891 0 75
Mn IId
1.00000 0.99998 0 0.04
Na Id
0.99996 0.99666 0 160
P Id
0.99998 0.99997 0 160
Zn Id
0.99999 0.99998 0 3.2
Ca IIe
0.99994 0.99993 0 240
Cu Ie
1.00000 0.99995 0 2.1
Cu Ie
0.99999 0.99999 0 2.1
Cu Ie 0.99999 0.99998 0 2.1
Fe IIe
0.99996 0.99997 0 8.5
Fe IIe
0.99999 0.99998 0 8.5
Mg Ie
0.99997 0.99929 0 80
Mg IIe
1.00000 0.99999 0 80
Mn IIe
1.00000 0.99997 0 0.04
Mn IIe
1.00000 0.99998 0 0.04
P Ie
0.99999 0.99967 0 160
P Ie
1.00000 0.99993 0 160
Zn Ie
0.99999 0.99991 0 3.2
Zn Ie
1.00000 1.00000 0 3.2
a Calibration with six standard solutions and a blank.b Weighed second degree quadratic regression.c Weighed linear regression without forcing zero.d Recommended lines for ICP-AES analysis.e Alternate confirmatory lines for ICP-AES analysis.
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Recovery is judged satisfactory if it is not significantly
different from 100% at 95% confidence interval ( P -value
>0.05) between the median concentration and the certified or
reference values (Table 2). Recovery is judged questionable if
it is not significantly different from 100% at 99% confidence
interval (0.01 < P -value < 0.05) between the median
concentration and the certified or reference values (Table 2).
Recovery is judged unsatisfactory if it is significantly
different from 100% at 99% confidence interval ( P -value
<0.01) between the median concentration and the certified or
reference values (Table 2).
SLV
(a) Study material .—Ten materials included six reference
materials (RM) of LGC Promochem LGC RM 7104
(sterilized cream), of existing NIST Standard Reference
Material (SRM) NIST SRM 2384 (baking chocolate), NIST
RM 8415 (whole egg powder), NIST SRM 2383 (baby food
composite), NIST RM 8433 (corn bran), NIST SRM 1549
(nonfat milk powder), and four Nestlé well-characterized
reference samples of infant cereals with milk powder,
chocolate milk powder, dietetic milk powder (DMP1), and pet
food (PET). The reference values of element concentrations in
the four in-house reference materials and their associated
reproducibility SD were obtained from Nestlé proficiency
tests performed by a significant number of internal and
external laboratories (between 12 and 45 laboratories,
depending on element and materials analyzed) using robust
statistics (28).
(b) Microwave digestion optimization.—Main reagents
for microwave-assisted digestion are HNO3 and HCl. H2O2 is
generally used to remove any remaining organic residues of
rich-fat or rich-carbohydrate samples. MDC systems supplied
by manufacturers typically apply to a single food matrix or
minimize the analytical portion mass to account for the most
reactive food matrix. This approach is notefficient when a full
range of food matrixes is analyzed on a routine basis, and an
additional predigestion step is often used to allow various
matrixes to be digested concurrently. Thus, approach of a
single optimized MDC program for duty vessels with only
HNO3 operating up to 200C, which has been adapted on a
CEM Mars Xpress system, was favored: an optimal analytical
test portion mass of 0.5 g [based on an empirical maximum
energy release by the food of 3 kcal (8)] was used, and
concurrent digestions of triplicates of three NIST-certifiedRMs (baking chocolate, NIST SRM 2384; whole egg powder,
NIST RM 8415; and Baby Food Composite, NIST SRM
2383) were performed. Similar programs to that of CEM Mars
Xpress system were adapted on other MDC systems used for
MD3 and MD4 ruggedness tests. An optimized program for
MDO system CEM MDS 2000 (Table 3) was also developed
in parallel, and used for all matrixes during ruggedness test
MD2 and by one volunteer laboratory during the RT.
(c) Linearity.—A calibration curve was obtained from
seven standards, including a blank (Std0) and six
concentrations of the standard solution (Std1–Std6).
Weighted linear and quadratic regression analyses were
performed and correlation coefficient (R 2) values were
calculated.
(d) LOD and LOQ.—The instrumental detection (DL)
and quantification (QL) limits expressed in mg/L were
estimated using the SD approach by analyzing 10 replicates of
the low standard solution (Std1) according to the formula:
DL = 3 SD of the mean of Std1 determinations ( n = 10)
QL = 10 SD of the mean of Std1 determinations ( n = 10)
The DL and QL values of elements in real samples were
hence estimated assuming a sample weight of 0.5 g and a
dilution to 50 mL (i.e., a dilution factor of 100). Verification
of QL estimation was performed by checking satisfactory
performance characteristics (accuracy and precision) for
elements present in real matrixes at these estimated
concentrations, e.g., Ca, Cu, Fe, K, Na, P in corn bran (NIST
RM 8433), Mg, Zn in sterilized cream (LGC RM 7104), and
Mn in nonfat milk powder (NIST SRM 1549).
(e) Selectivity.—Element median recovery was calculated
using all the linesdisplayed in Table 5 from duplicates of eight
different solutions of spiked food grade salts (Table 2) with a
spiking concentration corresponding to Std4 prepared from
the CPI commercial solution. Robust t -test for comparison of
median recovery and SD (i.e., median of averages of
duplicates found per element using all analytical lines) of eachspiked element in all food-grade salts with and without
addition of ionization buffer Cs 1% (w/v) was performed.
(f ) Accuracy.—Three replicate test portions (r = 3) were
collected from each of seven (n = 7) different food samples
populating four of the nine food triangle sectors, and then
were digested and analyzed on 8 days (d = 8) corresponding to
nine series (i.e., 9 elements) of 168 data (n r d = 168).
Recovery median values (ratio of found and certified values)
and associated RSD were determined. Accuracy was
statistically evaluated.
POITEVIN ET AL.: JOURNAL OF AOAC I NTERNATIONAL VOL. 92, NO. 5, 2009 1491
Table 8. Estimated LOD and LOQ for the nine elements
in food matrixes obtained from recommended and
alternate element lines
Element LODa, mg/L LOQb, mg/L LOQc , mg/kg
Calcium 0.5 1.50 150
Copper 0.006 0.02 2
Iron 0.03 0.1 10Potassium 0.5 2 200
Magnesium 0.2 0.5 50
Manganese 0.0002 0.0005 0.05
Sodium 0.4 1 100
Phosphorus 0.4 1 100
Zinc 0.02 0.05 5
a Instrumental LOD calculated in solution.b Instrumental LOQ calculated in solution.c LOQ estimated in food matrixes (dilution factor 100).
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(g) Precision.—Both repeatability standard deviation
(SDr ; within day) and intermediate reproducibility standard
deviation (SDiR , between day) were determined.
(h) Uncertainty.—Uncertainty (U) was estimated using
the simplified approach based on existing validation data
proposed by Barwick and Ellison (30, 31), mainly from
precision and trueness studies, which, if properly planned to
cover as many of the uncertainty sources previously identifiedas possible, provide the necessary data required to calculate
measurement uncertainty. SDs of intermediate precision
(SDiR ) and recovery (SDrec) contributions are combined
together as followed to obtain the overall uncertainty (U):
U SD SDiR
2
rec 2
(i) HorRat values.—Horwitz ratio (HorRat value) was
calculated for SLV according to the equation:
HorRat value = RSD , %
2C , %
iR
0.1505
where RSDiR is the relative intermediate reproducibility
standard deviation of each element in each of the 10 tested,
certified or in-house reference matrixes; C is the relative
concentration (expressed as a dimensionless mass fraction) of
the analyte in question (valid for concentration ratioabove 10 –9).
The HorRat value is a simple performance parameter that
reflects the acceptability of a chemical method of analysis
with respect to precision (32).
HorRat value of 1.0 is judged satisfactory with limits of
acceptability of 0.3–1.5. Consistent deviations from the ratio
on the low side (values <0.3) may indicate unreported
averaging or excellent training and experience; consistent
deviations on the high side (values >1.5) may indicate
inhomogeneity of the test samples, need for further method
1492 POITEVIN ET AL.: JOURNAL OF AOAC I NTERNATIONAL VOL. 92, NO. 5, 2009
Table 9. Recovery values (%) and standard deviations (%) found using recommended lines for nine elements spiked
in eight food-grade salts
Spikedelementline
Calciumcarbonate
Calcium citratetribasic
Calciumphosphate
tribasicPotassium
chlorideMagnesiumcarbonate
Magnesiumchloride
Manganesesulfate Sodium chloride
Ca IIa
NDc ND ND 102.8 ±1.9 98.5 ± 0.3 102.1 ± 0.7 90.2 ± 5.6 102.8 ± 6.7
Ca IIb
ND ND ND 104.5 ± 2.1 100.6 ± 0.2 103.4 ± 0.6 98.2 ± 6.8 105.4 ± 6.7
Cu Ia 103.2 ± 0.5 100.4 ± 0.7 99.2 ± 1.2 105.0 ± 1.7 105.0 ± 0.4 105.1 ± 0.3 93.8 ± 5.6 105.3 ± 6.0
Cu Ib
106.8 ± 0.1 102.6 ± 0.5 102.5 ± 1.5 107.4 ± 1.9 107.0 ± 0.3 106.9 ± 0.3 102.3 ± 6.9 108.4 ± 6.0
Cu Ib
105.0 ± 0.6 102.4 ± 0.9 101.1 ± 1.5 106.9 ± 1.8 106.3 ± 0.5 107.0 ± 0.7 96.9 ± 5.6 106.6 ± 6.0
Cu Ib
108.7 ± 0.2 104.7 ± 0.7 104.5 ± 1.9 109.4 ± 2.0 108.0 ± 0.4 109.0 ± 0.7 105.5 ± 6.8 109.8 ± 6.0
Fe IIa
100.8 ± 0.5 96.6 ± 0.9 95.7 ± 2.2 104.5 ± 2.5 106.3 ± 1.7 104.8 ± 0.1 98.2 ± 6.2 105.3 ± 6.6
Fe IIb
99.6 ± 0.6 97.1 ± 0.9 96.0 ± 2.3 103.8 ± 2.5 102.5 ± 1.3 103.3 ± 0.1 96.9 ± 6.3 104.8 ± 6.4
Fe IIb
102.0 ± 0.3 99.0 ± 0.7 98.9 ± 2.2 104.5 ± 2.5 105.8 ± 1.2 104.6 ± 0.1 97.5 ± 5.9 105.7 ± 6.8
K Ia
105.3 ± 0.4 99.2 ± 0.9 98.1 ± 1.4 ND 109.1 ± 3.8 106.5 ± 0.8 102.5 ± 6.5 112.2 ± 7.7
Mg Ia
104.5 ± 0.1 101.3 ± 1.3 100.8 ± 2.5 107.4 ± 2.7 ND ND 94.3 ± 5.6 108.6 ± 7.4
Mg Ib
107.3 ± 0.3 102.7 ± 1.0 103.2 ± 2.9 109.0 ± 2.9 ND ND 102.3 ± 6.8 111.0 ± 7.4
Mg Ib
97.3 ± 0.6 96.4 ± 1.2 94.5 ± 2.1 101.2 ± 2.5 ND ND 88.4 ± 5.7 108.6 ± 7.4
Mn IIa
110.5 ± 8.9 98.0 ± 5.6 103.1 ± 1.1 110.2 ± 2.8 100.9 ± 18.7 103.9 ± 1.2 ND 107.8 ± 6.7
Mn IIb
107.7 ± 8.0 93.2 ± 5.6 106.1 ± 0.9 102.9 ± 2.4 100.4 ± 18.8 97.8 ± 0.6 ND 99.2 ± 6.2
Mn IIb
111.8 ± 8.0 99.6 ± 6.0 102.3 ± 1.2 109.0 ± 2.7 103.1 ± 17.0 102.1 ± 1.1 ND 106.7 ± 6.5
Na Ia
103.8 ± 1.0 99.7 ± 0.1 95.3 ± 0.6 106.5 ± 2.5 107.1 ± 1.3 107.9 ± 1.1 102.3 ± 7.1 ND
P Ia
100.7 ± 1.0 99.2 ± 1.3 ND 104.8 ± 1.9 99.2 ± 0.5 103.8 ± 1.0 90.5 ± 6.1 105.1 ± 6.8
P Ib
98.9 ± 1.0 96.2 ± 0.9 ND 102.2 ± 2.2 99.3 ± 1.0 104.1 ± 1.1 96.6 ± 6.8 101.6 ± 6.2
P Ib
105.6 ± 0.6 102.6 ± 1.0 ND 108.6 ± 2.2 102.0 ± 0.6 107.1 ± 0.9 100.2 ± 7.2 109.7 ± 6.6
Zn Ia
103.9 ± 0.3 101.6 ± 2.3 99.0 ± 1.3 107.4 ± 2.2 105.9 ± 0.3 115.0 ± 12.0 101.8 ± 6.9 108.3 ± 6.9
Zn Ib
97.0 ± 0.8 96.8 ± 2.4 91.3 ± 0.4 101.3 ± 2.2 98.6 ± 1.1 111.2 ± 11.3 97.5 ± 6.8 100.6 ± 6.5
Zn Ib
102.3 ± 0.3 101.8 ± 2.4 98.9 ± 1.4 106.2 ± 2.0 101.1 ± 0.5 113.0 ± 11.8 100.1 ± 7.0 107.4 ± 6.4
a Recommended lines for ICP-AES analysis.b Alternate confirmatory lines for ICP-AES analysis.c ND = Not determined.
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optimization or training, operating below the limit of
determination, or an unsatisfactory method. It is now one of
the acceptability criteria for many of the recently adopted
chemical methods analysis of AOAC INTERNATIONAL,
the European Union, and other European organizations
dealing with food analysis (33).
( j) Ruggedness.—Three replicate test portions (r = 3)were collected from each of the six (n = 6) different food
samples populating three of the nine food triangle sectors, and
then were digested using different closed-vessel (MD1, MD3,
and MD4) and open-vessel (MD2) microwave digestion
systems (Table 1). Triplicates were analyzed for 8 days (d = 8)
corresponding to nine series (i.e., nine elements) of 144 data
(n r d = 144), and using different ICP equipment with the
recommended lines (except the use of alternate 2MnII and2Zn I alternate lines for the MD4 test) according to adapted
ICP operating conditions used for SLV with addition of ion
buffer Cs 0.1% (w/v). Recovery median values, SDr (within
day), SDiR (between day), and HorRat values were
determined. Accuracy was statistically evaluated.
Ring Trial
(a) Design of the study.—Five materials that cover four of
the nine sectors of AOAC food triangle (Table 2) were
proposed for testing the proposed ICP-AES method for
determining the nine elements of interest in food matrixes
after microwave digestion through an internal RT.
(b) Study material .—Five materials were samples of
existing NIST SRM 2387 (peanut butter) and NIST RM 8418
(wheat gluten), and three in-house reference samples of infant
cereals with milk powder, chocolate milk powder, and dietetic
milk powder 2 (DMP2). The three in-house reference
materials were validated through Nestlé proficiency tests
performed by a significant number of internal and external
laboratories (between 12 and 45 depending on element and
materials analyzed). Their reference values and associated
SDR values were calculated using robust statistics (28).
(c) Protocol .—Three lots of each NIST material were
simply remixed in an amber container and sample portions of minimum 10 g were then extracted from random locations in
the container using a small weighing spatula and transferred
into numbered amber PVC 100 mL boxes (Greiner Bio-one,
Frickenhausen, Germany) for distribution to participants.
Sample portions of minimum 10 g were extracted from
random locations in each original P -test container of the
three in-house references using a small weighing spatula and
transferred into numbered amber PVC 100 mL boxes (Greiner
Bio-one) for distribution to participants. One set of five
numbered samples, including five amber 100 mL flasks
containing 10 g materials, was mailed to nine collaborators
who volunteered to participate in this study.
(d) Stock standard solution.—Prepare working standards
either from a multistandard commercial stock standard
solution (equivalent to that described for SLV, MD1, and
MD2 tests) or from an intermediate stock standard solution
previously prepared with ICP-grade individual element 1000
and 10 000 mg/L solutions.
(e) Intermediate stock standard solution.—(Composition
of the intermediate standard solution, in mg/L: Ca = 1500; Cu
=10;Fe=50;K=2000;Mg=500;Mn=0.25;Na=1000;P=
1000; Zn = 20.) Add into a 500 mL volumetric flask, 75 mL
calcium 10 000 mg/L, 5 mL copper 1000 mg/L, 25 mL iron
1000 mg/L, 100 mL potassium, 25 mL magnesium
10 000 mg/L, 0.125 mL manganese 1000 mg/L, 50 mLsodium 10 000 mg/L, 50 mL phosphorus 10 000 mg/L, and
10 mL zinc 1000 mg/L. Add 10 mL of analytical grade HNO3
and dilute to volume with H2O.
(f ) Working standard solutions.—Standards prepared
from intermediate stock standard solution are designed to
have the same acid concentration as digested test solutions.
(1) Std6 .—Pipet 15.0 mL intermediate standard solution into a
100 mL acid-washed volumetric flask. Add 10 mL analytical
grade HNO3, dilute to volume with H2O, mix, and transfer to
acid-washed polypropylene bottle. (2) Std5.—Pipet 10.0 mL
intermediate standard solution into a 100 mL acid-washed
volumetric flask. Add 10 mL analytical grade HNO3, dilute to
volume with H2O, mix, and transfer to acid-washed
polypropylene bottle. (3) Std4.—Pipet 5.0 mL intermediate
standard solution into a 100 mL acid-washed volumetric flask.
Add 10 mL analytical grade HNO3, dilute to volume with
H2O, mix, and transfer to acid-washed polypropylene bottle.
(4) Std3.—Pipet 2.0 mL intermediate standard solution into a
100 mL acid-washed volumetric flask. Add 10 mL analytical
grade HNO3, dilute to volume with H2O, mix, and transfer to
acid-washed polypropylene bottle. (5) Std2.—Pipet 1.0 mL
intermediate standard solution into a 100 mL acid-washed
volumetric flask. Add 10 mL analytical grade HNO3, dilute to
POITEVIN ET AL.: JOURNAL OF AOAC I NTERNATIONAL VOL. 92, NO. 5, 2009 1493
Table 10. Median recovery (%) and standard deviations
(%) by element and for all elements in eight food-grade
salts using recommended lines
Recovery, %b
Spiked element Concn, mg/La Without Csc With Cs 1% w/vd
Calcium 60 93 ± 4 101 ± 4
Copper 0.4 92 ± 3 105 ± 4
Iron 2 92 ± 3 101 ± 4
Potassium 80 117 ± 18 105 ± 5
Magnesium 20 95 ± 5 102 ± 6
Manganese 0.01 95 ± 7 105 ± 6
Sodium 40 110 ± 14 103 ± 5
Phosphorus 40 90 ± 7 102 ± 4
Zinc 0.8 91 ± 7 103 ± 6
All elementse
0.01–60 94 ± 9 103 ± 5
a Concentration of spiked element in salt solution.b Average of spiked element recoveries in all food-grade salts
solutions.c Recovery value without Cs ion buffer addition.d Recovery value with Cs ion buffer 1% (w/v) addition.e Median of all spiked elements recoveries in all food-grade salts.
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volume with H2O, mix and transfer to acid-washed
polypropylene bottle. (6 ) Std1.—Pipet 0.5 mL intermediate
standard solution into a 100 mL acid-washed volumetric flask.
Add 10 mL analytical grade HNO3, dilute to volume with
H2O, mix, and transfer to acid-washed polypropylene bottle.
All calibration solutions should be stable for 1 week.
(g) Test portion preparation.—Three single test portions
were first extracted using a small weighing spatula from each
of the five amber PVC 100 mL boxes (Greiner Bio-one)containing 10 g of test sample (Table 2), then weighed, and
finally prepared as described for SLV before MCD or MDO
microwave digestions.
(h) Sample digestion.—All 15 test portions (i.e.,
triplicates extracted from each of the five test samples) were
digested according to MCD or MDO programs adapted or
similar to those described for SLV (Mars Xpress and MDS
2000 systems, respectively). Information was provided to
collaborators concerning the maximum concentration for each
element in the five delivered food matrixes in order to
pre-adapt the final dilution of digest test portions before
ICP-AES analysis.
(i) Detection.—Digested test solutions, or appropriate
dilutions were presented to the ICP-AES instrument
calibrated as described for SLV with acid-matched standard
calibrant solutions.
( j) Calculations.—Element concentrations in the five
food matrixes were calculated using the equation described
for SLV in the ICP Analysis Section, part (c).
(k ) Statistical calculations.—Medians, SDr , and SDiR ,
repeatability (r) and reproducibility (R) limits, z -scores, and
HorRat values for nine elements in five blind samples
prepared in triplicate were determined by a statistical
treatment of 45 data sets.
(l) Repeatability and reproducibility limits.— Repeatability limit r, which is the maximum tolerated relative
variation between two measurements taken by a single person
or instrument on the same matrix and under the same
conditions, is expressed as follows:
2.772 SDr
where SDr is the repeatability standard deviation.
Reproducibility limit R is the maximum variation between
two measurements taken by several persons in different
laboratories, on different days, under different conditions, and
is expressed as follows:
2.772 SDR
where SDR is the reproducibility standard deviation.
(m) Z-score.—Evaluation of the whole laboratory
performance in term of accuracy was obtained based on the
calculation of the z -score. The z-score “ z ” is given by the
following equation:
z x X
RSDR
where x is the found mean value of analyte concentration in
the test material calculated from the nine means reported by
the nine laboratories; X is the certified (or reference) value of
the certified (or in-house) reference material; RSDR is the
relative reproducibility standard deviation.
If z 2, the result is satisfactory; if 2 < z < 3, the result is
questionable; if z > 3, the result is unsatisfactory.
(n) HorRat values.—HorRat values for each element in
each of the five matrixes were calculated as follows:
HorRat value = RSD , %
2C , %
R
0.1505
where RSDR is the relative reproducibility standard deviation
of each element in each of the five tested matrixes; C is the
relative concentration (expressed as dimensionless mass
fraction) of the analyte in question (valid for concentration
ratio above 10 –9).
The original data developed from interlaboratory studies
were assigned a HorRat value of 1.0 with limits of
acceptability of 0.5–2.0. Consistent deviations from the ratio
on the low side (values <0.5) may indicate unreportedaveraging or excellent training and experience; consistent
deviations on the high side (values >2) may indicate
inhomogeneity of the test samples, need for further method
optimization or training, operating below the LOD, or an
unsatisfactory method.
(o) Horwitz equation.—Horwitz equation expressed using
log scale (log SDR = 0.8495 log C 1.6991) was compared with
a similar equation found using the 45 SDR values and medians
of concentration (i.e., SDR and median values for nine
elements in five matrixes) obtained from the data treatment of
the RT.
Results and Discussion
SLV
(a) Closed-vessel microwave digestion optimization.—
Average values of each element concentration in whole egg
powder, baby food composite, and baking chocolate fell
within confidence intervals of reference value for the three
matrixes and are in agreement with AOAC recovery criteria,
except for iron and copper in baking chocolate, with recovery
values of 123 and 125%, respectively, and for phosphorus in
whole egg powder, with a recovery value of 116% (Table 6).
Significant variation of results for iron and copper in baking
chocolate have previously been observed (34). The higher
value of recovery for phosphorus in whole egg powder is due
to the use of the optimized microwave program in CEM Mars
Xpress, whereas generally lower values are obtained with a
program leading to incomplete digestion (6, 8). This single
optimized microwave digestion program on a CEM Mars
Xpress system is adapted to be applicable to various matrixes
covering the AOAC food triangle.
(b) Linearity.—The calibration curves constructed by
plotting element concentration versus peak ratio response
(element/IS) showed good linearity either in linear or in
weighted nonlinear regression (Table 7). Weighted nonlinear
1494 POITEVIN ET AL.: JOURNAL OF AOAC I NTERNATIONAL VOL. 92, NO. 5, 2009
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POITEVIN ET AL.: JOURNAL OF AOAC I NTERNATIONAL VOL. 92, NO. 5, 2009 1495
T a b l e
1 1 .
S L V s t u d y : a c c u r a c
y , p r e c i s i o n , a n d H o r R a t v a l u e s f o u n
d f o r c a l c i u m
i n s e v e n c e r t i f i e d a n d i n - h o u s e r e f e r e n c e m a t e r i a l s u s i n g r e c o m m e n d e d a n d
a l t e r n a t e l i n e s
M a t e r i a l d e s c r i p t i o n
L i n e
R e f e r e n c e
v a l u e , m g / k g a , b
M e d i a n ± U ,
m g / k g c
R e c o v e r y , %
P - v a l u e
d
S D r , m g / k g e
S D i R , m g / k g
f
R S D r ,
%
R
S D i R , %
H o r R a t g
S t e r i l i z e d c r e a m
C a
h
8 4 5 ± 1 8
7 5 6 ± 1 3 2
9 0 ± 5
0 . 0 7
7 2
1 2 5
9 . 5
1 6 . 5
2 . 8
C a
i
7 2 6 ± 1 3 2
8 6 ± 5
0 . 0 2
6 7
1 1 2
9 . 3
1 5 . 4
2 . 6
C h o c o l a t e m i l k p o w d e r
C a
h
9 8 7 0 ± 1 2 4
1 0 0 9 2 ± 3 4 3
1 0 2 ± 2
0 . 2 1
1 3 5
3 0 3
1 . 3
3 . 0
0 . 7
C a
i
9 8 8 2 ± 1 7 9
1 0 0 ± 1
0 . 9 3
1 1 7
1 3 3
1 . 2
1 . 3
0 . 3
I n f a n t c e r e a l s
C a
h
6 0 0 0 ± 4 4
6 1 8 9 ± 2 4 9
1 0 3 ± 1
0 . 0 5
1 5 1
2 1 9
2 . 4
3 . 5
0 . 8
C a
i
5 9 8 3 ± 2 1 5
1 0 0 ± 1
0 . 8 2
1 6 0
2 0 4
2 . 7
3 . 4
0 . 8
C o r n b r a n
C a
h
4 2 0 ± 1 9
4 3 5 ± 2 9
1 0 4 ± 5
0 . 6 0
6
2 0 . 0
1 . 4
4 . 5
0 . 7
C a
i
4 2 4 ± 2 4
1 0 1 ± 5
0 . 9 7
6
1 4
1 . 4
3 . 3
0 . 5
D i e t e t i c m i l k p o w d e r 1
C a
h
3 0 2 0 ± 1 5
3 0 4 7 ± 5 6
1 0 1 ± 1
0 . 3 5
3 3
4 9
1 . 1
1 . 6
0 . 3
C a
i
2 9 8 7 ± 5 4
9 9 ± 1
0 . 1 1
2 2
4 9
0 . 7
1 . 7
0 . 4
P e t f o o d
C a
h
6 1 9 0 ± 1 4 0
6 5 8 0 ± 3 1 7
1 0 6 ± 3
0 . 0 5
9 4
1 9 2
1 . 4
2 . 9
0 . 7
C a
i
6 4 1 0 ± 2 1 2
1 0 4 ± 3
0 . 1 8
9 2
1 5 0
1 . 4
2 . 3
0 . 5
N o n f a t m i l k p o w d e r
C a
h
1 3 0 0 0 ± 2 5 0
1 3 0 7 0 ± 9 8 8
1 0 1 ± 3
0 . 8 6
2 0 6
9 0 8
1 . 6
6 . 9
1 . 8
C a
i
1 2 9 1 0 ± 8 1 3
9 9 ± 3
0 . 8 0
2 2 2
7 3 5
1 . 7
5 . 7
1 . 5
a
S D e x p r e s s e d a s h a l f o f s t a t e d u n c
e r t a i n t y ( N I S T a n d L G C c e r t i f i e d m a t e r i a l s ) g
i v e n a s 9 5 % c o n f i d e n c e i n t e r v a l .
b
S D e x p r e s s e d a s a r e p r o d u c i b i l i t y S
D ( i n - h o u s e r e f e r e n c e m a t e r i a l s ) c a l c u l a t e d
a c c o r d i n g t o r o b u s t s t a t i s t i c s ( 2 9 ) .
c
U n c e r t a i n t y ( U ) e s t i m a t e d t h r o u g h s i m p l i f i e d a p p r o a c h ( 3 0 , 3 1 ) .
d
S t a t i s t i c e v a l u a t i o n o f r o b u s t t - t e s t :
S a t i s f a c t o r y r e s u l t ( P
> 0 . 0 5 ) ; q u e s t i o n a b l e r
e s u l t ( 0 . 0 1 < P
< 0 . 0 5 ) ; u n s a t i s f a c t o r y r e s u l t ( P
< 0 . 0 1 ) .
e
S D r = S D o f r e p e a t a b i l i t y .
f
S D i R = S D o f i n t e r m e d i a t e r e p r o d u c
i b i l i t y .
g
H o r R a t = R a t i o u s i n g R S D i R a n d H o r w i t z d e n o m i n a t o r a c c o r d i n g t o r e f . 3 2 .
h
R e c o m m e n d e d l i n e f o r I C P - A E S a n a l y s i s .
i
A l t e r n a t e c o n f i r m a t o r y l i n e s f o r I C P
- A E S a n a l y s i s .
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1496 POITEVIN ET AL.: JOURNAL OF AOAC I NTERNATIONAL VOL. 92, NO. 5, 2009
T a b l e
1 2 .
S L V s t u d y : a c c u r a c
y , p r e c i s i o n , a n d H o r R a t v a l u e s f o u n
d f o r c o p p e r i n t h r e e c e r t i f i e d a n d i n
- h o u s e r e f e r e n c e m a t e r i a l s u s i n g r e c
o m m e n d e d a n d
a l t e r n a t e l i n e s
M a t e r i a l d e s c r i p t i o n
L i n e
R e f e r e n c e
v a l u e , m g / k g a , b
M e d i a n ± U ,
m g / k g c
R
e c o v e r y , %
P - v a l u e
d
S D r , m g / k g e
S D i R , m g / k g
f
R S D r ,
%
R
S D i R , %
H o r R a t g
C o r n b r a n
C u
h
2 . 4 7 ± 0 . 2 0
2 . 6 9 ± 0 . 2 4
1 0 9 ± 9
0 . 3 6
0 . 0 5
0 . 0 9
1 . 8
3 . 1
0 . 2
C u i
2 . 6 1 ± 0 . 2 4
1 0 6 ± 9
0 . 5 3
0 . 0 5
0 . 1
1 . 9
3 . 9
0 . 3
C u i
2 . 5 6 ± 0 . 2 6
1 0 3 ± 9
0 . 7
0 . 0 6
0 . 1 5
2 . 4
5 . 6
0 . 4
C u i
2 . 5 2 ± 0 . 2 5
1 0 2 ± 8
0 . 8 2
0 . 0 6
0 . 1 4
2 . 5
5 . 4
0 . 4
D i e t e t i c m i l k p o w d e r 1
C u
h
7 . 5 5 ± 0 . 1 3
7 . 7 8 ± 0 . 2 1
1 0 3 ± 2
0 . 1 5
0 . 0 9
0 . 1 5
1 . 1
2
0 . 2
C u i
7 . 6 3 ± 0 . 2 3
1 0 1 ± 2
0 . 6
0 . 0 8
0 . 1 8
1
2 . 4
0 . 2
C u i
7 . 7 2 ± 0 . 2 5
1 0 2 ± 2
0 . 2 8
0 . 0 8
0 . 2
1
2 . 6
0 . 2
C u i
7 . 5 8 ± 0 . 2 1
1 0 0 ± 2
0 . 8 4
0 . 0 8
0 . 1 5
1
2
0 . 2
N o n f a t m i l k p o w d e r
C u
h
0 . 7 0 ± 0 . 0 5
0 . 7 5 ± 0 . 0 8
1 0 7 ± 8
0 . 4 4
0 . 0 6
0 . 0 6
8 . 3
8 . 5
0 . 5
C u i
0 . 7 8 ± 0 . 1 1
1 1 2 ± 9
0 . 2 2
0 . 0 6
0 . 0 9
8 . 3
1 1 . 4
0 . 7
C u i
0 . 7 8 ± 0 . 0 9
1 1 2 ± 8
0 . 2 1
0 . 0 5
0 . 0 7
7
8 . 5
0 . 5
C u i
0 . 7 9 ± 0 . 1 0
1 1 3 ± 9
0 . 1 7
0 . 0 5
0 . 0 8
6 . 8
1 0 . 2
0 . 6
a
S D e x p r e s s e d a s h a l f o f s t a t e d u n c
e r t a i n t y ( N I S T a n d L G C c e r t i f i e d m a t e r i a l s ) g
i v e n a s 9 5 % c o n f i d e n c e i n t e r v a l .
b
S D e x p r e s s e d a s a r e p r o d u c i b i l i t y S
D ( i n - h o u s e r e f e r e n c e m a t e r i a l s ) c a l c u l a t e d
a c c o r d i n g t o r o b u s t s t a t i s t i c s ( 2 9 ) .
c
U n c e r t a i n t y ( U ) e s t i m a t e d t h r o u g h s i m p l i f i e d a p p r o a c h ( 3 0 , 3 1 ) .
d
S t a t i s t i c e v a l u a t i o n o f r o b u s t t - t e s t :
S a t i s f a c t o r y r e s u l t ( P
> 0 . 0 5 ) ; q u e s t i o n a b l e r
e s u l t ( 0 . 0 1 < P
< 0 . 0 5 ) ; u n s a t i s f a c t o r y r e s u l t
( P
< 0 . 0 1 ) .
e
S D r = S D o f r e p e a t a b i l i t y .
f
S D i R = S D o f i n t e r m e d i a t e r e p r o d u c
i b i l i t y .
g
H o r R a t = R a t i o u s i n g R S D i R a n d H o r w i t z d e n o m i n a t o r a c c o r d i n g t o r e f . 3 2 .
h
R e c o m m e n d e d l i n e f o r I C P - A E S a n a l y s i s .
i
A l t e r n a t e c o n f i r m a t o r y l i n e s f o r I C P
- A E S a n a l y s i s .
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POITEVIN ET AL.: JOURNAL OF AOAC I NTERNATIONAL VOL. 92, NO. 5, 2009 1497
T a b l e
1 3 .
S L V s t u d y : a c c u r a c
y , p r e c i s i o n , a n d H o r R a t v a l u e s f o u n
d f o r i r o n i n f o u r c e r t i f i e d a n d i n - h o u
s e r e f e r e n c e m a t e r i a l s u s i n g r e c o m m e n d e d a n d a l t e r n a t e
l i n e s
M a t e r i a l d e s c r i p t i o n
L i n
e
R e f e r e n c e
v a l u e , m g / k g a , b
M e d i a n ± U ,
m g / k g c
R e c o v e r y , %
P - v a l u e
d
S D r , m g / k g e
S D i R , m g / k g
f
R S D r ,
%
R
S D i R , %
H o r R a t g
C h o c o l a t e m i l k p o w d e r
F e
h
1 6 9 . 9 ± 2 . 4
1 6 6 . 9 ± 1 2 . 0
9 8 ± 2
0 . 3 3
1 3 . 2
1 1 . 7
7 . 9
7 . 0
1 . 0
F e
i
1 6 3 . 1 ± 1 2 . 4
9 6 ± 2
0 . 1 0
1 3 . 1
1 2 . 2
7 . 9
7 . 3
0 . 8
F e
i
1 6 6 . 6 ± 1 3 . 1
9 8 ± 2
0 . 3 5
1 3 . 3
1 2 . 7
8 . 0
7 . 6
1 . 2
I n f a n t c e r e a l s
F e
h
8 0 . 4 ± 0 . 6
7 9 . 6 ± 1 . 3
9 9 ± 1
0 . 2 8
1 . 0
1 . 1
1 . 2
1 . 4
1 . 0
F e
i
7 9 . 0 ± 1 . 2
9 8 ± 1
0 . 0 9
1 . 0
1 . 1
1 . 3
1 . 3
0 . 7
F e
i
7 9 . 5 ± 1 . 3
9 9 ± 1
0 . 2 5
1 . 1
1 . 2
1 . 3
1 . 4
0 . 3
C o r n b r a n
F e
h
1 4 . 8 ± 0 . 9
1 4 . 7 ± 1 . 3
9 9 ± 6
0 . 8 8
0 . 2
1 . 0
1 . 3
6 . 7
0 . 2
F e
i
1 4 . 7 ± 1 . 2
9 9 ± 6
0 . 9 2
0 . 2
0 . 8
1 . 3
5 . 4
0 . 3
F e
i
1 4 . 7 ± 1 . 1
9 9 ± 6
0 . 8 8
0 . 2
0 . 7
1 . 4
4 . 8
0 . 3
D i e t e t i c m i l k p o w d e r 1
F e
h
5 8 . 5 ± 0 . 4
5 9 . 3 ± 0 . 9
1 0 1 ± 1
0 . 1 1
0 . 8
0 . 8
1 . 3
1 . 3
0 . 2
F e
i
5 9 . 1 ± 0 . 9
1 0 1 ± 1
0 . 2 4
0 . 7
0 . 8
1 . 1
1 . 4
0 . 3
F e
i
5 9 . 1 ± 1 . 0
1 0 1 ± 1
0 . 2 6
0 . 7
0 . 9
1 . 1
1 . 5
0 . 4
a
S D e x p r e s s e d a s h a l f o f s t a t e d u n c
e r t a i n t y ( N I S T a n d L G C c e r t i f i e d m a t e r i a l s ) g
i v e n a s 9 5 % c o n f i d e n c e i n t e r v a l .
b
S D e x p r e s s e d a s a r e p r o d u c i b i l i t y S
D ( i n - h o u s e r e f e r e n c e m a t e r i a l s ) c a l c u l a t e d
a c c o r d i n g t o r o b u s t s t a t i s t i c s ( 2 9 ) .
c
U n c e r t a i n t y ( U ) e s t i m a t e d t h r o u g h s i m p l i f i e d a p p r o a c h ( 3 0 , 3 1 ) .
d
S t a t i s t i c e v a l u a t i o n o f r o b u s t t - t e s t :
S a t i s f a c t o r y r e s u l t ( P
> 0 . 0 5 ) ; q u e s t i o n a b l e r
e s u l t ( 0 . 0 1 < P
< 0 . 0 5 ) ; u n s a t i s f a c t o r y r e s u l t
( P
< 0 . 0 1 ) .
e
S D r = S D o f r e p e a t a b i l i t y .
f
S D i R = S D o f i n t e r m e d i a t e r e p r o d u c
i b i l i t y .
g
H o r R a t = R a t i o u s i n g R S D i R a n d H o r w i t z d e n o m i n a t o r a c c o r d i n g t o r e f . 3 2 .
h
R e c o m m e n d e d l i n e f o r I C P - A E S a n a l y s i s .
i
A l t e r n a t e c o n f i r m a t o r y l i n e s f o r I C P
- A E S a n a l y s i s .
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regression was used during SLV, MD1, and MD2 tests, as the
best regression coefficients are obtained with R 2 > 0.99995 for
all lines except for 1K766.491 (R 2 = 0.99924) and for 2Ca317.933 (R 2 = 0.99994) lines.
(c) LOD and LOQ.—The detection and quantification
limits of elements in real matrixes were estimated in Table 8
by affecting a dilution factor of 100 (i.e., corresponding to
0.5 g digest sample diluted to 50 mL solution after MDC and
before ICP-AES analysis) to the DL and QL, as satisfactory
trueness/RSDr and RSDiR values were found for elements
present in real matrixes at these concentrations (e.g., Ca, Cu,
Fe, K, Na, P in corn bran; Mg, Zn in sterilized cream, and Mn
in nonfat milk powder).
(d) Selectivity.—Element mean recoveries and associated
SD values calculated from spiked element of interest in eight
different solutions of food-grade salts are displayed in
Table 9. Good recoveries ranging between 88 and 115% were
found in all food-grade salt solutions with SDs ranging
between 0.1 and 18.8% for spiking that ranged between 0.01
and 60 mg/L, respectively. Comparative t -tests have shown
that recovery and SD values obtained from all averages of element spiked duplicates in all food-grade salt solutions with
and withoutadded ion buffer Cs 1% (w/v) are different at 95%
confidence with better recoveries and SD values (103 ± 5%)
using ion buffer Cs 1% (w/v; Table 10).
(e) Accuracy.—Statistic treatment of accuracy values
(trueness/recovery) displayed in Tables 11–19 for seven
matrixes tested has shown global satisfactory results (i.e.,
P -value >0.05: recovery not significantly different from
100%, at 95% level of confidence interval). Questionable
recoveries (i.e., 0.01 < P -value <0.05: recovery statistically
different from 100% at 95% level of confidence interval, but
not significantly different from 100% at 99% confidence
interval) were found for Ca and K in sterilized cream (86 ± 5%
and 120 ± 7%, respectively) using 2CaII and 1KI lines, for Mg
and Zn in dietetic milk powder 1 (98 ± 1% and 97 ± 1%,
respectively) using 3Mg, 1ZnI, and 3ZnI lines and for P in
infant cereals (104 ± 1%) using 1P line. AOAC requirements
for recovery are, however, globally fulfilled for all elements in
all matrixes (recovery range 79–120%) for concentrations
between 0.26 mg/kg (Mn) and 16 900 mg/kg (K). Only
recovery values for 2CaII and 1KI lines in sterilized cream
showed unacceptable values by AOAC criteria, as previously
demonstrated width statistic recovery test at 95% confidence.
(f ) Precision.—SDr and SDiR values, respectively,
displayed in Tables 13–21 for seven matrixes tested fulfillAOAC criteria regarding RSDr and RSDiR values for all
elements in all matrixes ranging between 0.6 and 16.8% and
between 0.9 and 23.3%, respectively, for concentrations
between 0.26 mg/kg (Mn) and 16 900 mg/kg (K).
(g) Uncertainty.—Overall uncertainty measurements
(±U) are displayed in Tables 11–19 with medians obtained
through reproducibility conditions as combinations of
precision (SDiR ) and trueness (SDrec) contributions.
Calculated derived relative U values range from 1 to 26% for
all elements in the seven tested matrixes.
1498 POITEVIN ET AL.: JOURNAL OF AOAC I NTERNATIONAL VOL. 92, NO. 5, 2009
T a b l e
1 4 .
S L V s t u d y : a c c u r a c
y , p r e c i s i o n , a n d H o r R a t v a l u e s f o u n
d f o r p o t a s s i u m
i n s i x c e r t i f i e d a n d i n - h o u s e r e f e r e n c e m a t e r i a l s u s i n g r e
c o m m e n d e d a n d
a l t e r n a t e l i n e s
M a t e r i a l d e s c r i p t i o n
L i n e
R e f e r e n c e
v a l u e , m g / k g a , b
M e d i a n ± U ,
m g / k g c
R e
c o v e r y , %
P - v a l u e
d
S D r , m g / k g e
S D i R , m g / k g
f
R S D r ,
%
R
S D i R , %
H o r R a t g
S t e r i l i z e d c r e a m
K h
1 1 6 0 ± 5 0
1 3 9 5 ± 2 0 3
1 2 0 ± 7
0 . 0 2
5 4
1 4 6
3 . 9
1 0 . 5
2 . 0
C h o c o l a t e m i l k p o w d e r
K h
9 0 9 0 ± 1 3 3
8 7 2 6 ± 4 6 8
9 6 ± 2
0 . 0 3
1 2 5
3 9 9
1 . 4
4 . 6
1 . 1
I n f a n t c e r e a l s
K h
6 5 0 0 ± 5 0
6 4 2 3 ± 4 8 5
9 9 ± 3
0 . 6 6
1 0 8
4 5 4
1 . 7
7 . 1
1 . 7
C o r n b r a n
K h
5 6 6 ± 3 8
5 3 1 ± 6 0
9 4 ± 7
0 . 7 0
1 0
4 6
1 . 8
8 . 6
1 . 4
D i e t e t i c m i l k p o w d e r 1
K h
5 5 7 0 ± 2 5
5 6 0 0 ± 1 7 5
1 0 1 ± 1
0 . 8 8
5 4
1 5 4
1 . 0
2 . 8
0 . 6
N o n f a t m i l k p o w d e r
K h
1 6 9 0 0 ± 1 5 0
1 7 0 0 8 ± 1 3 4 2
1 0 1 ± 2
0 . 7 7
3 2 2
9 5 8
1 . 9
5 . 6
1 . 5
a
S D e x p r e s s e d a s h a l f o f s t a t e d u n c
e r t a i n t y ( N I S T a n d L G C c e r t i f i e d m a t e r i a l s ) g
i v e n a s 9 5 % c o n f i d e n c e i n t e r v a l .
b
S D e x p r e s s e d a s a r e p r o d u c i b i l i t y S
D ( i n - h o u s e r e f e r e n c e m a t e r i a l s ) c a l c u l a t e d
a c c o r d i n g t o r o b u s t s t a t i s t i c s ( 2 9 ) .
c
U n c e r t a i n t y ( U ) e s t i m a t e d t h r o u g h s i m p l i f i e d a p p r o a c h ( 3 0 , 3 1 ) .
d
S t a t i s t i c e v a l u a t i o n o f r o b u s t t - t e s t :
S a t i s f a c t o r y r e s u l t ( P
> 0 . 0 5 ) ; q u e s t i o n a b l e r
e s u l t ( 0 . 0 1 < P
< 0 . 0 5 ) ; u n s a t i s f a c t o r y r e s u l t ( P
< 0 . 0 1 ) .
e
S D r = S D o f r e p e a t a b i l i t y .
f
S D i R = S D o f i n t e r m e d i a t e r e p r o d u c
i b i l i t y .
g
H o r R a t = R a t i o u s i n g R S D i R a n d H o r w i t z d e n o m i n a t o r a c c o r d i n g t o r e f . 3 2 .
h
R e c o m m e n d e d l i n e f o r I C P - A E S a n a l y s i s .
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T a b l e
1 5 .
S L V s t u d y : a c c u r a c
y , p r e c i s i o n , a n d H o r R a t v a l u e s f o u n
d f o r m a g n e s i u m
i n s e v e n c e r t i f i e d a
n d i n - h o u s e r e f e r e n c e m a t e r i a l s u s i n g r e c o m m e n d e d a n d
a l t e r n a t e l i n e s
M a t e r i a l d e s c r i p t i o n
L i n e
R e f e r e n c e
v a l u e , m g / k g a ,
b
M e d i a n ± U ,
m g / k g c
R e
c o v e r y , %
P - v a l u e
d
S D r , m g / k g e
S D i R , m g / k g
f
R S D r ,
%
R
S D i R , %
H o r R a t g
S t e r i l i z e d c r e a m
M g
h
8 4 . 4 ± 2 . 0
8 1 . 7 ± 4 . 5
9 7 ± 3
0 . 2 8
2 . 0
3 . 9
2 . 4
4 . 7
0 . 6
M g
i
7 9 . 9 ± 4 . 2
9 5 ± 3
0 . 0 8
1 . 7
3 . 6
2 . 1
4 . 5
0 . 5
M g
i
8 2 . 7 ± 4 . 4
9 8 ± 3
0 . 4 8
2 . 3
3 . 8
2 . 7
4 . 6
0 . 6
C h o c o l a t e m i l k p o w d e r
M g
h
1 7 7 9 ± 2 3
1 7 7 1 ± 2 2
1 0 0 ± 1
0 . 8 2
2 3
3 2
1 . 3
1 . 8
0 . 3
M g
i
1 7 5 7 ± 6 7
9 9 ± 2
0 . 4 8
2 2
5 9
1 . 3
3 . 4
0 . 7
M g
i
1 7 4 4 ± 5 4
9 8 ± 2
0 . 2 2
2 1
4 7
1 . 2
2 . 7
0 . 5
I n f a n t c e r e a l s
M g
h
8 8 1 ± 8
9 1 1 ± 4 6
1 0 3 ± 2
0 . 1 0
2 5
4 3
2 . 7
4 . 7
0 . 8
M g
i
9 0 2 ± 4 3
1 0 2 ± 2
0 . 2 2
2 1
4 0
2 . 3
4 . 5
0 . 8
M g
i
8 9 2 ± 4 8
1 0 1 ± 2
0 . 5 3
2 4
4 6
2 . 7
5 . 1
0 . 9
C o r n b r a n
M g
h
8 1 8 ± 3 0
7 9 1 ± 4 5
9 7 ± 4
0 . 5 3
9
3 5
1 . 1
4 . 4
0 . 8
M g
i
7 7 5 ± 4 5
9 5 ± 4
0 . 2 5
8
3 3
1 . 0
4 . 2
0 . 7
M g
i
7 8 5 ± 4 0
9 6 ± 4
0 . 4 1
9
2 6
1 . 1
3 . 3
0 . 6
D i e t e t i c m i l k p o w d e r 1
M g
h
1 2 0 0 ± 8
1 2 0 6 ± 2 5
1 0 1 ± 1
0 . 8 8
8 . 0
2 3
0 . 7
1 . 9
0 . 3
M g
i
1 1 8 0 ± 3 0
9 8 ± 1
0 . 0 6
7 . 0
2 8
0 . 6
2 . 3
0 . 4
M g
i
1 1 8 1 ± 3 4
9 8 ± 1
0 . 0 3
9
2 9
0 . 8
2 . 5
0 . 5
P e t f o o d
M g
h
4 8 1 ± 2
4 8 3 ± 8
1 0 1 ± 1
0 . 3 1
7
8
1 . 4
1 . 6
0 . 3
M g
i
4 7 1 ± 1 2
9 8 ± 1
0 . 0 8
6
1 1
1 . 2
2 . 4
0 . 4
M g
i
4 7 7 ± 1 2
9 9 ± 1
0 . 5 2
8
1 1
1 . 6
2 . 3
0 . 4
N o n f a t m i l k p o w d e r
M g
h
1 2 0 0 ± 1 5
1 2 0 6 ± 8 9
1 0 1 ± 3
0 . 8 7
1 8
8 3
1 . 5
6 . 9
1 . 3
M g
i
1 1 8 6 ± 7 0
9 9 ± 2
0 . 6 0
1 9
6 5
1 . 6
5 . 5
1 . 0
M g
i
1 1 5 6 ± 8 7
9 6 ± 3
0 . 2 1
1 6
8 1
1 . 4
7 . 0
1 . 3
a
S D e x p r e s s e d a s h a l f o f s t a t e d u n c
e r t a i n t y ( N I S T a n d L G C c e r t i f i e d m a t e r i a l s ) g
i v e n a s 9 5 % c o n f i d e n c e i n t e r v a l .
b
S D e x p r e s s e d a s a r e p r o d u c i b i l i t y S
D ( i n - h o u s e r e f e r e n c e m a t e r i a l s ) c a l c u l a t e d
a c c o r d i n g t o r o b u s t s t a t i s t i c s ( 2 9 ) .
c
U n c e r t a i n t y ( U ) e s t i m a t e d t h r o u g h s i m p l i f i e d a p p r o a c h ( 3 0 , 3 1 ) .
d
S t a t i s t i c e v a l u a t i o n o f r o b u s t t - t e s t :
S a t i s f a c t o r y r e s u l t ( P
> 0 . 0 5 ) ; q u e s t i o n a b l e r
e s u l t ( 0 . 0 1 < P
< 0 . 0 5 ) ; u n s a t i s f a c t o r y r e s u l t
( P
< 0 . 0 1 ) .
e
S D r = S D o f r e p e a t a b i l i t y .
f
S D i R = S D o f i n t e r m e d i a t e r e p r o d u c
i b i l i t y .
g
H o r R a t = R a t i o u s i n g R S D i R a n d H o r w i t z d e n o m i n a t o r a c c o r d i n g t o r e f . 3 2 .
h
R e c o m m e n d e d l i n e f o r I C P - A E S a n a l y s i s .
i
A l t e r n a t e c o n f i r m a t o r y l i n e s f o r I C P
- A E S a n a l y s i s .
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1500 POITEVIN ET AL.: JOURNAL OF AOAC I NTERNATIONAL VOL. 92, NO. 5, 2009
T a b l e
1 6 .
S L V s t u d y : a c c u r a c
y , p r e c i s i o n , a n d H o r R a t v a l u e s f o u n
d f o r m a n g a n e s e i n t h r e e c e r t i f i e d a n d i n - h o u s e r e f e r e n c e m a t e r i a l s u s i n
g r e c o m m e n d e d a n d
a l t e r n a t e l i n e s
M a t e r i a l d e s c r i p t i o n
L i n e
R e f e r e n c e
v a l u e , m g / k g a , b
M e d i a n ± U ,
m g / k g c
R e c o v e r y , %
P - v a l u e
d
S D r , m g / k g e
S D i R , m g / k g
f
R S D r ,
%
R S D i R , %
H o r R a t g
C o r n b r a n
M n
h
2 . 5 5 ± 0 . 1 5
2 . 3 3 ± 0 . 1 8
9 1 ± 6
0 . 1 5
0 . 0 3
0 . 1 2
1 . 1
4 . 9
0 . 4
M n
i
2 . 5 5 ± 0 . 2 5
1
0 0 ± 6
0 . 9 6
0 . 0 3
0 . 2 0
1 . 1
7 . 3
0 . 5
M n
i
2 . 3 9 ± 0 . 1 7
9 4 ± 6
0 . 2 5
0 . 0 3
0 . 0 9
1 . 1
3 . 6
0 . 3
D i e t e t i c m i l k p o w d e r 1
M n
h
1 2 . 7 ± 0 . 8 5
1 2 . 8 ± 1 . 1
1
0 2 ± 7
0 . 8 3
0 . 2 7
0 . 6 8
2 . 1
5 . 3
0 . 5
M n
i
1 3 . 4 ± 1 . 3
1
0 5 ± 7
0 . 4 8
0 . 2 6
0 . 8 8
2 . 0
6 . 6
0 . 6
M n
i
1 2 . 8 ± 1 . 1
1
0 1 ± 7
0 . 8 8
0 . 2 4
0 . 6 7
1 . 8
5 . 2
0 . 5
N o n f a t m i l k p o w d e r
M n
h
0 . 2 6 ± 0 . 0 3
0 . 2 2 ± 0 . 0 3
8 5 ± 1 0
0 . 1 6
0 . 0 1
0 . 0 2
3 . 1
6 . 8
0 . 3
M n
i
0 . 2 0 ± 0 . 0 3
7 9 ± 9
0 . 0 6
0 . 0 1
0 . 0 2
3 . 8
1 0 . 8
0 . 5
M n
i
0 . 2 2 ± 0 . 0 3
8 5 ± 1 0
0 . 0 8
0 . 0 1
0 . 0 1
3 . 6
5 . 9
0 . 3
a
S D e x p r e s s e d a s h a l f o f s t a t e d u n c
e r t a i n t y ( N I S T a n d L G C c e r t i f i e d m a t e r i a l s ) g
i v e n a s 9 5 % c o n f i d e n c e i n t e r v a l .
b
S D e x p r e s s e d a s a r e p r o d u c i b i l i t y S
D ( i n - h o u s e r e f e r e n c e m a t e r i a l s ) c a l c u l a t e d
a c c o r d i n g t o r o b u s t s t a t i s t i c s ( 2 9 ) .
c
U n c e r t a i n t y ( U ) e s t i m a t e d t h r o u g h s i m p l i f i e d a p p r o a c h ( 3 0 , 3 1 ) .
d
S t a t i s t i c e v a l u a t i o n o f r o b u s t t - t e s t :
S a t i s f a c t o r y r e s u l t ( P
> 0 . 0 5 ) ; q u e s t i o n a b l e r
e s u l t ( 0 . 0 1 < P
< 0 . 0 5 ) ; u n s a t i s f a c t o r y r e s u l t
( P
< 0 . 0 1 ) .
e
S D r = S D o f r e p e a t a b i l i t y .
f
S D i R = S D o f i n t e r m e d i a t e r e p r o d u c
i b i l i t y .
g
H o r R a t = R a t i o u s i n g R S D i R a n d H o r w i t z d e n o m i n a t o r a c c o r d i n g t o r e f . 3 2 .
h
R e c o m m e n d e d l i n e f o r I C P - A E S a n a l y s i s .
i
A l t e r n a t e c o n f i r m a t o r y l i n e s f o r I C P
- A E S a n a l y s i s .
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(h) HorRat values.—HorRat values never exceed 1.5
except for several analytical lines of Ca (2.8 and 2.6), K (2.0),
Na (1.8), P (1.6), and Zn (1.6, 1.7) in sterilized cream, of Ca
(1.8), P (1.9, 2.2, 1.6) in nonfat milk powder, and of K in
infant cereals (1.7). However, the reliability and applicability
of the method is proved, as AOAC criteria are fulfilled with no
values higher than 3.0. If several values are between 0.2 and
0.5, this can be explained by experience, training of analysts, a
good knowledge of tested matrixes, and careful application.(i) Ruggedness.—Accuracy (SDrec) and intermediate
precision (SDiR ) results are displayed in Tables 20–28 for the
six matrixes tested. Global statistic recovery results were
satisfactory for all elements in all matrixes whatever the
digestion systems and ICP-AES equipments used.
Unsatisfactory statistic results ( P <0.01) were found mainly
for the infant cereals matrix: Ca for MD1 and MD3, Fe for
MD4, K for MD1, Mg for MD1 and MD3, and Na for MD4.
Other unsatisfactory results concern Ca in corn bran for MD4,
Cu in nonfat milk powder for MD3, Fe in dietetic milk
powder 1 and in corn bran for MD4, K in dietetic milk
powder 1 for MD1, P in corn bran for MD4, and Zn in dietetic
milk powder for MD1. Unsatisfactory statistical recovery
results mainly concern infant cereals matrix due to relative
heterogeneity of the used batch and corn bran matrix due to
whole element concentration values close to QL. These
statistical unsatisfactory results have shown that general
applicability of the method is limited by less analytical
experience and competency regarding sample preparation
(e.g., sample homogeneity and adapted digestion program)
and ICP analysis (adapted ion buffering and use of robust
conditions).
However, AOAC requirements for recovery performance
are globally fulfilled for all elements in all matrixes between
74 and 118% for element concentrations from 0.26 mg/kg(Mn) to 16 900 mg/kg (K). Only specific recovery values of
Ca (75%), Fe (72%), and P (68%) in corn bran for MD4; of K
(81 and 82%) for MD1 and MD2, respectively; recovery
values of Cu (67 and 74%) in nonfat milk powder and dietetic
milk powder for MD3 and MD4, respectively; and recovery
value of Ca (113%) in infant cereals for MD1 showed
unacceptable values regarding AOAC criteria, as already
demonstrated for statistic recovery test at 95% confidence.
AOAC requirements for RSDr and SDiR were fulfilled for
all elements in all matrixes between 0.6 and 18.9% and 0.9
and 23.3%, respectively, for concentrations from 0.26 mg/kg
(Mn) to 16 900 mg/kg (K).
These ruggedness tests have shown good robustness of thismethod applied by different operators (at least two operators
per test of eight analytical series) after open- and closed-vessel
digestions on different ICP-AES equipments with axial,
radial, and dual view grating configurations using Cs 0.1%
(w/v) as minimal ionization buffer concentration.
Ring Trial
(a) Calcium.—Table 29 presents estimated performance
characteristics of the ICP-AES method for determination of
Ca, Cu, Fe, K, Mg, Mn, Na, P, and Zn. The RSDr of the
POITEVIN ET AL.: JOURNAL OF AOAC I NTERNATIONAL VOL. 92, NO. 5, 2009 1501
T a b l e
1 7 .
S L V s t u d y : a c c u r a c
y , p r e c i s i o n , a n d H o r R a t v a l u e s f o u n
d f o r s o d i u m
i n s i x c e r t i f i e d a n d i n - h
o u s e r e f e r e n c e m a t e r i a l s u s i n g r e c o
m m e n d e d a n d a l t e r n a t e
l i n e s
M a t e r i a l d e s c r i p t i o n
L i n e
R e f e r e n c e
v a l u e , m g / k g a , b
M e d i a n ± U ,
m g / k g c
R e c o v e r y , %
P - v a l u e
d
S D r , m g / k g
e
S D i R , m g / k g
f
R S D r ,
%
R
S D i R , %
H o r R a t g
S t e r i l i z e d c r e a m
N A
h
5 0 5 ± 1 9
5 5 4 ± 6 7
1 1 0 ± 6
0 . 1 3
2
6
3 . 4
1 0 . 9
1 . 8
C h o c o l a t e m i l k p o w d e r
N A
h
1 9 9 0 ± 4 2
1 9 5 0 ± 7 4
9 8 ± 2
0 . 3 7
3 2
5 9
1 . 6
3 . 0
0 . 6
I n f a n t c e r e a l s
N A
h
1 0 5 0 ± 1 4
1 0 5 4 ± 6 4
1 0 0 ± 2
0 . 8 9
3 4
6 0
3 . 2
5 . 7
1 . 0
C o r n b r a n
N A
h
4 3 0 ± 1 6
4 2 4 ± 2 6
9 9 ± 4
0 . 4 0
6
1 9
1 . 5
4 . 4
0 . 7
D i e t e t i c m i l k p o w d e r 1
N A
h
4 9 2 0 ± 3 0
4 8 9 0 ± 8 7
9 9 ± 1
0 . 2 0
4 0
7 9
0 . 8
1 . 6
0 . 4
N o n f a t m i l k p o w d e r
N A
h
4 9 7 0 ± 5 0
4 9 1 0 ± 3 2 1
9 9 ± 1
0 . 6 1
6 5
2 9 7
1 . 3
6 . 1
1 . 4
a
S D e x p r e s s e d a s h a l f o f s t a t e d u n c
e r t a i n t y ( N I S T a n d L G C c e r t i f i e d m a t e r i a l s ) g
i v e n a s 9 5 % c o n f i d e n c e i n t e r v a l .
b
S D e x p r e s s e d a s a r e p r o d u c i b i l i t y S
D ( i n - h o u s e r e f e r e n c e m a t e r i a l s ) c a l c u l a t e d
a c c o r d i n g t o r o b u s t s t a t i s t i c s ( 2 9 ) .
c
U n c e r t a i n t y ( U ) e s t i m a t e d t h r o u g h s i m p l i f i e d a p p r o a c h ( 3 0 , 3 1 ) .
d
S t a t i s t i c e v a l u a t i o n o f r o b u s t t - t e s t :
S a t i s f a c t o r y r e s u l t ( P
> 0 . 0 5 ) ; q u e s t i o n a b l e r
e s u l t ( 0 . 0 1 < P
< 0 . 0 5 ) ; u n s a t i s f a c t o r y r e s u l t
( P
< 0 . 0 1 ) .
e
S D r = S D o f r e p e a t a b i l i t y .
f
S D i R = S D o f i n t e r m e d i a t e r e p r o d u c
i b i l i t y .
g
H o r R a t = R a t i o u s i n g R S D i R a n d H o r w i t z d e n o m i n a t o r a c c o r d i n g t o r e f . 3 2 .
h
R e c o m m e n d e d l i n e f o r I C P - A E S a n a l y s i s .
7/23/2019 Improvement of AOAC Official Method 984.27 for The
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1502 POITEVIN ET AL.: JOURNAL OF AOAC I NTERNATIONAL VOL. 92, NO. 5, 2009
T a b l e
1 8 .
S L V s t u d y : a c c u r a c
y , p r e c i s i o n , a n d H o r R a t v a l u e s f o u n
d f o r p h o s p h o r u s i n s e v e n c e r t i f i e d a n d i n - h o u s e r e f e r e n c e m a t e r i a l s u s i n g r e c o m m e n d e d a n d
a l t e r n a t e l i n e s
M a t e r i a l d e s c r i p t i o n
L i n e
R e f e r e n c e
v a l u e , m g / k g a , b
M e d i a n ± U ,
m g / k g c
R e
c o v e r y , %
P - v a l u e
d
S D r , m g / k g e
S D i R , m g / k g
f
R S D r ,
%
R
S D i R , %
H o r R a t g
S t e r i l i z e d c r e a m
P h
8 2 3 ± 2 2
8 0 7 ± 6 0
9 8 ± 3
0 . 5 6
3 2
5 3
4 . 0
6 . 6
1 . 1
P i
8 2 1 ± 5 6
9 9 ± 3
0 . 9 5
3 6
4 9
4 . 4
6 . 0
1 . 0
P i
7 8 3 ± 8 2
9 5 ± 4
0 . 2 6
3 2
7 6
4 . 1
9 . 6
1 . 6
C h o c o l a t e m i l k p o w d e r
P h
4 0 8 0 ± 3 0
4 1 1 0 ± 1 5 0
1 0 1 ± 1
0 . 6 0
6 7
1 3 8
1 . 6
3 . 4
0 . 7
P i
4 1 5 0 ± 8 8
1 0 2 ± 1
0 . 6 1
6 0
7 0
1 . 5
1 . 7
0 . 4
P i
4 0 5 0 ± 8 5
9 9 ± 1
0 . 5 9
6 0
7 0
1 . 6
1 . 8
0 . 4
I n f a n t c e r e a l s
P h
4 3 2 0 ± 2 1
4 4 7 0 ± 1 6 5
1 0 4 ± 1
0 . 0 2
5 3
1 3 6
1 . 2
3 . 1
0 . 7
P i
4 5 1 0 ± 2 9 7
1 0 4 ± 2
0 . 1 0
7 7
2 7 9
1 . 7
6 . 2
1 . 4
P i
4 3 4 0 ± 1 1 6
1 0 0 ± 1
0 . 6 9
6 3
1 1 0
1 . 5
2 . 5
0 . 6
C o r n b r a n
P h
1 7 1 ± 6
1 6 3 ± 1 8
9 5 ± 4
0 . 8 6
2
1 7
1 . 4
1 0 . 4
1 . 4
P i
1 6 6 ± 9
9 7 ± 4
0 . 4 4
2
7
1 . 3
4 . 4
0 . 6
P i
1 6 2 ± 8
9 5 ± 3
0 . 1 7
3
5
1 . 6
3 . 2
0 . 4
D i e t e t i c m i l k p o w d e r 1
P h
3 0 8 0 ± 1 1
3 1 0 0 ± 6 5
1 0 1 ± 1
0 . 2 7
2 8
5 8
0 . 9
1 . 9
0 . 4
P i
3 1 2 0 ± 6 8
1 0 1 ± 1
0 . 1 2
3 7
6 3
1 . 2
2 . 0
0 . 4
P i
3 0 8 0 ± 4 3
1 0 0 ± 1
0 . 6 5
2 1
3 9
0 . 7
1 . 3
0 . 3
P e t f o o d
P h
4 5 1 0 ± 4 0
4 6 3 0 ± 1 2 2
1 0 3 ± 1
0 . 0 5
4 8
9 2
1 . 0
2 . 0
0 . 4
P i
4 6 2 0 ± 1 7 6
1 0 2 ± 2
0 . 1 6
6 3
7 2
1 . 5
1 . 7
0 . 4
P i
4 4 9 0 ± 8 8
1 0 0 ± 1
0 . 6 7
6 1 . 0
7 8
1 . 3
1 . 7
0 . 4
N o n f a t m i l k p o w d e r
P h
1 0 6 0 0 ± 1 0 0
1 0 8 3 0 ± 8 4 5
1 0 2 ± 3
0 . 4 6
1 6 9
7 8 8
1 . 6
7 . 3
1 . 9
P i
1 0 8 4 0 ± 9 8 1
1 0 2 ± 3
0 . 5 0
2 0 0
9 2 2
1 . 8
8 . 5
2 . 2
P i
1 0 5 0 0 ± 7 0 7
9 9 ± 2
0 . 7 1
1 4 4
6 5 7
1 . 4
6 . 3
1 . 6
a
S D e x p r e s s e d a s h a l f o f s t a t e d u n c
e r t a i n t y ( N I S T a n d L G C c e r t i f i e d m a t e r i a l s ) g
i v e n a s 9 5 % c o n f i d e n c e i n t e r v a l .
b
S D e x p r e s s e d a s a r e p r o d u c i b i l i t y S
D ( i n - h o u s e r e f e r e n c e m a t e r i a l s ) c a l c u l a t e d
a c c o r d i n g t o r o b u s t s t a t i s t i c s ( 2 9 ) .
c
U n c e r t a i n t y ( U ) e s t i m a t e d t h r o u g h s i m p l i f i e d a p p r o a c h ( 3 0 , 3 1 ) .
d
S t a t i s t i c e v a l u a t i o n o f r o b u s t t - t e s t :
S a t i s f a c t o r y r e s u l t ( P
> 0 . 0 5 ) ; q u e s t i o n a b l e r
e s u l t ( 0 . 0 1 < P
< 0 . 0 5 ) ; u n s a t i s f a c t o r y r e s u l t ( P
< 0 . 0 1 ) .
e
S D r = S D o f r e p e a t a b i l i t y .
f
S D i R = S D o f i n t e r m e d i a t e r e p r o d u c
i b i l i t y .
g
H o r R a t = R a t i o u s i n g R S D i R a n d H o r w i t z d e n o m i n a t o r a c c o r d i n g t o r e f . 3 2 .
h
R e c o m m e n d e d l i n e f o r I C P - A E S a n a l y s i s .
i
A l t e r n a t e c o n f i r m a t o r y l i n e s f o r I C P
- A E S a n a l y s i s .
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T a b l e
1 9 .
S L V s t u d y : a c c u r a c
y , p r e c i s i o n , a n d H o r R a t v a l u e s f o u n
d f o r z i n c i n f o u r c e r t i f i e d a n d i n - h o u
s e r e f e r e n c e m a t e r i a l s u s i n g r e c o m m e n d e d a n d a l t e r n a t e
l i n e s
M a t e r i a l d e s c r i p t i o n
L i n e
R e f e r e n c e
v a l u e , m g / k g a , b
M e d i a n ± U ,
m g / k g c
R e c o v e r y , %
P - v a l u e
d
S D r , m g / k g e
S D i R , m g / k g
f
R S D r ,
%
R S D i R , %
H o r R a t g
S t e r i l i z e d c r e a m
Z n
h
3 . 1 ± 0 . 2
2 . 6 ± 0 . 6
8 3 ± 7
0 . 0 5
0 . 4
0 . 6 0
1 6 . 9
2 2 . 5
1 . 6
Z n
i
2 . 7 ± 0 . 6
8 8 ± 7
0 . 1 4
0 . 5
0 . 5 0
1 6 . 7
1 9 . 3
1 . 4
Z n
i
2 . 6 ± 0 . 7
8 2 ± 8
0 . 0 5
0 . 4
0 . 6 0
1 6 . 8
2 3 . 3
1 . 7
C o r n b r a n
Z n
h
1 8 . 6 ± 1 . 1
1 7 . 6 ± 1 . 3
9 5 ± 6
0 . 3 8
0 . 8
2 . 1
1 . 8
4 . 5
0 . 4
Z n
i
1 7 . 8 ± 1 . 4
9 6 ± 6
0 . 5 0
0 . 2
0 . 9
1 . 2
5 . 0
0 . 4
Z n
i
1 7 . 5 ± 1 . 3
9 4 ± 6
0 . 3 5
0 . 2
0 . 7
1 . 4
4 . 3
0 . 4
D i e t e t i c m i l k p o w d e r 1
Z n
h
7 4 . 8 ± 0 . 6
7 2 . 8 ± 1 . 4
9 7 ± 1
0 . 0 2
0 . 5
0 . 6
0 . 6
0 . 9
0 . 1
Z n
i
7 3 . 9 ± 1 . 7
9 9 ± 1
0 . 2 4
0 . 8
1 . 6
1 . 1
2 . 1
0 . 3
Z n
i
7 2 . 7 ± 1 . 3
9 7 ± 1
0 . 0 1
0 . 5
0 . 5
0 . 7
0 . 7
0 . 1
N o n f a t m i l k p o w d e r
Z n
h
4 6 . 1 ± 1 . 1
4 5 . 6 ± 2 . 4
9 9 ± 3
0 . 6 8
0 . 8
2 . 1
1 . 8
4 . 5
0 . 5
Z n
i
4 4 . 1 ± 2 . 4
9 6 ± 3
0 . 1 4
0 . 8
2 . 1
1 . 8
4 . 7
0 . 5
Z n
i
4 5 . 2 ± 2 . 1
9 8 ± 3
0 . 5 1
0 . 8
1 . 8
1 . 7
3 . 9
0 . 4
a
S D e x p r e s s e d a s h a l f o f s t a t e d u n c
e r t a i n t y ( N I S T a n d L G C c e r t i f i e d m a t e r i a l s ) g
i v e n a s 9 5 % c o n f i d e n c e i n t e r v a l .
b
S D e x p r e s s e d a s a r e p r o d u c i b i l i t y S
D ( i n - h o u s e r e f e r e n c e m a t e r i a l s ) c a l c u l a t e d
a c c o r d i n g t o r o b u s t s t a t i s t i c s ( 2 9 ) .
c
U n c e r t a i n t y ( U ) e s t i m a t e d t h r o u g h s i m p l i f i e d a p p r o a c h ( 3 0 , 3 1 ) .
d
S t a t i s t i c e v a l u a t i o n o f r o b u s t t - t e s t :
S a t i s f a c t o r y r e s u l t ( P
> 0 . 0 5 ) ; q u e s t i o n a b l e r
e s u l t ( 0 . 0 1 < P
< 0 . 0 5 ) ; u n s a t i s f a c t o r y r e s u l t
( P
< 0 . 0 1 ) .
e
S D r = S D o f r e p e a t a b i l i t y .
f
S D i R = S D o f i n t e r m e d i a t e r e p r o d u c
i b i l i t y .
g
H o r R a t = R a t i o u s i n g R S D i R a n d H o r w i t z d e n o m i n a t o r a c c o r d i n g t o r e f . 3 2 .
h
R e c o m m e n d e d l i n e f o r I C P - A E S a n a l y s i s .
i
A l t e r n a t e c o n f i r m a t o r y l i n e s f o r I C P
- A E S a n a l y s i s .
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T a b l e
2 0 .
M D 1 – 4 r u g g e d n e s s
t e s t s : a c c u r a c y , p r e c i s i o n , a n d H o r R
a t v a l u e s f o u n d f o r c a l c i u m
i n s i x c e
r t i f i e d a n d i n - h o u s e r e f e r e n c e m a t e r
i a l s u s i n g
r e c o m m e n d e d l i n e s
M a t e r i a l d e s c r i p t i o n
- t e s t c o d e a
R e f e r e n c e
v a l u e , m g / k g
b , c
M e d i a n ,
m g / k g
R e c o v e r y , %
P - v a l u e
d
S D r , m g / k g e
S D i R , m g / k g
f
R S D r ,
%
R
S D i R , %
H o r R a t g
C h o c o l a t e m i l k p o w d e r
M D 1
9 8 7 0 ± 1 2 4
9 9 1 5
1 0 0 ± 1
0 . 9 2
9 1
1 7 1
0 . 9
1 . 7
0 . 3
M D 2
9 9 1 3
1 0 0 ± 2
0 . 9 3
9 7
2 5 0
1 . 0
2 . 5
0 . 4
M D 3
9 6 9 7
9 8 ± 1
0 . 2 0
1 5 5
2 5 0
1 . 6
2 . 6
0 . 5
M D 4
1 0 0 4 2
1 0 1 ± 2
0 . 3 6
6 8
2 1 1
0 . 7
2 . 1
0 . 4
I n f a n t c e r e a l s
M D 1
6 0 0 0 ± 4 4
6 7 5 2
1 1 3 ± 3
0 . 0 0 3
3 3 7
5 2 6
5 . 0
7 . 7
0 . 8
M D 2
6 0 2 7
1 0 0 ± 1
0 . 8 0
1 1 1
2 7 0
1 . 8
4 . 4
0 . 5
M D 3
5 7 6 4
9 6 ± 1
0 . 0 1
8 9
1 4 8
1 . 5
2 . 6
0 . 3
M D 4
5 7 3 1
9 6 ± 2
0 . 0 3
1 5 8
2 7 7
2 . 8
4 . 8
0 . 3
C o r n b r a n
M D 1
4 2 0 ± 1 9
3 7 4
8 9 ± 6
0 . 0 9
1 3
4 6
3 . 3
1 2 . 2
1 . 3
M D 2
4 0 5
9 6 ± 6
0 . 5 5
7
4 4
1 . 6
1 1 . 0
1 . 2
M D 3
4 1 1
9 8 ± 5
0 . 7 1
4
3 7
1 . 1
8 . 9
1 . 0
M D 4
3 1 3
7 5 ± 5
0 . 0 0 2
9
5 1
2 . 8
1 6 . 1
1 . 7
D i e t e t i c m i l k p o w d e r 1
M D 1
3 0 2 0 ± 1 5
3 0 6 2
1 0 1 ± 1
0 . 0 7
3 3
4 3
1 . 1
1 . 4
0 . 2
M D 2
3 0 3 1
1 0 0 ± 1
0 . 7 7
2 6
9 5
0 . 9
3 . 1
0 . 5
M D 3
2 9 5 8
9 8 ± 2
0 . 2 3
3 0
1 3 0
1 . 0
4 . 4
0 . 7
M D 4
2 9 8 6
9 9 ± 1
0 . 2 1
4 3
6 6
1 . 4
2 . 2
0 . 3
P e t f o o d
M D 1
6 1 9 0 ± 1 4 0
6 3 6 5
1 0 3 ± 2
0 . 2 9
8 3
1 4 4
1 . 3
2 . 3
0 . 4
M D 2
6 4 5 7
1 0 4 ± 3
0 . 1 5
8 0
2 2 6
1 . 2
3 . 5
0 . 6
M D 3
6 1 9 8
1 0 0 ± 3
0 . 9 6
1 5 1
2 5 1
2 . 4
4 . 1
0 . 7
M D 4
6 3 8 4
1 0 3 ± 3
0 . 2 5
1 7 6
2 1 0
2 . 7
3 . 0
0 . 5
N o n f a t m i l k p o w d e r
M D 1
1 3 0 0 0 ± 2 5 0
1 3 0 1 2
1 0 0 ± 2
0 . 9 7
9 3
1 9 2
0 . 7
1 . 5
0 . 3
M D 2
1 2 9 3 1
1 0 0 ± 2
0 . 8 1
1 7 0
3 7 7
1 . 3
2 . 9
0 . 5
M D 3
1 2 6 1 2
9 7 ± 2
0 . 1 7
1 1 3
2 2 0
0 . 9
1 . 7
0 . 3
M D 4
1 2 8 4 5
9 9 ± 2
0 . 5 7
1 5 7
2 5 7
1 . 2
2 . 0
0 . 4
a
R u g g e d n e s s t e s t u s i n g d i f f e r e n t m i c r o w a v e d i g e s t i o n s y s t e m s a n d I C P - A E S e q
u i p m e n t ( T a b l e 1 ) .
b
S D e x p r e s s e d a s h a l f o f s t a t e d u n c
e r t a i n t y ( N I S T a n d L G C c e r t i f i e d m a t e r i a l s ) g
i v e n a s 9 5 % c o n f i d e n c e i n t e r v a l .
c
S D e x p r e s s e d a s a r e p r o d u c i b i l i t y S
D ( i n - h o u s e r e f e r e n c e m a t e r i a l s ) c a l c u l a t e d
a c c o r d i n g t o r o b u s t s t a t i s t i c s ( 2 9 ) .
d
S t a t i s t i c e v a l u a t i o n o f r o b u s t t - t e s t :
S a t i s f a c t o r y r e s u l t ( P
> 0 . 0 5 ) ; q u e s t i o n a b l e r
e s u l t ( 0 . 0 1 < P
< 0 . 0 5 ) ; u n s a t i s f a c t o r y r e s u l t
( P
< 0 . 0 1 ) .
e
S D r = S D o f r e p e a t a b i l i t y .
f
S D i R = S D o f i n t e r m e d i a t e r e p r o d u c
i b i l i t y .
g
H o r R a t = R a t i o u s i n g R S D i R a n d H o r w i t z d e n o m i n a t o r a c c o r d i n g t o r e f . 3 2 .
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T a b l e
2 1 .
M D 1 – 4 r u g g e d n e s s
t e s t s : a c c u r a c y , p r e c i s i o n , a n d H o r R
a t v a l u e s f o u n d f o r c o p p e r i n t h r e e c e r t i f i e d a n d i n - h o u s e r e f e r e n c e m a t e r i a l s u s i n g
r e c o m m e n d e d l i n e s
M a t e r i a l d e s c r i p t i o n
- t e s t c o d
e a
R e f e r e n c e
v a l u e , m g / k g
b , c
M e d i a n ,
m g / k g
R e c o v e r y , %
P - v a l u e
d
S D r , m g / k g
e
S D i R , m g / k g
f
R S D r ,
%
R
S D i R , %
H o r R a t g
C o r n b r a n
M D 1
2 . 4 7 ± 0 . 2 0
2 . 3 9
9 7 ± 9
0 . 7 4
0 . 0 6
0 . 3 2
2 . 7
1 3 . 1
0 . 7
M D 2
2 . 3 9
9 7 ± 1 1
0 . 7 8
0 . 0 6
0 . 5 5
2 . 5
2 2 . 9
1 . 2
M D 3
2 . 2 7
9 2 ± 8
0 . 3 2
0 . 0 7
0 . 1 7
3 . 0
7 . 5
0 . 4
M D 4
2 . 4 7
1 0 0 ± 1 0
0 . 9 9
0 . 1 1
0 . 1 2
4 . 3
4 . 7
0 . 2
D i e t e t i c m i l k p o w d e r 1
M D 1
7 . 5 5 ± 0 . 1 3
7 . 7 3
1 0 2 ± 2
0 . 2 9
0 . 3 3
0 . 4 0
4 . 3
5 . 3
0 . 3
M D 2
7 . 5 9
1 0 1 ± 2
0 . 8 3
0 . 0 6
0 . 3 5
0 . 8
4 . 6
0 . 3
M D 3
7 . 6 1
1 0 1 ± 2
0 . 7 6
0 . 1 0
0 . 3 5
1 . 3
4 . 6
0 . 3
M D 4
7 . 7 9
1 0 3 ± 2
0 . 2 0
0 . 3 0
0 . 3 8
3 . 9
5 . 0
0 . 3
N o n f a t m i l k p o w d e r
M D 1
0 . 7 0 ± 0 . 0 5
0 . 5 2
7 4 ± 2 0
0 . 2 3
0 . 0 8
0 . 4 1
1 3 . 1
6 7 . 6
2 . 7
M D 2
0 . 5 9
8 4 ± 2 1
0 . 4 6
0 . 0 4
0 . 3 9
6 . 0
6 7 . 0
2 . 8
M D 3
0 . 4 7
6 7 ± 8
0 . 0 0 4
0 . 0 6
0 . 1 3
1 2 . 8
2 9 . 6
1 . 2
M D 4
0 . 7 4
1 0 5 ± 2 7
0 . 8 5
0 . 1 3
0 . 5 2
1 8 . 9
7 3 . 6
3 . 1
a
R u g g e d n e s s t e s t u s i n g d i f f e r e n t m i c r o w a v e d i g e s t i o n s y s t e m s a n d I C P - A E S e q
u i p m e n t ( T a b l e 1 ) .
b
S D e x p r e s s e d a s h a l f o f s t a t e d u n c
e r t a i n t y ( N I S T a n d L G C c e r t i f i e d m a t e r i a l s ) g
i v e n a s 9 5 % c o n f i d e n c e i n t e r v a l .
c
S D e x p r e s s e d a s a r e p r o d u c i b i l i t y S
D ( i n - h o u s e r e f e r e n c e m a t e r i a l s ) c a l c u l a t e d
a c c o r d i n g t o r o b u s t s t a t i s t i c s ( 2 9 ) .
d
S t a t i s t i c e v a l u a t i o n o f r o b u s t t - t e s t :
S a t i s f a c t o r y r e s u l t ( P
> 0 . 0 5 ) ; q u e s t i o n a b l e r
e s u l t ( 0 . 0 1 < P
< 0 . 0 5 ) ; u n s a t i s f a c t o r y r e s u l t
( P
< 0 . 0 1 ) .
e
S D r = S D o f r e p e a t a b i l i t y .
f
S D i R = S D o f i n t e r m e d i a t e r e p r o d u c
i b i l i t y .
g
H o r R a t = R a t i o u s i n g R S D i R a n d H o r w i t z d e n o m i n a t o r a c c o r d i n g t o r e f . 3 2 .
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1506 POITEVIN ET AL.: JOURNAL OF AOAC I NTERNATIONAL VOL. 92, NO. 5, 2009
T a b l e
2 2 .
M D 1 – 4 r u g g e d n e s s
t e s t s : a c c u r a c y , p r e c i s i o n , a n d H o r R
a t v a l u e s f o u n d f o r i r o n i n f o u r c e r t i f i e d a n d i n - h o u s e r e f e r e n c e m a t e r i a l s u s i n g r e c o m m e n d e d
l i n e s
M a t e r i a l d e s c r i p t i o n
- t e s t c o d e a
R e f e r e n c e
v a l u e , m g / k g
b , c
M e d i a n ,
m g / k g
R
e c o v e r y , %
P - v a l u e
d
S D r , m g / k g e
S D i R , m g / k g
f
R S D r ,
%
R
S D i R , %
H o r R a t g
C h o c o l a t e m i l k p o w d e r
M D 1
1 6 9 . 9 ± 2 . 4
1 6 7 . 7
9 9 ± 2
0 . 4 8
1 . 7
5 . 2
1 . 0
3 . 1
0 . 3
M D 2
1 6 4 . 8
9 7 ± 2
0 . 1 0
1 . 4
3 . 9
0 . 8
2 . 4
0 . 2
M D 3
1 7 3 . 6
1 0 2 ± 2
0 . 2 2
2 . 1
3 . 8
1 . 2
2 . 2
0 . 2
M D 4
1 6 9 . 9
1 0 0 ± 4
0 . 9 9
9 . 3
2 0 . 9
5 . 4
1 2 . 2
1 . 2
I n f a n t c e r e a l s
M D 1
8 0 . 4 ± 0 . 6
7 9 . 9
9 9 ± 2
0 . 7 2
3 . 0
3 . 8
3 . 7
4 . 7
0 . 4
M D 2
7 7 . 8
9 7 ± 1
0 . 0 2
1 . 8
2 . 0
2 . 3
2 . 6
0 . 2
M D 3
7 7 . 7
9 7 ± 2
0 . 0 5
1 . 3
2 . 7
1 . 7
3 . 5
0 . 3
M D 4
7 2 . 8
9 1 ± 2
0 . 0 0 5
3 . 2
5 . 5
4 . 3
7 . 5
0 . 6
C o r n b r a n
M D 1
1 4 . 8 ± 0 . 9
1 2 . 5
8 5 ± 7
0 . 0 5
0 . 3
1 . 8
2 . 6
1 3 . 8
0 . 9
M D 2
1 3 . 9
9 4 ± 6
0 . 3 1
0 . 9
0 . 9
6 . 2
6 . 1
0 . 4
M D 3
1 2 . 4
8 4 ± 6
0 . 0 3
0 . 4
1 . 3
2 . 8
1 0 . 7
0 . 7
M D 4
1 0 . 7
7 2 ± 6
0 . 0 0 2
0 . 5
1 . 7
4 . 9
1 5 . 9
1 . 0
D i e t e t i c m i l k p o w d e r 1
M D 1
5 8 . 5 ± 0 . 4
5 8 . 0
9 9 ± 1
0 . 5 1
0 . 9
1 . 8
1 . 5
3 . 2
0 . 3
M D 2
5 7 . 6
9 8 ± 1
0 . 2 4
0 . 7
1 . 8
1 . 2
3 . 1
0 . 3
M D 3
5 7 . 8
9 9 ± 1
0 . 3 1
1 . 0
1 . 8
1 . 8
3 . 2
0 . 3
M D 4
5 6 . 3
9 6 ± 1
0 . 1 0
0 . 9
1 . 6
1 . 6
2 . 9
0 . 2
a
R u g g e d n e s s t e s t u s i n g d i f f e r e n t m i c r o w a v e d i g e s t i o n s y s t e m s a n d I C P - A E S e q
u i p m e n t ( T a b l e 1 ) .
b
S D e x p r e s s e d a s h a l f o f s t a t e d u n c
e r t a i n t y ( N I S T a n d L G C c e r t i f i e d m a t e r i a l s ) g
i v e n a s 9 5 % c o n f i d e n c e i n t e r v a l .
c
S D e x p r e s s e d a s a r e p r o d u c i b i l i t y S
D ( i n - h o u s e r e f e r e n c e m a t e r i a l s ) c a l c u l a t e d
a c c o r d i n g t o r o b u s t s t a t i s t i c s ( 2 9 ) .
d
S t a t i s t i c e v a l u a t i o n o f r o b u s t t - t e s t :
S a t i s f a c t o r y r e s u l t ( P
> 0 . 0 5 ) ; q u e s t i o n a b l e r
e s u l t ( 0 . 0 1 < P
< 0 . 0 5 ) ; u n s a t i s f a c t o r y r e s u l t ( P
< 0 . 0 1 ) .
e
S D r = S D o f r e p e a t a b i l i t y .
f
S D i R = S D o f i n t e r m e d i a t e r e p r o d u c
i b i l i t y .
g
H o r R a t = R a t i o u s i n g R S D i R a n d H o r w i t z d e n o m i n a t o r a c c o r d i n g t o r e f . 3 2 .
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T a b l e
2 3 .
M D 1 – 4 r u g g e d n e s s
t e s t s : a c c u r a c y , p r e c i s i o n , a n d H o r R
a t v a l u e s f o u n d f o r p o t a s s i u m
i n f i v e c e r t i f i e d a n d i n - h o u s e r e f e r e n c e m a t e r i a l s u s i n g
r e c o m m e n d e d l i n e s
M a t e r i a l d e s c r i p t i o n
- t e s t c o d e a
R e f e r e n c e v a l u e ,
m g / k g
b , c
M e d i a n , m g / k g
R e c o v e r y , %
P - v a l u e
d
S D r , m g / k g e
S D i R , m g / k g
f
R S D r ,
%
R
S D i R , %
H o r R a t g
C h o c o l a t e m i l k p o w d e r
M D 1
9 0 9 0 ± 1 3 3
9 1 4 5
1 0 1 ± 2
0 . 7 3
1 1 5
2 3 7
1 . 3
2 . 6
0 . 5
M D 2
8 9 1 5
9 8 ± 2
0 . 3 4
7 1
3 1 7
0 . 8
3 . 6
0 . 6
M D 3
9 0 2 5
9 9 ± 2
0 . 6 5
6 5
1 3 0
0 . 7
1 . 4
0 . 2
M D 4
9 0 3 1
9 9 ± 2
0 . 6 9
3 9
1 5 3
0 . 4
1 . 7
0 . 3
I n f a n t c e r e a l s
M D 1
6 5 0 0 ± 5 0
6 8 3 0
1 0 5 ± 2
0 . 0 0 6
2 0 0
2 5 0
2 . 9
3 . 7
0 . 6
M D 2
6 4 5 0
9 9 ± 1
0 . 5 6
8 0
1 8 0
1 . 2
2 . 8
0 . 5
M D 3
6 3 6 0
9 8 ± 1
0 . 0 6
5 0
1 2 0
0 . 8
1 . 9
0 . 3
M D 4
6 2 6 0
9 6 ± 1
0 . 0 3
1 0 0
2 1 0
1 . 6
3 . 3
0 . 5
C o r n b r a n
M D 1
5 6 6 ± 3 8
4 6 0
8 1 ± 7
0 . 0 2
1 5
5 9
3 . 3
1 2 . 6
1 . 4
M D 2
4 6 3
8 2 ± 6
0 . 0 2
1 0
4 1
2 . 1
8 . 8
1 . 0
M D 3
5 3 8
9 5 ± 7
0 . 4 8
7
3 5
1 . 4
6 . 3
0 . 7
M D 4
5 6 1
9 9 ± 8
0 . 9 1
1 3
7 3
2 . 4
1 3 . 1
1 . 5
D i e t e t i c m i l k p o w d e r 1
M D 1
5 5 7 0 ± 2 5
5 6 7 8
1 0 2 ± 1
0 . 0 0 7
4 3
5 2
0 . 8
0 . 9
0 . 1
M D 2
5 6 3 3
1 0 1 ± 1
0 . 3 2
6 5
1 5 8
1 . 1
2 . 8
0 . 5
M D 3
5 5 6 1
1 0 0 ± 1
0 . 8 3
3 0
9 9
0 . 5
1 . 8
0 . 3
M D 4
5 6 4 0
1 0 1 ± 1
0 . 0 8
3 2
7 5
0 . 6
1 . 3
0 . 2
N o n f a t m i l k p o w d e r
M D 1
1 6 9 0 0 ± 1 5 0
1 6 6 1 0
9 8 ± 1
0 . 1 0
1 8 0
2 0 0
1 . 1
1 . 2
0 . 5
M D 2
1 6 2 3 0
9 6 ± 1
0 . 0 1
2 2 0
4 5 0
1 . 4
2 . 8
0 . 3
M D 3
1 6 5 8 0
9 8 ± 1
0 . 1 0
8 0
2 5 0
0 . 5
1 . 5
0 . 3
M D 4
1 6 7 3 0
9 9 ± 1
0 . 3 0
2 2 0
2 3 0
1 . 3
1 . 4
0 . 9
a
R u g g e d n e s s t e s t u s i n g d i f f e r e n t m i c r o w a v e d i g e s t i o n s y s t e m s a n d I C P - A E S e q
u i p m e n t ( T a b l e 1 ) .
b
S D e x p r e s s e d a s h a l f o f s t a t e d u n c
e r t a i n t y ( N I S T a n d L G C c e r t i f i e d m a t e r i a l s ) g
i v e n a s 9 5 % c o n f i d e n c e i n t e r v a l .
c
S D e x p r e s s e d a s a r e p r o d u c i b i l i t y S
D ( i n - h o u s e r e f e r e n c e m a t e r i a l s ) c a l c u l a t e d
a c c o r d i n g t o r o b u s t s t a t i s t i c s ( 2 9 ) .
d
S t a t i s t i c e v a l u a t i o n o f r o b u s t t - t e s t :
S a t i s f a c t o r y r e s u l t ( P
> 0 . 0 5 ) ; q u e s t i o n a b l e r
e s u l t ( 0 . 0 1 < P
< 0 . 0 5 ) ; u n s a t i s f a c t o r y r e s u l t
( P
< 0 . 0 1 ) .
e
S D r = S D o f r e p e a t a b i l i t y .
f
S D i R = S D o f i n t e r m e d i a t e r e p r o d u c
i b i l i t y .
g
H o r R a t = R a t i o u s i n g R S D i R a n d H o r w i t z d e n o m i n a t o r a c c o r d i n g t o r e f . 3 2 .
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T a b l e
2 4 .
M D 1 – 4 r u g g e d n e s s
t e s t s : a c c u r a c y , p r e c i s i o n , a n d H o r R
a t v a l u e s f o u n d f o r m a g n e s i u m
i n s i x c e r t i f i e d a n d i n - h o u s e r e f e r e n c e m
a t e r i a l s u s i n g
r e c o m m e n d e d l i n e s
M a t e r i a l d e s c r i p t i o n
- t e s t c o d
e a
R e f e r e n c e v a l u e ,
m g / k g
b , c
M e d i a n , m g / k g
R
e c o v e r y , %
P - v a l u e
d
S D r , m g / k g
e
S D i R , m g / k g
f
R S D r ,
%
R
S D i R , %
H o r R a t g
C h o c o l a t e m i l k p o w d e r
M D 1
1 7 7 9 ± 2 3
1 7 8 2
1 0 0 ± 2
0 . 9 3
1 9
4 2
1 . 0
2 . 4
0 . 3
M D 2
1 7 8 0
1 0 0 ± 2
0 . 9 7
1 8
7 4
1 . 0
4 . 1
0 . 6
M D 3
1 7 8 9
1 0 1 ± 1
0 . 6 9
2 4
2 5
1 . 3
1 . 4
0 . 2
M D 4
1 7 7 0
1 0 0 ± 1
0 . 7 2
1 1
3 3
0 . 6
1 . 8
0 . 2
I n f a n t c e r e a l s
M D 1
8 8 1 ± 8
8 2 7
9 4 ± 1
0 . 0 0 2
2 8
3 2
3 . 4
3 . 9
0 . 5
M D 2
8 9 8
1 0 2 ± 2
0 . 2 9
1 7
3 7
1 . 9
4 . 1
0 . 5
M D 3
9 2 2
1 0 5 ± 1
0 . 0 0 4
2 1
2 2
2 . 2
2 . 4
0 . 3
M D 4
8 9 3
1 0 1 ± 1
0 . 3 3
1 9
2 6
2 . 1
2 . 9
0 . 4
C o r n b r a n
M D 1
8 1 8 ± 3 0
7 7 8
9 5 ± 3
0 . 2 0
9
1 1
1 . 1
1 . 4
0 . 2
M D 2
7 4 9
9 2 ± 3
0 . 0 4
1 4
1 6
1 . 8
2 . 1
0 . 3
M D 3
7 7 8
9 5 ± 4
0 . 2 1
7
1 5
1 . 0
1 . 9
0 . 2
M D 4
7 6 1
9 3 ± 3
0 . 0 8
5
9
0 . 7
1 . 2
0 . 1
D i e t e t i c m i l k p o w d e r 1
M D 1
1 2 0 0 ± 8
1 1 9 1
9 9 ± 1
0 . 2 1
1 3
1 7
1 . 1
1 . 5
0 . 2
M D 2
1 1 9 8
1 0 0 ± 1
0 . 7 9
8
4 4
0 . 7
3 . 7
0 . 5
M D 3
1 2 1 6
1 0 1 ± 1
0 . 2 1
5
1 7
0 . 4
1 . 4
0 . 2
M D 4
1 1 9 3
9 9 ± 1
0 . 4 0
1 2
2 4
1 . 0
2 . 0
0 . 3
P e t f o o d
M D 1
4 8 ± 2
4 6 2
9 6 ± 3
0 . 1 7
7
8
1 . 5
1 . 8
0 . 2
M D 2
4 7 4
9 9 ± 3
0 . 6 7
4
1 4
0 . 9
3 . 0
0 . 3
M D 3
4 7 2
9 8 ± 3
0 . 5 5
6
1 2
1 . 3
2 . 5
0 . 3
M D 4
4 5 6
9 5 ± 3
0 . 1 2
7
2 1
1 . 5
4 . 6
0 . 5
N o n f a t m i l k p o w d e r
M D 1
1 2 0 0 ± 1 5
1 1 8 8
9 9 ± 1
0 . 5 1
1 3
2 5
1 . 1
2 . 1
0 . 3
M D 2
1 1 9 4
1 0 0 ± 2
0 . 8 0
1 4
5 3
1 . 2
4 . 4
0 . 6
M D 3
1 1 8 5
9 9 ± 1
0 . 3 7
9
1 6
0 . 8
1 . 3
0 . 2
M D 4
1 1 7 2
9 8 ± 1
0 . 1 2
1 1
2 1
0 . 9
1 . 8
0 . 2
a
R u g g e d n e s s t e s t u s i n g d i f f e r e n t m i c r o w a v e d i g e s t i o n s y s t e m s a n d I C P - A E S e q
u i p m e n t ( T a b l e 1 ) .
b
S D e x p r e s s e d a s h a l f o f s t a t e d u n c
e r t a i n t y ( N I S T a n d L G C c e r t i f i e d m a t e r i a l s ) g
i v e n a s 9 5 % c o n f i d e n c e i n t e r v a l .
c
S D e x p r e s s e d a s a r e p r o d u c i b i l i t y S
D ( i n - h o u s e r e f e r e n c e m a t e r i a l s ) c a l c u l a t e d
a c c o r d i n g t o r o b u s t s t a t i s t i c s ( 2 9 ) .
d
S t a t i s t i c e v a l u a t i o n o f r o b u s t t - t e s t :
S a t i s f a c t o r y r e s u l t ( P
> 0 . 0 5 ) ; q u e s t i o n a b l e r
e s u l t ( 0 . 0 1 < P
< 0 . 0 5 ) ; u n s a t i s f a c t o r y r e s u l t ( P
< 0 . 0 1 ) .
e
S D r = S D o f r e p e a t a b i l i t y .
f
S D i R = S D o f i n t e r m e d i a t e r e p r o d u c
i b i l i t y .
g
H o r R a t = R a t i o u s i n g R S D i R a n d H o r w i t z d e n o m i n a t o r a c c o r d i n g t o r e f . 3 2 .
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T a b l e
2 5 .
M D 1 – 4 r u g g e d n e s s
t e s t s : a c c u r a c y , p r e c i s i o n , a n d H o r R
a t v a l u e s f o u n d f o r m a n g a n e s e i n t h
r e e c e r t i f i e d a n d i n - h o u s e r e f e r e n c e
m a t e r i a l s u s i n g
r e c o m m e n d e d l i n e s ( M D 1 , M D 2
, M D 3 ) a n d a l t e r n a t e 2 M n I I l i n e ( M D 4 )
M a t e r i a l d e s c r i p t i o n
- t e s t c o d e a
R e f e r e n c e
v a l u e , m g / k g
b , c
M e d i a n , m g / k g
R
e c o v e r y , %
P - v a l u e
d
S D r , m g / k g
e
S D i R , m g / k g
f
R S D r ,
%
R
S D i R , %
H o r R a t g
C o r n b r a n
M D 1
2 . 5 5 ± 0 . 1 5
2 . 3 6
9 3 ± 6
0 . 2 2
0 . 0 3
0 . 0 5
1 . 1
2 . 1
0 . 1
M D 2
2 . 2 7
8 9 ± 5
0 . 0 8
0 . 0 4
0 . 0 8
1 . 9
3 . 5
0 . 2
M D 3
2 . 1 7
8 5 ± 5
0 . 0 2
0 . 0 4
0 . 0 8
2 . 0
3 . 7
0 . 2
M D 4
2 . 3 7
9 3 ± 6
0 . 2 3
0 . 0 3
0 . 0 4
1 . 4
1 . 7
0 . 1
D i e t e t i c m i l k p o w d e r 1
M D 1
1 2 . 7 0 ± 0 . 8 5
1 2 . 4 5
9 8 ± 7
0 . 7 7
0 . 1 6
0 . 1 6
1 . 2
1 . 3
0 . 1
M D 2
1 2 . 3 1
9 7 ± 7
0 . 6 5
0 . 1 2
0 . 2 2
0 . 9
1 . 7
0 . 1
M D 3
1 1 . 7 1
9 2 ± 6
0 . 2 5
0 . 1 2
0 . 2 2
1 . 0
1 . 8
0 . 1
M D 4
1 2 . 7 7
1 0 1 ± 7
0 . 9 3
0 . 1 6
0 . 1 4
1 . 2
1 . 1
0 . 1
N o n f a t m i l k p o w d e r
M D 1
0 . 2 6 ± 0 . 0 3
0 . 2 2
8 5 ± 1 0
0 . 1 8
0 . 0 1
0 . 0 2
4 . 5
8 . 3
0 . 3
M D 2
0 . 2 3
9 0 ± 1 1
0 . 3 7
0 . 0 1
0 . 0 2
4 . 9
6 . 9
0 . 2
M D 3
0 . 3 1
1 1 8 ± 1 4
0 . 2 5
0 . 0 2
0 . 0 3
6 . 7
9 . 7
0 . 4
M D 4
0 . 2 1
8 2 ± 1 0
0 . 1 0
0 . 0 1
0 . 0 1
4 . 8
4 . 3
0 . 2
a
R u g g e d n e s s t e s t u s i n g d i f f e r e n t m i c r o w a v e d i g e s t i o n s y s t e m s a n d I C P - A E S e q
u i p m e n t ( T a b l e 1 ) .
b
S D e x p r e s s e d a s h a l f o f s t a t e d u n c
e r t a i n t y ( N I S T a n d L G C c e r t i f i e d m a t e r i a l s ) g
i v e n a s 9 5 % c o n f i d e n c e i n t e r v a l .
c
S D e x p r e s s e d a s a r e p r o d u c i b i l i t y S
D ( i n - h o u s e r e f e r e n c e m a t e r i a l s ) c a l c u l a t e d
a c c o r d i n g t o r o b u s t s t a t i s t i c s ( 2 9 ) .
d
S t a t i s t i c e v a l u a t i o n o f r o b u s t t - t e s t :
S a t i s f a c t o r y r e s u l t ( P
> 0 . 0 5 ) ; q u e s t i o n a b l e r
e s u l t ( 0 . 0 1 < P
< 0 . 0 5 ) ; u n s a t i s f a c t o r y r e s u l t
( P
< 0 . 0 1 ) .
e
S D r = S D o f r e p e a t a b i l i t y .
f
S D i R = S D o f i n t e r m e d i a t e r e p r o d u c
i b i l i t y .
g
H o r R a t = R a t i o u s i n g R S D i R a n d H o r w i t z d e n o m i n a t o r a c c o r d i n g t o r e f . 3 2 .
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T a b l e
2 6 .
M D 1 – 4 r u g g e d n e s s
t e s t s : a c c u r a c y , p r e c i s i o n , a n d H o r R
a t v a l u e s f o u n d f o r s o d i u m
i n f i v e c e r t i f i e d a n d i n - h o u s e r e f e r e n c e m a t e r i a l s u s i n g
r e c o m m e n d e d l i n e s
M a t e r i a l d e s c r i p t i o n
- t e
s t c o d e a
R e f e r e n c e
v a l u e , m g / k g
b , c
M e d i a n , m g / k g
R e c o v e r y , %
P - v a l u e
d
S D r , m g / k g e
S D i R , m g / k g
f
R S D r ,
%
R S D i R , %
H o r R a t g
C h o c o l a t e m i l k p o w d e r
M D 1
1 9 9 0 ± 4 2
2 0 2 9
1 0 2 ± 2
0 . 4 3
3 1
5 9
1 . 5
2 . 9
0 . 4
M D 2
2 0 0 0
1 0 1 ± 3
0 . 8 6
4 2
9 9
2 . 1
4 . 9
0 . 7
M D 3
1 9 8 1
1 0 0 ± 2
0 . 8 5
2 9
6 8
1 . 5
3 . 4
0 . 5
M D 4
1 9 4 9
9 8 ± 2
0 . 3 6
1 4
3 4
0 . 7
1 . 7
0 . 2
I n f a n t c e r e a l s
M D 1
1 0 5 0 ± 1 4
1 1 0 5
1 0 5 ± 3
0 . 1 2
5 3
8 9
4 . 8
8 . 1
1 . 0
M D 2
1 0 0 2
9 5 ± 2
0 . 0 4
2 1
4 2
2 . 1
4 . 2
0 . 5
M D 3
9 7 0
9 2 ± 3
0 . 0 1
1 2
5 9
1 . 3
6 . 1
0 . 8
M D 4
9 3 5
8 9 ± 3
0 . 0 0 2
2 3
6 3
2 . 5
6 . 8
0 . 8
C o r n b r a n
M D 1
4 3 0 ± 1 6
3 9 5
9 2 ± 3
0 . 0 5
4
1 0
1 . 1
2 . 4
0 . 3
M D 2
3 9 5
9 2 ± 4
0 . 0 8
4
2 7
1 . 1
6 . 8
0 . 7
M D 3
3 9 1
9 1 ± 5
0 . 0 9
1 0
4 0
2 . 5
1 . 0
0 . 1
M D 4
3 8 8
9 0 ± 4
0 . 0 3
4
1 9
1 . 0
5 . 0
0 . 5
D i e t e t i c m i l k p o w d e r 1
M D 1
4 9 2 0 ± 3 0
4 8 5 0
9 9 ± 1
0 . 0 9
4 3
6 9
0 . 9
1 . 4
0 . 2
M D 2
4 8 7 0
9 9 ± 1
0 . 3 1
4 0
1 1 0
0 . 8
2 . 4
0 . 4
M D 3
4 9 1 0
1 0 0 ± 1
0 . 8 1
3 2
1 2 2
0 . 6
2 . 5
0 . 4
M D 4
5 0 0 0
1 0 2 ± 1
0 . 0 9
3 9
7 7
0 . 8
1 . 5
0 . 2
N o n f a t m i l k p o w d e r
M D 1
4 9 7 0 ± 5 0
4 8 9 0
9 8 ± 1
0 . 1 5
6 6
7 1
1 . 3
1 . 4
0 . 2
M D 2
4 9 4 0
9 9 ± 1
0 . 6 0
6 2
1 0 6
1 . 3
2 . 2
0 . 4
M D 3
4 8 1 0
9 7 ± 1
0 . 0 2
6 6
9 8
1 . 4
2 . 0
0 . 3
M D 4
4 9 3 0
9 9 ± 1
0 . 5 1
7 5
1 1 0
1 . 5
2 . 2
0 . 4
a
R u g g e d n e s s t e s t u s i n g d i f f e r e n t m i c r o w a v e d i g e s t i o n s y s t e m s a n d I C P - A E S e q
u i p m e n t ( T a b l e 1 ) .
b
S D e x p r e s s e d a s h a l f o f s t a t e d u n c
e r t a i n t y ( N I S T a n d L G C c e r t i f i e d m a t e r i a l s ) g
i v e n a s 9 5 % c o n f i d e n c e i n t e r v a l .
c
S D e x p r e s s e d a s a r e p r o d u c i b i l i t y S
D ( i n - h o u s e r e f e r e n c e m a t e r i a l s ) c a l c u l a t e d
a c c o r d i n g t o r o b u s t s t a t i s t i c s ( 2 9 ) .
d
S t a t i s t i c e v a l u a t i o n o f r o b u s t t - t e s t :
S a t i s f a c t o r y r e s u l t ( P
> 0 . 0 5 ) ; q u e s t i o n a b l e r
e s u l t ( 0 . 0 1 < P
< 0 . 0 5 ) ; u n s a t i s f a c t o r y r e s u l t
( P
< 0 . 0 1 ) .
e
S D r = S D o f r e p e a t a b i l i t y .
f
S D i R = S D o f i n t e r m e d i a t e r e p r o d u c
i b i l i t y .
g
H o r R a t = R a t i o u s i n g R S D i R a n d H o r w i t z d e n o m i n a t o r a c c o r d i n g t o r e f . 3 2 .
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T a b l e
2 7 .
M D 1 – 4 r u g g e d n e s s
t e s t s : a c c u r a c y , p r e c i s i o n , a n d H o r R
a t v a l u e s f o u n d f o r p h o s p h o r u s i n s
i x c e r t i f i e d a n d i n - h o u s e r e f e r e n c e m
a t e r i a l s u s i n g
r e c o m m e n d e d l i n e s
M a t e r i a l d e s c r i p t i o n
- t e s t c
o d e a
R e f e r e n c e
v a l u e , m g / k g
b , c
M e d i a n ,
m g / k g
R e c o v e r y , %
P - v a l u e
d
S D r , m g / k
g e
S D i R , m g / k g
f
R S D r ,
%
R
S D i R , %
H o r R a t g
C h o c o l a t e m i l k p o w d e r
M D
1
4 0 8 0 ± 3 0
4 1 1 0
1 0 1 ± 1
0 . 6 1
5 1
1 3 2
1 . 3
3 . 2
0 . 5
M D
2
4 1 5 0
1 0 2 ± 1
0 . 2 8
6 2
1 5 0
1 . 5
3 . 6
0 . 6
M D
3
4 1 4 0
1 0 1 ± 1
0 . 1 4
3 0
4 9
0 . 7
1 . 2
0 . 2
M D
4
4 1 7 0
1 0 2 ± 1
0 . 0 7
3 6
8 6
0 . 9
2 . 0
0 . 3
I n f a n t c e r e a l s
M D
1
4 3 0 ± 2 1
4 4 1 8
1 0 2 ± 1
0 . 1 0
1 0 1
1 5 5
2 . 3
3 . 5
0 . 5
M D
2
4 5 0 8
1 0 4 ± 1
0 . 0 1
7 5
1 6 1
1 . 7
3 . 6
0 . 6
M D
3
4 3 8 4
1 0 2 ± 1
0 . 1 0
5 7
8 7
1 . 3
2 . 0
0 . 3
M D
4
4 3 2 1
1 0 0 ± 1
0 . 9 7
7 7
9 7
1 . 8
2 . 3
0 . 4
C o r n b r a n
M D
1
1 7 1 ± 6
1 5 1
8 8 ± 6
0 . 0 6
4
2 3
2 . 7
1 5 . 1
1 . 4
M D
2
1 6 3
9 5 ± 6
0 . 4 5
4
2 4
2 . 4
1 5
1 . 4
M D
3
1 6 9
9 9 ± 4
0 . 3 0
2
9
1 . 0
5 . 3
0 . 5
M D
4
1 1 6
6 8 ± 6
0 . 0 0 1
4
2 7
3 . 3
2 3 . 4
2 . 1
D i e t e t i c m i l k p o w d e r 1
M D
1
3 0 8 0 ± 1 1
3 0 9 5
1 0 1 ± 1
0 . 4 1
2 9
4 4
0 . 9
1 . 4
0 . 2
M D
2
3 1 7 0
1 0 3 ± 1
0 . 0 8
2 7
1 2 3
0 . 8
3 . 9
0 . 6
M D
3
3 1 3 3
1 0 2 ± 1
0 . 0 6
1 7
6 1
0 . 5
1 . 9
0 . 3
M D
4
3 1 1 1
1 0 1 ± 1
0 . 2 1
4 5
6 7
1 . 4
2 . 2
0 . 3
P e t f o o d
M D
1
4 5 1 0 ± 4 0
4 4 9
1 0 0 ± 1
0 . 6 0
2 8
4 9
0 . 6
1 . 1
0 . 2
M D
2
4 6 4
1 0 3 ± 1
0 . 1 1
3 0
1 7 3
0 . 6
3 . 7
0 . 6
M D
3
4 5 4
1 0 1 ± 1
0 . 5 6
3 6
7 8
0 . 8
1 . 7
0 . 3
M D
4
4 5 3
1 0 1 ± 1
0 . 6 0
6 6
8 4
1 . 4
1 . 9
0 . 3
N o n f a t m i l k p o w d e r
M D
1
1 0 6 0 0 ± 1 0 0
1 0 5 9
1 0 0 ± 1
0 . 9 0
1 0 9
1 3 6
1 . 0
1 . 3
0 . 2
M D
2
1 0 8 8
1 0 3 ± 2
0 . 1 2
1 5 6
3 6 7
1 . 4
3 . 4
0 . 6
M D
3
1 0 4 4
9 9 ± 1
0 . 2 0
8 1
1 5 3
0 . 8
1 . 5
0 . 3
M D
4
1 0 4 0
9 8 ± 1
0 . 1 2
6 6
1 7 6
0 . 6
1 . 7
0 . 3
a
R u g g e d n e s s t e s t u s i n g d i f f e r e n t m i c r o w a v e d i g e s t i o n s y s t e m s a n d I C P - A E S e q
u i p m e n t ( T a b l e 1 ) .
b
S D e x p r e s s e d a s h a l f o f s t a t e d u n c
e r t a i n t y ( N I S T a n d L G C c e r t i f i e d m a t e r i a l s ) g
i v e n a s 9 5 % c o n f i d e n c e i n t e r v a l .
c
S D e x p r e s s e d a s a r e p r o d u c i b i l i t y S
D ( i n - h o u s e r e f e r e n c e m a t e r i a l s ) c a l c u l a t e d
a c c o r d i n g t o r o b u s t s t a t i s t i c s ( 2 9 ) .
d
S t a t i s t i c e v a l u a t i o n o f r o b u s t t - t e s t :
S a t i s f a c t o r y r e s u l t ( P
> 0 . 0 5 ) ; q u e s t i o n a b l e r
e s u l t ( 0 . 0 1 < P
< 0 . 0 5 ) ; u n s a t i s f a c t o r y r e s u l t
( P
< 0 . 0 1 ) .
e
S D r = S D o f r e p e a t a b i l i t y .
f
S D i R = S D o f i n t e r m e d i a t e r e p r o d u c
i b i l i t y .
g
H o r R a t = R a t i o u s i n g R S D i R a n d H o r w i t z d e n o m i n a t o r a c c o r d i n g t o r e f . 3 2 .
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1512 POITEVIN ET AL.: JOURNAL OF AOAC I NTERNATIONAL VOL. 92, NO. 5, 2009
T a b l e
2 8 .
M D 1 – 4 r u g g e d n e s s
t e s t s : a c c u r a c y , p r e c i s i o n , a n d H o r R
a t v a l u e s f o u n d f o r z i n c i n t h r e e c e r t i f i e d a n d i n - h o u s e r e f e r e n c e m a t e r i a
l s u s i n g r e c o m m e n d e d
l i n e s ( M D 1 , M D 2 , M D 3 ) a n d a l t e
r n a t e 2 Z n I l i n e ( M D 4 )
M a t e r i a l d e s c r i p t i o n
- t e s t c o
d e a
R e f e r e n c e
v a l u e , m g / k g
b , c
M e d i a n ,
m g / k g
R
e c o v e r y , %
P - v a l u e
d
S D r , m g / k g e
S D i R , m g / k g
f
R S D r ,
%
R
S D i R , %
H o r R a t g
C o r n b r a n
M D 1
1 8 . 6 ± 1 . 1
1 7 . 6
9 5 ± 6
0 . 3 8
0 . 2
0 . 5
1 . 1
2 . 8
0 . 2
M D 2
1 7 . 0
9 2 ± 5
0 . 1 7
0 . 2
0 . 3
1 . 4
1 . 7
0 . 1
M D 3
1 7 . 5
9 4 ± 6
0 . 3 8
0 . 5
1 . 4
3 . 1
8 . 3
0 . 6
M D 4
1 8 . 3
9 8 ± 7
0 . 8 3
0 . 8
2 . 4
4 . 5
1 3 . 6
0 . 9
D i e t e t i c m i l k p o w d e r 1
M D 1
7 4 . 8 ± 0 . 6
7 2 . 5
9 7 ± 1
0 . 0 0 6
1 . 1
0 . 9
1 . 5
1 . 3
0 . 1
M D 2
7 2 . 6
9 7 ± 1
0 . 0 3
0 . 6
1 . 8
0 . 9
2 . 4
0 . 2
M D 3
7 5 . 3
1 0 1 ± 3
0 . 7 8
1 . 0
5 . 0
1 . 3
6 . 7
0 . 6
M D 4
7 6 . 3
1 0 2 ± 1
0 . 1 2
1 . 2
1 . 9
1 . 6
2 . 5
0 . 2
N o n f a t m i l k p o w d e r
M D 1
4 6 . 1 ± 1 . 1
4 5 . 6
9 9 ± 2
0 . 6 9
0 . 7
0 . 9
1 . 5
2 . 0
0 . 2
M D 2
4 4 . 8
9 7 ± 2
0 . 2 8
0 . 7
0 . 9
1 . 6
2 . 0
0 . 2
M D 3
4 5 . 1
9 8 ± 2
0 . 3 8
0 . 7
0 . 9
1 . 6
2 . 0
0 . 2
M D 4
4 6 . 4
1 0 1 ± 3
0 . 8 3
0 . 9
2 . 1
1 . 9
4 . 7
0 . 4
a
R u g g e d n e s s t e s t u s i n g d i f f e r e n t m i c r o w a v e d i g e s t i o n s y s t e m s a n d I C P - A E S e q
u i p m e n t ( T a b l e 1 ) .
b
S D e x p r e s s e d a s h a l f o f s t a t e d u n c
e r t a i n t y ( N I S T a n d L G C c e r t i f i e d m a t e r i a l s ) g
i v e n a s 9 5 % c o n f i d e n c e i n t e r v a l .
c
S D e x p r e s s e d a s a r e p r o d u c i b i l i t y S
D ( i n - h o u s e r e f e r e n c e m a t e r i a l s ) c a l c u l a t e d
a c c o r d i n g t o r o b u s t s t a t i s t i c s ( 2 9 ) .
d
S t a t i s t i c e v a l u a t i o n o f r o b u s t t - t e s t :
S a t i s f a c t o r y r e s u l t ( P
> 0 . 0 5 ) ; q u e s t i o n a b l e r
e s u l t ( 0 . 0 1 < P
< 0 . 0 5 ) ; u n s a t i s f a c t o r y r e s u l t
( P
< 0 . 0 1 ) .
e
S D r = S D o f r e p e a t a b i l i t y .
f
S D i R = S D o f i n t e r m e d i a t e r e p r o d u c
i b i l i t y .
g
H o r R a t = R a t i o u s i n g R S D i R a n d H o r w i t z d e n o m i n a t o r a c c o r d i n g t o r e f . 3 2 .
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method for the determination of Ca ranged between 1.1%
(dietetic milk powder) and 3.9% (infant cereals). The RSDR
ranged between 2.9% (chocolate milk powder) and 5.0%
(peanut butter). The HorRat value should not exceed 1.5.
Table 29 shows that the present method has an acceptable
precision for the determination of Ca in all foodstuffs
analyzed with Ca concentration above the estimated QL. The
trueness as z -score (Table 30) is calculated to range from –0.6
(chocolate milk powder) to 0.2 (peanut butter). The resultsindicate that this method can determine, with sufficient
precision, from 9870 to 411 mg/kg.
(b) Copper .—Table 29 presents estimated performance
characteristics of the ICP-AES method for Cu. The RSDr of
the method for the determination of Cu ranged between 1.8%
(wheat gluten) and 5.0% (infant cereals). The RSDR ranged
between 4.4% (wheat gluten) and 12.0% (infant cereals). The
HorRat value should not exceed 1.0. Table 29 shows that the
present method has an acceptable precision for the
determination of Cu in all foodstuffs analyzed with Cu
concentration above or close to the estimated QL. The
trueness, expressed as z -score (Table 30), is calculated to
range from –0.7 (wheat gluten) to 0.03 (peanut butter). The
results indicate that this method can determine, with sufficient
precision, from 6.09 to 1.94 mg/kg.
(c) Iron.—Table 29 presents estimated performance
characteristics of the ICP-AES method for Fe. The RSDr of
the method for the determination of Fe ranged between 1.5%
(infant cereals) and 5.0% (peanut butter). The RSDR ranged
between 4.1% (wheat gluten) and 14.9% (peanut butter). The
HorRat value should not exceed 1.5. Table 29 shows that the
present method has an acceptable precision for the
determination of Fe in all foodstuffs analyzed with Fe
concentration above the estimated QL. The trueness as z -score
(Table 30) is calculated to range from –2.2 (wheat gluten) to0.2 (dietetic milk powder 2). The results indicate that this
method can determine, with sufficient precision, from 169.9
to 16.4 mg/kg.
(d) Potassium.—Table 29 presents estimated
performance characteristics of the ICP-AES method for K.
The RSDr of the method for the determination of K ranged
between 0.9% (dietetic milk powder) and 1.6% (peanut
butter). The RSDR ranged between 1.2% (dietetic milk
powder) and 7.8% (wheat gluten). The HorRat value should
not exceed 1.5. Table 29 shows that the present method has an
acceptable precision for the determination of K in all
foodstuffs analyzed with K concentration above the estimated
QL. The trueness as z -score (Table 30) is calculated to rangefrom –1.8 (wheat gluten) to 0.7 (peanut butter). The results
indicate that this method can determine, with sufficient
precision, from 9090 to 472 mg/kg
(e) Magnesium.—Table 29 presents estimated
performance characteristics of the ICP-AES method for Mg.
The RSDr of the method for the determination of Mg ranged
between 1.2% (dietetic milk powder) and 3.4% (infant
cereals). The RSDR ranged between 2.9% (dietetic milk
powder) and 5.4% (infant cereals). The HorRat value should
not exceed 1.5. Table 29 shows that the present method has an
acceptable precision for the determination of Mg in all
foodstuffs analyzed with Mg concentration above the
estimated QL. The trueness as z -score (Table 30) is calculated
to range from –1.8 (wheat gluten) to 0.6 (peanut butter). The
results indicate that this method can determine, with sufficient
precision, from 1779 to 444 mg/kg.
(f ) Manganese.—Table 29 presents estimated
performance characteristics of the ICP-AES method for Mn.
The RSDr of the method for the determination of Mn ranged
between 1.4% (wheat gluten) and 7.2% (infant cereals). The
RSDR ranged between 6.5% (chocolate milk powder) and
9.2% (infant cereals). The HorRat value should not exceed
1.0. Table 29 shows that the present method has an acceptable
precision for the determination of Mn in all foodstuffs
analyzed with Mn concentration above the estimated QL. The
trueness as z -score (Table 30) is calculated to range from –1.1
(wheat gluten) to 0.1 (dietetic milk powder). The results
indicate that this method can determine, with sufficient
precision, from 16.0 to 0.405 mg/kg.
(g) Sodium.—Table 29 presents estimated performance
characteristics of the ICP-AES method for Na. The RSDr of the method for the determination of Na ranged between 1.2%
(wheat gluten and dietetic milk powder) and 3.9% (infant
cereals). The RSDR ranged between 2.2% (chocolate milk
powder) and 5.5% (infant cereals). The HorRat value should
not exceed 1.0. Table 29 shows that the present method has
an acceptable precision for the determination of Na in all
foodstuffs analyzed with Na concentration above the
estimated QL. The trueness as z -score (Table 30) is calculated
to range from –1.6 (dietetic milk powder and wheat gluten)
to –0.03 (peanut butter). The results indicate that this
method can determine, with sufficient precision, from 4890
to 1420 mg/kg.
(h) Phosphorus.—Table 29 presents estimated
performance characteristics of the ICP-AES method for P.
The RSDr of the method for the determination of P ranged
between 1.2% (wheat gluten) and 2.0% (peanut butter). The
RSDR ranged between 2.1% (infant cereals) and 3.3% (wheat
gluten). The HorRat value should not exceed 1.0. Table 29
shows that the present method has an acceptable precision for
the determination of P in all foodstuffs analyzed with
P concentration above the estimated QL. The trueness as
z -score (Table 30) is calculated to range from –2.0 (wheat
gluten) to 0.8 (peanut butter). The results indicate that this
method can determine, with sufficient precision, from 4320
to 2190 mg/kg.(i) Zinc.—Table 29 presents estimated performance
characteristics of the ICP-AES method for Zn. The RSDr of the
method for the determination of Zn ranged between 1.4%
(wheat gluten) and 3.0% (infant cereals). The RSDR ranged
between 3.8% (infant cereals) and 6.0% (peanut butter). The
HorRat value should not exceed 1.0. Table 29 shows that the
present method has an acceptable precision for the
determination of Zn in all foodstuffs analyzed with Zn
concentration above the estimated QL. The trueness as z -score
(Table 30) is calculated to range from –1.7 (wheat gluten) to 1.1
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T a b l e
2 9 .
E s t i m a t e d p e r f o r m a n c e c h a r a c t e r i s t i c s o f t h e I C P - A E S m
e t h o d f o r d e t e r m i n a t i o n o f n i n e e l e m
e n t s ( C a , C u , F e , K , M g , M n , N a , P , a n d Z n )
S a m p l e d e s c r i p t i o n
R e f e
r e n c e
v a l u e , m g / k g a
M e d i a n , m g / k g
n b
S D
r , m g / k g c
S D R , m g / k g
d
R S D r ,
%
R S D R , %
r , m g / k g e
R , m g / k g
f
H o r R a t g
z - s c o r e
C a l c i u m
P e a n u t b u t t e r
4 1 1
± 1 8
4 1 6
9
1 4
2 1
3 . 3
5 . 0
3 9
5 7
0 . 8
0 . 2
C h o c o l a t e m i l k p o w d e r
9 8 7 0
± 2 4 8
9 7 1 2
9
1 6 2
2 8 0
1 . 7
2 . 9
4 4 8
7 7 5
0 . 7
– 0 . 6
I n f a n t c e r e a l s
6 0 0 0 ± 8 8
5 9 7 2
9
2 3 4
2 9 0
3 . 9
4 . 9
6 4 9
8 0 3
1 . 1
– 0 . 1
D i e t e t i c m i l k p o w d e r 2
5 7 8 0 ± 5 6
5 6 9 6
9
6 1
2 1 8
1 . 1
3 . 8
1 7 0
6 0 6
0 . 9
– 0 . 4
W h e a t g l u t e n
3 6 9
± 3 5
3 6 5
9
5
1 5
1 . 4
4 . 0
1 5
4 1
0 . 6
– 0 . 3
C o p p e r
P e a n u t b u t t e r
4 . 9 3
± 0 . 1 5
4 . 9 4
9
0 . 2 0
0 . 3 1
4 . 1
6 . 2
0 . 5 6
0 . 8 5
0 . 5
0 . 0 3
C h o c o l a t e m i l k p o w d e r
N
A h
5 . 9 2
9
0 . 1 1
0 . 4 1
1 . 9
6 . 9
0 . 3 1
1 . 1 3
0 . 6
I n f a n t c e r e a l s
N A
1 . 9 4
9
0 . 1 0
0 . 2 3
5 . 0
1 2
0 . 2 7
0 . 6 5
0 . 8
D i e t e t i c m i l k p o w d e r 2
6 . 1 0
± 0 . 2 0
6 . 0 9
9
0 . 1 2
0 . 4 0
2 . 0
6 . 5
0 . 3 3
1 . 1 0
0 . 5
– 0 . 0 2
W h e a t g l u t e n
5 . 9 4
± 0 . 7 2
5 . 7 7
9
0 . 1 0
0 . 2 6
1 . 8
4 . 4
0 . 2 9
0 . 7 1
0 . 4
– 0 . 7
I r o n
P e a n u t b u t t e r
1 6 . 4
± 0 . 8
1 5 . 9
9
0 . 8
2 . 4
5 . 0
1 4 . 9
2 . 2
6 . 5
1 . 4
– 0 . 2
C h o c o l a t e m i l k p o w d e r
1 6 9 . 9 ± 4 . 8
1 6 6 . 2
9
3 . 8
7 . 4
2 . 3
4 . 4
1 0 . 5
2 0 . 4
0 . 6
– 0 . 5
I n f a n t c e r e a l s
8 0 . 4
± 1 . 2
7 4 . 8
9
1 . 2
3 . 9
1 . 5
5 . 2
3 . 2
1 0 . 8
0 . 6
– 1 . 4
D i e t e t i c m i l k p o w d e r 2
8 1 . 1
± 1 . 0
8 1 . 9
9
2 . 2
3 . 6
2 . 7
4 . 3
6 . 0
9 . 9
0 . 5
0 . 2
W h e a t g l u t e n
5 4 . 3
± 6 . 8
4 9 . 8
9
1 . 2
2 . 1
2 . 4
4 . 1
3 . 4
5 . 7
0 . 5
– 2 . 2
P o t a s s i u m
P e a n u t b u t t e r
6 0 7 0
± 2 0 0
6 1 5 7
9
1 0 1
1 1 8
1 . 6
1 . 9
2 7 9
3 2 6
0 . 4
0 . 7
C h o c o l a t e m i l k p o w d e r
9 0 9 0
± 2 6 6
9 0 0 6
9
1 0 0
1 6 6
1 . 1
1 . 8
2 7 7
4 6 0
0 . 4
– 0 . 5
I n f a n t c e r e a l s
6 5 0 0
± 1 0 0
6 4 6 6
9
1 0 0
1 2 4
1 . 5
1 . 9
2 7 7
3 4 3
0 . 4
– 0 . 3
D i e t e t i c m i l k p o w d e r 2
6 4 2 0 ± 5 2
6 4 3 1
9
6 1
7 6
0 . 9
1 . 2
1 6 9
2 1 2
0 . 3
0 . 1
W h e a t g l u t e n
4 7 2
± 6 1
4 1 3
9
6
3 2
1 . 5
7 . 8
1 7 . 1
8 9 . 3
1 . 2
– 1 . 8
M a g n e s i u m
P e a n u t b u t t e r
1 6 8 0 ± 7 0
1 7 5 3
9
4 2
1 1 6
2 . 4
6 . 6
1 1 7
3 2 1
1 . 3
0 . 6
C h o c o l a t e m i l k p o w d e r
1 7 7 9 ± 4 6
1 7 5 1
9
3 3
5 4
1 . 9
3 . 1
9 1 . 7
1 5 1
0 . 6
– 0 . 5
I n f a n t c e r e a l s
8 8 1
± 1 6
8 6 0
9
2 9
4 7
3 . 4
5 . 4
8 1
1 2 9
0 . 9
– 0 . 5
D i e t e t i c m i l k p o w d e r 2
4 4 4 ± 5
4 4 1
9
5 . 4
1 2 . 7
1 . 2
2 . 9
1 5 . 0
3 5 . 3
0 . 5
– 0 . 2
W h e a t g l u t e n
5 1 0
± 4 7
4 8 3
9
1 0
1 5
2 . 0
3 . 1
2 6
4 1
0 . 5
– 1 . 8
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T a b l e
2 9 .
( c o n t i n u e d )
S a m p l e d e s c r i p t i o n
R e f e
r e n c e
v a l u e , m g / k g a
M e d i a n ,
m g / k g
n b
S D
r , m g / k g c
S D R , m g / k g
d
R S D r ,
%
R S D R , %
r , m g / k g e
R , m g / k g
f
H o r R a t g
z - s c o r e
M a n g a n e s e
P e a n u t b u t t e r
1 6 . 0
± 0 . 6
1 6 . 0
9
0 . 4
1 . 3
2 . 4
7 . 8
1 . 1
3 . 5
0 . 7
0 . 0
C h o c o l a t e m i l k p o w d e r
N A
7 . 5 3
9
0 . 1 5
0 . 4 9
2 . 1
6 . 5
0 . 4 3
1 . 3 6
0 . 6
I n f a n t c e r e a l s
N A
1 6 . 5
9
1 . 2
1 . 5
7 . 2
9 . 2
3 . 3
4 . 2
0 . 9
D i e t e t i c m i l k p o w d e r 2
0 . 4 0 5
± 0 . 0 3 4
0 . 4 0 7
9
0 . 0 0 7
0 . 0 2 9
1 . 7
7 . 1
0 . 0 2 0
0 . 0 8 0
0 . 4
0 . 1
W h e a t g l u t e n
1 4 . 3
± 0 . 8
1 3 . 0
9
0 . 2
1 . 2
1 . 4
9 . 1
0 . 5
3 . 3
0 . 8
– 1 . 1
S o d i u m
P e a n u t b u t t e r
4 8 9 0
± 1 4 0
4 8 8 6
9
1 2 9
1 2 2
2 . 6
2 . 5
3 5 8
3 3 7
0 . 6
0 . 0 3
C h o c o l a t e m i l k p o w d e r
1 9 9 0 ± 8 4
1 9 3 7
9
2 8
4 2
1 . 4
2 . 2
7 7
1 1 7
0 . 4
– 1 . 3
I n f a n t c e r e a l s
1 0 5 0 ± 2 8
9 9 7
9
3 9
5 5
3 . 9
5 . 5
1 0 7
1 5 2
1 . 0
– 1 . 0
D i e t e t i c m i l k p o w d e r 2
1 8 4 0 ± 2 0
1 7 6 7
9
2 2
4 6
1 . 2
2 . 6
6 0
1 2 8
0 . 5
– 1 . 6
W h e a t g l u t e n
1 4 2 0
± 1 1 0
1 3 5 3
9
1 7
4 1
1 . 2
3 . 0
4 7
1 1 2
0 . 6
– 1 . 6
P h o s p h o r u s
P e a n u t b u t t e r
3 3 7 8 ± 9 2
3 4 4 6
9
7 0
8 8
2 . 0
2 . 5
1 9 3
2 4 3
0 . 5
0 . 8
C h o c o l a t e m i l k p o w d e r
4 0 8 0 ± 6 0
4 1 2 7
9
7 0
1 2 3
1 . 7
3 . 0
1 9 4
3 4 1
0 . 7
0 . 4
I n f a n t c e r e a l s
4 3 2 0 ± 4 2
4 3 0 2
9
5 8
9 1
1 . 3
2 . 1
1 6 0
2 5 3
0 . 5
– 0 . 2
D i e t e t i c m i l k p o w d e r 2
3 7 2 0 ± 2 4
3 7 6 0
9
5 2
1 2 2
1 . 4
3 . 2
1 4 4
3 3 8
0 . 7
0 . 3
W h e a t g l u t e n
2 1 9 0
± 1 5 0
2 0 5 3
9
2 5
6 8
1 . 2
3 . 3
6 9
1 8 9
0 . 7
– 2 . 0
Z i n c
P e a n u t b u t t e r
2 6 . 3
± 1 . 1
2 6 . 8
9
0 . 6
1 . 6
2 . 4
6 . 0
1 . 8
4 . 5
0 . 6
0 . 3
C h o c o l a t e m i l k p o w d e r
N A
1 8 . 5
9
0 . 4
0 . 9
2 . 1
4 . 8
1 . 1
2 . 5
0 . 5
I n f a n t c e r e a l s
N A
3 6 . 7
9
1 . 1
1 . 4
3 . 0
3 . 8
3 . 1
3 . 8
0 . 4
D i e t e t i c m i l k p o w d e r 2
5 1 . 0
± 0 . 8
5 3 . 6
9
1 . 3
2 . 4
2 . 4
4 . 5
3 . 6
6 . 6
0 . 5
1 . 1
W h e a t g l u t e n
5 3 . 8
± 3 . 7
4 9 . 9
9
0 . 7
2 . 3
1 . 4
4 . 5
2 . 0
6 . 3
0 . 5
– 1 . 7
a
E x p a n d e d u n c e r t a i n t y e x p r e s s e d a s u n c e r t a i n t y w i t h a c o v e r a g e f a c t o r o f 2 .
b
n = N u m b e r o f l a b o r a t o r i e s .
c
S D r = R e p e a t a b i l i t y S D .
d
S D R = R e p r o d u c i b i l i t y S D .
e
r = R e p e a t a b i l i t y l i m i t .
f
R = R e p r o d u c i b i l i t y l i m i t .
g
H o r R a t v a l u e a s r a t i o u s i n g R S D R a n d H o r w i t z d e n o m i n a t o r a c c o r d i n g t o r e f . 3 2
.
h
N A = N o t a v a i l a b l e .
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1516 POITEVIN ET AL.: JOURNAL OF AOAC I NTERNATIONAL VOL. 92, NO. 5, 2009
T a b l e
3 0 .
S t a t i s t i c a l a n a l y s i s
o f n i n e e l e m e n t s d e t e r m i n e d i n f o o d
p r o d u c t s t e s t e d b y I C P - A E S
S t a t i s t i c
C a
C u
F e
K
M g
M n
N a
P
Z n
P e a n u t b u t t e r
F o u n d m e a n l e v e l , m g / k g
4 1 6
4 . 9 4
1 5 . 9
6 1 5 7
1 7 5 3
1 6 . 0
4 8 8 6
3 4 4 6
2 6 . 8
C e r t i f i e d v a l u e , m g / k g
4 1 1
4 . 9 3
1 6 . 4
6 0 7 0
1 6 8 0
1 6 . 0
4 8 9 0
3 3 7 8
2 6 . 3
S D R , m g / k g
2 1
0 . 3 1
2 . 4
1 1 8
1 1 6
1 . 3
1 2 2
8 8
1 . 6
z - s c o r e
0 . 2
0 . 0 3
– 0 . 2
0 . 7
0 . 6
0
– 0 . 0 3
0 . 8
0 . 3
C h o c o l a t e m i l k p o w d e r
F o u n d m e a n l e v e l , m g / k g
9 7 1 2
5 . 9 2
1 6 6 . 2
9 0 0 6
1 7 5 1
7 . 5 3
1 9 3 7
4 1 2 7
1 8 . 5
C e r t i f i e d v a l u e , m g / k g
9 8 7 0
N A a
1 6 9 . 9
9 0 9 0
1 7 7 9
N A
1 9 9 0
4 0 8 0
N A
S D R , m g / k g
2 8 0
0 . 4 1
7 . 4
1 6 6
5 4
0 . 4 9
4 2
1 2 3
0 . 9
z - s c o r e
– 0 . 6
– 0 . 5
– 0 . 5
– 0 . 5
– 1 . 3
0 . 4
I n f a n t c e r e a l s
F o u n d m e a n l e v e l , m g / k g
5 9 7 2
1 . 9 4
7 4 . 8
6 4 6 6
8 6 0
1 6 . 5
9 9 7
4 3 0 2
3 6 . 7
C e r t i f i e d v a l u e , m g / k g
6 0 0 0
N A
8 0 . 4
6 5 0 0
8 8 1
N A
1 0 5 0
4
3 2 0
N A
S D R , m g / k g
2 9 0
0 . 2 3
3 . 9
1 2 4
4 7
1 . 5
5 5
9 1
1 . 4
z - s c o r e
– 0 . 1
– 1 . 4
– 0 . 3
– 0 . 5
– 1
– 0 . 2
D i e t e t i c m i l k p o w d e r 2
F o u n d m e a n l e v e l , m g / k g
5 6 9 6
6 . 0 9
8 1 . 9
6 4 3 1
4 4 1
0 . 4 0 7
1 7 6 7
3 7 6 0
5 3 . 6
C e r t i f i e d v a l u e , m g / k g
5 7 8 0
6 . 1
8 1 . 1
6 4 2 0
4 4 4
0 . 4 0 5
1 8 4 0
3 7 2 0
5 1
S D R , m g / k g
2 1 8
0 . 4
3 . 6
7 6
1 3
0 . 0 2 9
4 6
1 2 2
2 . 4
z - s c o r e
– 0 . 4
– 0 . 0 2
0 . 2
0 . 1
– 0 . 2
0 . 1
– 1 . 6
0 . 3
1 . 1
W h e a t g l u t e n
F o u n d m e a n l e v e l , m g / k g
3 6 5
5 . 7 7
4 9 . 8
4 1 3
4 8 3
1 3
1 3 5 3
2
0 5 3
4 9 . 9
C e r t i f i e d v a l u e , m g / k g
3 6 9
5 . 9 4
5 4 . 3
4 7 2
5 1 0
1 4 . 3
1 4 2 0
2 1 9 0
5 3 . 8
S D R , m g / k g
1 5
0 . 2 6
2 . 1
3 2
1 5
1 . 2
4 1
6 8
2 . 3
z - s c o r e
– 0 . 3
– 0 . 7
– 2 . 2
– 1 . 8
– 1 . 8
– 1 . 1
– 1 . 6
– 2
– 1 . 7
a
N A = N o t a v a i l a b l e .
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(dietetic milk powder).The results indicate that this method candetermine, with sufficient precision, from 53.6 to 18.5 mg/kg.
( j) Horwitz equation.—Comparison of the Horwitz
function with that obtained from 45 results (i.e., nine elements
in five matrixes) of the collaborative study highlights
excellent precision as shown in Figure 1. This graph shows
that the trend of data from collaborative study follows the
theoretical Horwitz function, as the slope is similar. The
intercept is significantly different, and hence, this consistent
and constant deviation from predicted HorRat value can be
explained by the excellent experience and training of analysts
(microwave digestion handling/ICP practice) in laboratories
that were also informed of the maximum concentration of
each element in the five matrixes tested.
Conclusions
Method Performance
The MDO and MDC procedures used for SLV and RT
were shown to be effective with acceptable agreement toward
certified and in-house reference values in terms of recovery
for most samples covering the nine sectors of the food
triangle.
This ICP-AES analytical method was proven to be simple,
selective, accurate, and reliable for the determination of Ca,
Cu, Fe, K, Mg, Mn, P, Na, and Zn in most food matrixes.
Recommended and alternate analytical lines corrected byappropriate IS and Cs ion buffer concentration ranging
between 0.1 and 1% (w/v) were validated according the
statistic treatment of selectivity, sensitivity, linearity,
accuracy, and precision through SLV using ICP-AES
equipment with axially viewing plasma after MDC, and
through ruggedness tests using ICP-AES equipment with
radial and dual viewings of the plasma after MDC and MDO
procedures.
Performance characteristics reported for 13 certified and
in-house reference materials covering the triangle foodsectors
fulfilled AOAC criteria and recommendations in terms of accuracy (trueness, recovery, and z -scores) and precision
(repeatability and reproducibility RSDs, HorRat values)
regarding SLV and collaborative study.
The determination of nine nutritional minerals in fortified
foodproducts by ICP-AES is fit-for-purpose according to ISO
17025 norm and AOAC acceptability criteria.
Improvement of AOAC Official Method 984.27
Main improvements compared to the AOAC Method
984.27 are: (1) The use of microwavedigestion systems with a
single acid (nitric acid) for an optimized sample preparation inorder to improve element recoveries from difficult matrixes
and to increase sample throughput, favoring safety
precautions and time-savings for operators in laboratories. It
is a significant improvement regarding long, time-consuming
acid digestion with unsafe acid handling (HNO3/HClO4) used
for AOAC Method 984.27. (2) The use of appropriate
analytical wavelengths for each element of interest and the
automatic addition of a solution of appropriate IS and
ionization buffer to correct for physical and chemical
interferences (i.e., to compensate for matrix effects induced
by the complexity of the food samples). The aim is to improve
short-term accuracy (repeatability) and long-term stability(reproducibility and calibration curve validity in a long
analytical batch). Neither internal standardization nor ion
buffer are used for AOAC Method 984.27. (3) The application
for all food matrixes covering all of the nine AOAC food
triangle sectors, including infant formula, which were the
unique types of matrixes validated for AOAC Method 984.27.
This fully validated multielemental method is
cost-efficient, time-saving, accurate, and fit-for-purpose. It is
proposed as an improved version of AOAC Official Method
984.27 for fortified food products, including infant formula.
POITEVIN ET AL.: JOURNAL OF AOAC I NTERNATIONAL VOL. 92, NO. 5, 2009 1517
Figure 1. Ring trial: Comparison of Horwitz equation and experimental equation found for the ring trial.
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Acknowledgments
We would like to thank Florence Monard and Thierry
Delatour from the Nestlé Research Center for useful
discussions and support given during the work. We are also
indebted to the following collaborators for their skilfull
participation in ruggedness tests MD3, MD4, and the
collaborative study:
Susanna Berger and Rafael Berrocal, PTC, Konolfingen,Switzerland
Ria Bos, Ton Noorlos, and Genevieve Daix, NQAC,
Nunspeet, The Netherlands
Anne Baillon, Christine Senechal, Laure Brullebaut, and
Caroline Gaudin, Creully Factory, Creully, France
Agnes Fortineau, Christian Dekussche, and Christine
Caseiro, Boué Factory, Boué, France
Rick Reba and Genevieve Cole, NQAC, Dublin, OH
Andy Abrahamson, Eau Claire Factory, Eau Claire, WI
Roberto Leal and J. Barrios, SQAL, Macul, Chile
Rey Oliver Mabiog and Ma. Josephine Gonzales, SQAL,
Cabuyao, The Philippines
Gursharan-Singh Dhillon, CQAL, Moga, India
Choo Lee Foon, NQAC, Shah Alam, Malaysia
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