1
Project no.FP6 - 513944
EuroFIR
EUROPEAN FOOD INFORMATION RESOURCE NETWORK
Instrument: Network of Excellence
Thematic Priority: 5 – Food Quality and Safety
D1.3.16 – M37 (by 1/2/08) - Report on evaluation of analytical methods
according with compilers needs 4/5 (Minerals and Trace Elements)
Due date of milestone or deliverable: 1/2/08
Actual submission date: 18/03/08*(available at Technical webside)
Start Date: January 01, 2005 Duration: 5 years
Organisation name of lead contractor for this deliverable or milestone –
INSA – Partner 24
Project co-funded by the European Commission within the Sixth Framework Programme
(2002-2006) Dissemination Level (please check appropriate box)
PU Public
PP Restricted to other programme participants (including the Commission Services)
RE Restricted to a group specified by the consortium (including the Commission Services)
CO Confidential, only for members of the consortium (including the Commission Services) x
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Index
Minerals and Trace Elements ........................................................................................... 3
(i) Copper .............................................................................................. 10
(i) Iron ................................................................................................... 23
(i) Magnesium ....................................................................................... 30
(ii) .......................................................................................................... 30
(i) Phosphorus ....................................................................................... 36
(i) Potassium .......................................................................................... 42
(i) Selenium ........................................................................................... 48
(i) Sodium .............................................................................................. 58
(i) Zinc ................................................................................................... 65
(i)
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Minerals and Trace Elements
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Calcium
Calcium (Ca) belongs to group II of the third period of the Periodic Table of Elements. It has an
atomic weight of 40.08; its atomic number is 20, its valency is 2. It is the fifth most abundant element
in the human body (EFSA, 2003)
Golden Standard
ISO 11885: 2007 Water quality -- Determination of selected elements by inductively coupled
plasma optical emission spectrometry (ICP-OES)
ISO 17294:2003: Water quality -- Application of inductively coupled plasma mass spectrometry
(ICP-MS) -- Part 2: Determination of 62 elements
prEN 15505 Foodstuffs - Determination of trace elements - Determination of sodium,
magnesium by flame atomic absorption spectrometry (AAS) after microwave digestion
AOAC 984.27 – ICP-OES Calcium, Copper, Iron, Magnesium, Manganese, Phosphorus,
Potassium, Sodium, and Zinc in Infant Formula
NMKL no 147 (2003). Magnesium and calcium; determination in foodstuffs using flame atomic
absorption spectrometry after microwave oven digestion.
Scope
Determination of Calcium in foodstuffs in all relevant matrix successfully tested in laboratory
proficiency testing.
Principle
Edible parts are grinder and homogenised in suitable apparatus. The organic matrix are
removed by microwave digestion. The Calcium content is determined by flame atomic
absorption spectrometry-procedures( AAS) or by Inductively coupled plasma atomic emission
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spectroscopy (ICP-AES) also refered as Inductively Coupled Plasma Optical Emission
Spectrometry (ICP-OES).
Key steps
Secção 1.02
Preparation
o The edible part needs to be separate from the foodstuffs ( EN 13804:2002
provide examples of sample preparation from foodstuffs)
Homogenization
o Edible parts are grinder in suitable apparatus (coffee grinder or kitchen
grinder; stainless steel vegetable slice; plastic salad spinner and homogenised;
o To avoid contamination the apparatus equipped with titanium or ceramics
knives, agate mortar or ball mill can be used for size reduction and
homogenisation( EN 13804:2002 is the reference standard for sample
preparation
Separation
Organic matrix are removed or extracted :
o Pressure digestion: The sample dissolved in concentrated acid are digested
in a sealed vessel in a pressure container at high temperature and pressure by
conventional or microwave assisted heating. The method is described for AAS
and ICP OES.
Detection
o The instrumental parameters for flame AAS
Flame: Air acetylene, oxidising
Wavelength 422.7nm
o The instrumental parameters for ICP-OES
Wavelength 315,887 nm; Interferences: Co, Mo Limit of Quantification:
(radial viewing 100 ; axial viewing 13)
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Wavelength 317,933 nm ; Fe, V interferences; Limit of Quantification:
(radial viewing 4 ; axial viewing 26)
Wavelength422,673 nm ; Mo,V, Zr interferences; Limit of Quantification:
(radial viewing 4 ; axial viewing 26)
Quantification
o AAS
After instrument response is stable the linearity, sensitivity and limit of
quantification verified. The content of Calcium in sample is determined
from calibration curve by plotting (absorbance (A) peak area ) against
concentration. The calibration curve is prepared with at least five
points using concentrations of standard solutions within working range.
o ICP OES
After verification of instrument performance (drift; interferences,
background correction). The content of Calcium in sample is
determined from linear regression method using blank, standard
solutions and , internal standards
Criteria for analytical performance and Analytical Quality
control
Method Performance
Table 1. Relevant parameters obtained by EN 15505 inter laboratory studies
Matrix
Parameter
Wheat
Bran
Simulated
diet
Simulated
diet
Milk
powder
Minced
fish
Apple Chocolate
RSD r % 5.5 4.7 4.3 3.6 2.4 7.8 7.3
RSD R% 19 23 15 6.3 5.9 22 20
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Certified Reference Materials/Standard Reference Material
Table 2. List of Available CRM/SRM in 2008
LGC 7104 Sterilized cream
NIST 2384 Baking chocolate(reference value)
LGC 7112 Pig liver Paste
NIST 2387 Peanut Butter
GBW 08552 Freeze dried Pork Muscle
LGC 7000 Beef Pork Meat
NIST 1546 Meat Homogenate(reference
value)
NIST 8415 Whole Egg Powder(reference
value)
BCR 381 Rye Flour
BCR 383 Freeze Dried Green Beans
GBW 07605 Tea
NIST 1567a wheat Flour
NIST 1568a Rice Flour
NIST 2383 Baby Food(reference value)
NIST 8432 Corn Starch (reference value)
NIST 8433 Corn Barn(reference value)
NIST 8436 Durum Wheat Flour(reference
value)
VMA 195 Cereal
VMA 399 Cereal
LGC 7105 Rice Pudding
NIST 1548a Freeze Dried Mixed Diet
NIST 1846 Infant Formula(reference value)
NIST 8435 Whole Milk Powder(reference
value)
LGC 7001 Pork Meat
NIST 1549 Non- Fat Milk Powder
NIST 1566b Freeze Dried Oyster Tissue
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NIST 1570a Freeze Dried Spinach Leaves
NIST 2385 Slurried Spinach
NIST 1946 Fish Tissue(reference value)
LGC 7160 Crabe Paste
NIST 1577b Freeze Dried Bovine liver
NIST 3244 Protein Powder
NIST 8418 wheat gluten (reference value)
Proficiency Testing Schemes (www.eptis.bam.de)
o 26 Providers are register in the database
o Following matrix are registed
Wine, water, animal feeds, diet food, baby food, fruit juice, carbonate
soft drinks, syrup, meat products, plants, milk powder, UHT milk,
cheese processed, sausage boiled, dietary supplements
Other methods available
Table 3. CodexStan 234-1999)- Recommended methods of analysis
Matrix
Method Reference Principle Type
Canned green peas AOAC 968.31 Complexomteric titrimetry II
Canned strawberries AOAC 968.31 Complexometric titrimetry II
Canned tomatoes AOAC 968.31 Complexometric titrimetry II
Citrus marmalade AOAC 968.31 Complexometric titrimetry II
Jams (fruit preserves)
and jellies
AOAC 968.31 Complexometric titrimetry II
Natural mineral waters ISO 6058:1984 Titrimetry II
Natural mineral waters ISO 7980:1986(confirmed
1995)
Atomic absorption
spectrophotometry
III
Special foods AOAC 984.27 ICP emission spectrometry III
Food grade salt ISO 2482:1973 Complexometric titrimetry II
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Compatibility of old data
o All methods give similar results depends on amount of mineral present
(methods have different limits of quantification).
References
Deharveng G., Charrondière UR, Slimani N., Southgate DAT., Riboli E. (1999)
Comparison of nutrients in food composition tables available in the nine European
countries participating in EPIC. European Journal of Clinical Nutrition 53, 60-79
Greenfield H, Southgate DAT (2002). Food Composition Data – Production,
Management and Use. Elsevier Applied Science, London, UK
Pohl, P., & Prusisz, B. (2007). Determination of Ca, Mg, Fe and Zn partitioning in UHT
cow milks by two-column ion exchange and flame atomic absorption spectrometry
detection. Talanta, 71(2), 715–721.
Kaare J., Amund M., Wallin, Harriet C (1998).Determination of Magnesium and Calcium
in Foods by Atomic Absorption Spectrometry after Microwave Digestion: NMKL
Collaborative Study. Journal of AOAC international 81 (6) 1202-1208.
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(i) Copper
Copper is a transition metal with an atomic mass of 63.54. Three oxidation states of copper exist;
cuprous (Cu+), cupric (Cu2+) and Cu0 (Uauy et al, 1998). In biological systems, copper primarily exists
as Cu2+ with minute quantities of Cu+ being found in solution. (EFSA, 2003)
Golden Standard
ISO 11885: 2007 Water quality -- Determination of selected elements by inductively coupled
plasma optical emission spectrometry (ICP-OES)
ISO 17294:2003: Water quality -- Application of inductively coupled plasma mass spectrometry
(ICP-MS) -- Part 2: Determination of 62 elements
EN 14084:2003 Foodstuffs - Determination of trace elements - Determination of lead,
cadmium, zinc, copper and iron by atomic absorption spectrometry (AAS) after microwave
digestion
EN 14082:2003 Foodstuffs - Determination of trace elements - Determination of lead,
cadmium, zinc, copper, iron and chromium by atomic absorption spectrometry (AAS) after dry
ashing
i. Method Indicator
Name
Code
Scope
Determination of Copper in foodstuffs in all relevant matrix successfully tested in laboratory
proficiency testing.
Principle
Edible parts are grinder and homogenised in suitable apparatus. The organic matrix are
removed by microwave digestion or by dry ashing. The Copper content is determined by
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flame atomic absorption spectrometry-procedures( AAS) or by Inductively coupled plasma
atomic emission spectroscopy (ICP-AES) also refered as Inductively Coupled Plasma Optical
Emission Spectrometry (ICP-OES).
Key steps
Secção 1.03
Preparation
o The edible part needs to be separate from the foodstuffs ( EN 13804:2002
provide examples of sample preparation from foodstuffs)
Homogenization
o Edible parts are grinder in suitable apparatus (coffee grinder or kitchen
grinder; stainless steel vegetable slice; plastic salad spinner and homogenised;
o To avoid contamination the apparatus equipped with titanium or ceramics
knives, agate mortar or ball mill can be used for size reduction and
homogenisation( EN 13804:2002 is the reference standard for sample
preparation
Separation
Organic matrix are removed or extracted :
o Pressure digestion: The sample dissolved in concentrated acid are digested
in a sealed vessel in a pressure container at high temperature and pressure by
conventional or microwave assisted heating. (EN 14084:2003 Foodstuffs). The
method is described for AAS and ICP OES.
o Dry Ashing : Sample in a crucible made by platinum is incinerated heating
gentling in a muffle furnace at controlled temperature 450 ºC 25 ºC. Final
residue redissolved in nitric acid .( EN 14082:2003). The method is described
for AAS.
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Detection
o The instrumental parameters for flame AAS
Flame: Air acetylene, oxidising
Wavelength 324,7 nm
o The instrumental parameters for ICP-OES
Wavelength 324,754 nm; Interferences:Cr, Fe, Mo, Ti Limit of Quantification:
(radial viewing 9 ; axial viewing 2 )
Wavelength 327,396 nm ; Co and Ti interferences; Limit of Quantification:
(radial viewing 4 ; axial viewing 3 )
Quantification
o AAS
After instrument response is stable the linearity, sensitivity and limit of
quantification verified. The content of Copper in sample is determined
from calibration curve by plotting (absorbance (A) peak area ) against
concentration. The calibration curve is prepared with at least five
points using concentrations of standard solutions within working range.
o ICP OES
After verification of instrument performance (drift; interferences,
background correction). The content of Copper in sample is
determined from linear regression method using blank, standard
solutions and , internal standards
Criteria for analytical performance and Analytical Quality
control
Method Performance
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Table 4. Relevant parameters obtained during inter laboratory studies during preparation of Golden Standards
Matrix
Standard/Matrix
Liver
paste
Apple
sauce
Minced
fish
Wheat
bran
Milk
powder
Composite
diet D/E
EN
14082
Repeatability
RSDr%
1,8
Reproducibility
RSDR (%)
4,2 *
6,0* 12* 6,9* 8,0* 3,5*
AOAC
999.11
Repeatability
RSDr%
5.3 1.8
Reproducibility
RSDR (%)
7.5 6.8 6.8 8.0 3.5
Liver Mushroom Fish Wheat
bran
Milk
powder
Diets
AOAC
999.10
Repeatability
RSDr%
1.6 - - 3.4 4.0
Reproducibility
RSDR (%)
4.8 5.3 9.1 4.8 9.3 5.3
EN
14084
Repeatability
RSDr%
3.1
7,2
1,5
Reproducibility
RSDR (%)
3,8
5,7
28
10
27
3,0
Certified Reference Materials/Standard Reference Material
Table 5. List of CRM/SRM available in 2008
NIST 2381 Baking Chocolate (reference value)
LGC 7112 Pig liver paste
NIST 2387 Peanut butter
GBW 08552 Freeze Dried Pork Muscle
NIST 1546 Meat Homogenate
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NIST 8415 Whole Egg Powder(reference value)
BCR 189 Wholemeal flour
BCR 679 Freeze dried Whole Cabbage
GBW07605 Tea
NIST 1567a Wheat Flour
NIST 1568 a Rice Flour
NIST 2383 Baby Food (reference value)
NIST 8432 Corn Starch (reference value)
NIST 8433 Com Bran (reference value)
NIST 8436 Durum Wheat Flour (reference value
VMA195
Cereal
NIST 1548a
Freeze Dried Mixed Diet
NIST 8435 Whole Milk Powder (reference value)
NIST 1846 Infant Formula (reference value)
ERMCE 278 Freeze Dried Muscle Tissue
NRCDORM2 Freeze Dried Dogfish Muscle
NIST 1549 Non –Fat Milk Powder
NIST 1566b Freeze-Dried Oyster Tissue
NIST 1570b Freeze dried Spinach Leaves
NIST 1946 Fish Tissue (reference value)
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BCR 422
Freeze – dried cod muscle
LGC 7160 Crab Paste
NIST 1577b Freeze –Dried Bovine liver
NIST 3244 Protein Powder
NRCDOLT3 Freeze Dried Dogfish liver
Proficiency Testing Schemes (www.eptis.bam.de)
o 21 datasets are register at eptis and the following matrix
Wine, Sewage sludge, vegetable oil, fat vegetable, fish oil (GFAAS),
diet food, babby food, fat animal, frying oil, Groundnut oil, Colza oil,
wheat, milk powder, flour, Mushrooms, plants, tuna fish,
Other methods available
Colorimetric
AOAC 984.27- Calcium, Copper, Iron, Magnesium, Manganese, Phosphorus,
Potassium, Sodium, and Zinc in Infant Formula- Inductively Coupled Plasma Emission
Spectroscopic Method
NMKL- AOAC 999.10 -Lead, Cadmium, Zinc, Copper, and Iron in Foods – Atomic
Absorption Spectrophotometry after microwave digestion
NMKL-AOAC 999.11- Lead, Cadmium, Zinc, Copper, and Iron in Foods – Atomic
Absorption Spectrophotometry after dry ashing
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Table 6. Recommended methods of analysis CodexStan 234-1999)-
Matrix
Method Reference Principle Type
Chocolate AOAC 960.40 (Codex general
method)
Colorimetry
(diethyldithiocarbamate)
II
Cocoa (cacao) nib,
cocoa (cacao)
mass, cocoa press
cake and cocoa dust
(cocoa fines), for use
in the
manufacturing of
cocoa and chocolate
products
AOAC 971.20 (Codex general
method)
Atomic absorption
spectrophotometry
II
Cocoa butter
confectionery
AOAC 971.20 (Codex general
method)
Atomic absorption
spectrophotometry
II
Cocoa butters AOAC 990.05
ISO 8294:1994
IUPAC 2.631
(Codex general method)
Atomic absorption
spectrophotometry
(direct graphite furnace)
II
Cocoa butters AOAC 960.40 (Codex general
method)
Colorimetry
(diethyldithiocarbamate)
III
Cocoa powders
(cocoa) and dry
cocoasugar
mixtures
AOAC 960.40 (Codex general
method)
Colorimetry
(diethyldithiocarbamate)
II
Edible casein products AOAC 985.35 Atomic absorption
spectrophotometry
II
Edible casein products IDF Standard 76A:1980
ISO 5738:1980 (confirmed
1995)
AOAC 960.40 (Codex general
method)
Colorimetry
(diethyldiethiocarbamate)
III
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Fats and oils AOAC 990.05
ISO 8294:1994
IUPAC 2.631
(Codex general method)
Atomic absorption
Spectrophotometry (direct
graphite
furnace
II
Copper Food grade
salt
ESPA/CN-E/101-1994 Photometry II
Fruit juices AOAC 971.20(Codex general
method)
Atomic absorption
spectrophotometry
II
Honey AOAC 971.20 (Codex general
method)
Atomic absorption
spectrophotometry
II
Natural mineral waters ISO 8288:1986 (confirmed
1995)
Flame atomic absorption
spectrophotometry
II
Natural mineral waters AOAC 960.40 (Codex general
method)
Colorimetry III
Vinegar AOAC 971.20(Codex general
method)
Atomic absorption
spectrophotometry
II
Whey powders AOAC 985.35 Atomic absorption
spectrophotometry
II
Whey powders IDF Standard 76A:1980
ISO 5738:1980 (confirmed
1995)
AOAC 960.40 (Codex general
method)
Photometry
(diethyldiethiocarbamate)
III
Remarks
Compatibility of data
o All methods give comparable results
o In certification campaign for BCR 063r the following methods were used for
final determination
Direct current plasma atomic emission spectrometry
Differential pulse anodic stripping voltammetry
Electrothermal atomic absorption spectrometry
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Inductively coupled plasma atomic emission spectrometry (ICP-OES)
Inductively coupled plasma mass- spectrometry (ICP-MS)
Isotope dilution mass spectrometry
Neutron activation analysis
Spectrophotometry
References
Deharveng G., Charrondière UR, Slimani N., Southgate DAT., Riboli E. (1999)
Comparison of nutrients in food composition tables available in the nine European
countries participating in EPIC. European Journal of Clinical Nutrition 53, 60-79
Cubbada, F., (2004). Inductively Coupled Plasma-Mass Spectrometry for the
determination of Elements and Elemental Species in Food: a review.J. AOAC
International, 87: 173-204
www.irmm.jrc.be/reference_materials_catalogue/BCR-063r
Greenfield H, Southgate DAT (2002) Food Composition Data – Production,
Management and Use. Elsevier Applied Science, London, UK
Jorhem, L. (2000). Determination of Metals in Foods by Atomic Absorption
Spectrometry after Dry Ashing: NMKL Collaborative Study. Journal of AOAC
INTERNATIONAL , 83 (5), 1204-1211
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Iodine
Iodine is a reactive Periodic Group VII element (halogen) existing in the valency states -1 to +7
but not occurring free in nature
Golden Standard
EN 15111:2007 Foodstuffs - Determination of trace elements - Determination of iodine by ICP-
MS (inductively coupled plasma mass spectrometry)
(i) Method Indicator
Name
Code
Scope
Extraction method for the determination of iodine compounds in foodstuffs by inductively
coupled plasma mass spectrometry (ICP-MS).
Principle
Iodine compounds are extracted with a strong alkaline reagent at elevated temperature. After
removing un-dissolved components, the nebulized solution is atomized and ionized in an
inductively coupled argon plasma. The ions are extracted from the plasma by a system of
sampler and skimmer cones, separated in a mass spectrometer on the basis of their
mass/charge ratio and determined using a pulse counting detector system
Key steps
Extraction
o Iodine compounds are extracted using tetramethylammonium hydroxide in
a dry oven at (90 ± 3) ºC
Separation for matrix
o Filtration or centrifugation
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Identification
L
o Iodine shall be evaluated at a mass of 127. The masses 125, 126 or 128 can be
used to evaluate the internal standard tellurium.
Quantification
o Determine the sample content against a calibration curve prepared with iodine
calibration solutions. The slope of calibration graph should be checked after
regular intervals (ex: 10 samples)
Criteria for analytical performance and Analytical Quality
control
Method Performance
Table 7. Relevant parameters of inter laboratory studies during preparation of ISO standard
Matrix
Parameter
Pig
Kidney
Ready-to-
serve
milk
pudding
Soy
product
Cod
Muscle
Iodised
Salt
Marine
Algae
Limit of
Quantification
(LOQ)
0,5 µg/l
RSDr (%) 7.6 7,8 3.7 0.7 6.4 0.9
RSDR (%) 19 13 6.7 8.9 15 6.2
Certified Reference Materials/Standard Reference Material
o BCR 63R SKIM Milk powder (ICP _MS)
o BCR 150 spiked skim milk powder
o BCR 151 Spiked skim milk powder
Proficiency Testing Schemes (www.eptis.bam.de)
o 3 datasets are register at eptis and the following matrix
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Diet Food ; Premix; Iodized salt
Other methods available
Catalytic measurements
Gas Chromatography
Isotope dilution mas spectrometry
Voltammetric techniques
X-Ray Fluorescence spectrometry
Dry ashing followed by titration
AOAC 992.22 Iodine (as Iodide) in Pasteurized Liquid Milk and skim milk powder (
GLChomatography)
Table 8. Recommended methods of analysis CodexStan 234-1999
Matrix
Method Reference Principle Type
Food grade salt ESPA/CN-E/109-1994 Titrimetry using sodium
thiosulphate
II
Food grade salt AOAC 925.56 Titrimetry using sodium
thiosulphate
III
Foods with low-
sodium content
(including salt
substitutes)
AOAC 925.56 Titrimetry II
(milk based formula)
Infant formula and
follow-up formula
AOAC 992.24 Ion-selective potentiometry II
Remarks
ICP-MS :This procedure requires an adequate amount of experience in operating and
optimizing the apparatus.
This limit of determination is strongly influenced by the purity of TMAH (tetramethylammonium
hydroxide) and the stability of the blank signal during measurement
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Compatibility of data
o Interlaboratories studies using spectrometric determination after digestion [2], ICP-
MS analysis after combustion in oxygen [3], or after digestion with nitric acid /
perchloricacid) performed in parallel by three laboratories revealed no significant
difference from the extraction method using dry oven at 90 ºC followed ICP-MS
determination
o In certification exercise for BCR 151 a large range of preatment techniques are
used and the following methods for final determination:
o Catalytic measurements
o Gas Chromatography
o Isotope dilution mas spectrometry
o Voltammetric techniques
o X-Ray Fluorescence spectrometry
o
References
Deharveng G., Charrondière UR, Slimani N., Southgate DAT., Riboli E. (1999)
Comparison of nutrients in food composition tables available in the nine European
countries participating in EPIC. European Journal of Clinical Nutrition 53, 60-79
Cubbada, F., 2004. Inductively Coupled Plasma-Mass Spectrometry for the
determination of Elements and Elemental Species in Food: a review.J. AOAC
International, 87: 173-204
Greenfield H, Southgate DAT (2002) Food Composition Data – Production,
Management and Use. Elsevier Applied Science, London, UK
www.irmm.jrc.be/reference materials_Catalogue_BCR-151
EuroFIR assistance to this method/guidelines
EuroFIR guidelines for assessment of Methods of Analysis
_________________________________________________________________________________
Methods of analysis
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(ii) Iron
Iron is a metal with an atomic mass of 55.8. It is present in biological systems in one of two oxidation
states, and redox interconversions of the ferrous (Fe2+) and ferric (Fe3+) forms are central to the
biological properties of this mineral. Iron is an essential constituent of oxygen carriers, such as
haemoglobin and myoglobin, and the iron contained within haem is essential for the redox reactions
of numerous cytochromes.(EFSA, 2003)
Golden Standard
ISO 11885: 2007 Water quality -- Determination of selected elements by inductively coupled
plasma optical emission spectrometry (ICP-OES)
ISO 17294:2003: Water quality -- Application of inductively coupled plasma mass spectrometry
(ICP-MS) -- Part 2: Determination of 62 elements
EN 14084:2003 Foodstuffs - Determination of trace elements - Determination of lead,
cadmium, zinc, copper and iron by atomic absorption spectrometry (AAS) after microwave
digestion
EN 14082:2003 Foodstuffs - Determination of trace elements - Determination of lead,
cadmium, zinc, copper, iron and chromium by atomic absorption spectrometry (AAS) after dry
ashing
(iii) Method Indicator
Name
Scope
Scope
Determination of Iron in foodstuffs in all relevant matrix successfully tested in laboratory
proficiency testing.
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Methods of analysis
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Principle
Edible parts are grinder and homogenised in suitable apparatus. The organic matrix are
removed by microwave digestion or by dry ashing. The Iron content is determined by flame
atomic absorption spectrometry-procedures( AAS) or by Inductively coupled plasma atomic
emission spectroscopy (ICP-AES) also refered as Inductively Coupled Plasma Optical
Emission Spectrometry (ICP-OES).
Key steps
Preparation
o The edible part needs to be separate from the foodstuffs ( EN 13804:2002
provide examples of sample preparation from foodstuffs)
Homogenization
o Edible parts are grinder in suitable apparatus (coffee grinder or kitchen
grinder; stainless steel vegetable slice; plastic salad spinner and homogenised;
o To avoid contamination the apparatus equipped with titanium or ceramics
knives, agate mortar or ball mill can be used for size reduction and
homogenisation( EN 13804:2002 is the reference standard for sample
preparation)
Separation from Matrix
Organic matrix are removed or extracted :
o Pressure digestion: The sample dissolved in concentrated acid are digested
in a sealed vessel in a pressure container at high temperature and pressure by
conventional or microwave assisted heating. (EN 14084:2003 Foodstuffs). The
method is described for AAS and ICP OES.
o Dry Ashing : Sample in a crucible made by platinum is incinerated heating
gentling in a muffle furnace at controlled temperature 450 ºC 25 ºC. Final
residue redissolved in nitric acid .( EN 14082:2003). The method is described
for AAS.
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Methods of analysis
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Detection
o The instrumental parameters for flame AAS
Flame: Air acetylene, oxidising
Wavelength 248,3 nm
o The instrumental parameters for ICP-OES
Wavelength 271,441 nm; Interferences: none Limit of Quantification: (axial
viewing non ; radial viewing non )
Wavelength 259,940 nm ; Co interferences; Limit of Quantification: (axial
viewing 2 ; radial viewing 6)
Wavelength 238,204 nm, Co, interferences ; Limit of Quantification: :
(axial viewing 3 ; radial viewing 14)
Quantification
o AAS
After instrument response is stable the linearity, sensitivity and limit of
quantification verified. The content of Iron in sample is determined
from calibration curve by plotting (absorbance (A) peak area ) against
concentration. The calibration curve is prepared with at least five
points using concentrations of standard solutions within working range.
o ICP OES
After verification of instrument performance (drift; interferences,
background correction). The content of Iron in sample is determined
from linear regression method using blank, standard solutions and ,
internal standards.
Criteria for analytical performance and Analytical
Quality control
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Methods of analysis
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Method Performance
Table 9. Relevant parameters obtained by inter laboratory studies (blank spaces results were not satisfactory)
Matrix
Standard/Matrix
Liver
paste
Apple
sauce
Minced
fish
Wheat
bran
Milk
powder
Composite
diet D/E
EN
14082
Repeatability
RSDr%
1,8
Reproducibility
RSDR (%)
4,2 *
6,0* 12* 6,9* 8,0* 3,5*
AOAC
999.11
Repeatability
RSDr%
5.3 1.8
Reproducibility
RSDR (%)
7.5 6.8 6.8 8.0 3.5
Liver Mushroom Fish Wheat
bran
Milk
powder
Diets
AOAC
999.10
Repeatability
RSDr%
1.6 - - 3.4 4.0
Reproducibility
RSDR (%)
4.8 5.3 9.1 4.8 9.3 5.3
EN
14084
Repeatability
RSDr%
5.6
4,2 4,0
Reproducibility
RSDR (%)
6,7 8,2
18 8,6
5,7
Certified Reference Materials/Standard Reference Material
Table 10. List of Reference Materials available in 2008
NIST 2384 Baking chocolate
NIST2387 Peanut Butter
GBW 08552 Freeze Dried Pork Muscle
NIST 1546 Meat Homogenate
NIST 8415 Whole Egg Powder (reference value)
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BCR 189 Wholemeal flour
BCR 679 Freeze-Dried White Cabbage
GBW 07605 Tea
NIST 1567a Wheat flour
NIST 1568a Rice Flour
NIST 2383 Baby Food (reference value)
NIST 8433 Corn Bran (reference value)
NIST 8436 Durum Wheat Flour (reference value)
VMA 195 Cereal
NIST 1548a Freeze dried mixed diet
NIST 1846 Infant Formula
NIST 8435 Whole milk powder
NRDCDORM 2 Freeze-Dried DogFish Muscle
NIST 1549 Non-Fat Milk Powder
NIST 1566b Freeze –Dried Oyster Tissue
NIST 1946 Fish Tissue
BCR 422 Freeze dried Cod Muscle
NIST 1577b Freeze dried bovine liver
NIST 8418 wheat gluten
NRCDOLT3 Freeze dried dog fish liver
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Methods of analysis
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Proficiency Testing Schemes (www.eptis.bam.de)
o 20 datasets are register at eptis and the following matrix
water, vegetable oil, fat vegetable, fish oil, wine, liqueurs, cognac, diet
food, baby food, olive oil, plants, meat, tuna fish, cheese processed,
meat products, dietary supplements
Other methods available
AOAC 984.27- Calcium, Copper, Iron, Magnesium, Manganese, Phosphorus,
Potassium, Sodium, and Zinc in Infant Formula- Inductively Coupled Plasma Emission
Spectroscopic Method
NMKL- AOAC 999.10 -Lead, Cadmium, Zinc, Copper, and Iron in Foods – Atomic
Absorption Spectrophotometry after microwave digestion
NMKL-AOAC 999.11- Lead, Cadmium, Zinc, Copper, and Iron in Foods – Atomic
Absorption Spectrophotometry after dry ashing
Table 11. CodexStan 234-1999)-Recommended methods of analysis
Matrix
Method Reference Principle Type
Cocoa butters AOAC 990.05
ISO 8294:1994
IUPAC 2.631
(Codex general method)
Atomic absorption
spectrophotometry(direct
graphite furnace)
II
Cocoa butters BS 684 Section 2.17:1976 Colorimetry III
Fats and oils AOAC 990.05
ISO 8294:1994
IUPAC 2.631
(Codex general method)
Atomic absorption
spectrophotometry
(direct graphite furnace)
II
Fruit juices IFJU Method No 15, 1964 Photometry II
Milk products NMKL 139 (1991) (Codex
general method
Atomic absorption
spectrophotometry
II
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Methods of analysis
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Milk products IDF Standard 103A:1986
ISO 6732:1985 (confirmed
1995)
Photometry
(bathophenanthroline)
IV
Vinegar IFJU Method No 15, 1964 Photometry IV
dissolved in Natural
mineral waters
ISO 6332:1988 (confirmed
1995)
Spectrophotometry II
Remarks
Old Data
o Colorimetric methods are available and described in same tables
Compatibility of old data
o According with (Deharveng, 1999) methods give similar results. Contamination
with dust resulting in a high variability
References
Deharveng G., Charrondière UR, Slimani N., Southgate DAT., Riboli E. (1999)
Comparison of nutrients in food composition tables available in the nine European
countries participating in EPIC. European Journal of Clinical Nutrition 53, 60-79
Cubbada, F., 2004. Inductively Coupled Plasma-Mass Spectrometry for the
determination of Elements and Elemental Species in Food: a review.J. AOAC
International, 87: 173-204
Jorhem, L. (2000). Determination of Metals in Foods by Atomic Absorption
Spectrometry after Dry Ashing: NMKL Collaborative Study. Journal of AOAC
INTERNATIONAL , 83 (5), 1204-1211
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(iv) Magnesium
(v)
Magnesium (Mg) belongs to group II of the third period of the Periodic Table of Elements, a
group that includes two other physiologically important elements: calcium and zinc. Mg has an
atomic weight of 24.312; its atomic number is 12; its valency 2.
Golden Standard
ISO 11885: 2007 Water quality -- Determination of selected elements by inductively coupled
plasma optical emission spectrometry (ICP-OES)
ISO 17294:2003: Water quality -- Application of inductively coupled plasma mass spectrometry
(ICP-MS) -- Part 2: Determination of 62 elements
prEN 15505 Foodstuffs - Determination of trace elements - Determination of sodium,
magnesium and calcium by flame atomic absorption spectrometry (AAS) after microwave
digestion
Method Indicator
Name
Code
Scope
Determination of Magnesium in foodstuffs in all relevant matrix successfully tested in
laboratory proficiency testing.
Principle
Edible parts are grinder and homogenised in suitable apparatus. The organic matrix are
removed by microwave digestion. The Magnesium content is determined by flame atomic
absorption spectrometry-procedures( AAS) or by Inductively coupled plasma atomic emission
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spectroscopy (ICP-AES) also refered as Inductively Coupled Plasma Optical Emission
Spectrometry (ICP-OES).
Key steps
Secção 1.04
Preparation
o The edible part needs to be separate from the foodstuffs ( EN 13804:2002
provide examples of sample preparation from foodstuffs)
Homogenization
o Edible parts are grinder in suitable apparatus (coffee grinder or kitchen
grinder; stainless steel vegetable slice; plastic salad spinner and homogenised;
o To avoid contamination the apparatus equipped with titanium or ceramics
knives, agate mortar or ball mill can be used for size reduction and
homogenisation( EN 13804:2002) is the reference standard for sample
preparation
Separation
Organic matrix are removed or extracted :
o Pressure digestion: The sample dissolved in concentrated acid are digested
in a sealed vessel in a pressure container at high temperature and pressure by
conventional or microwave assisted heating. (EN 13805). The method is
described for AAS and ICP OES.
Detection
o The instrumental parameters for flame AAS
Flame: Air acetylene, oxidising
Wavelength 285.5 nm
o The instrumental parameters for ICP-OES
Wavelength 279,078 nm; Interferences: Fe ;Limit of Quantification: (radial
viewing 33 ; axial viewing 19 )
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Wavelength 279,553 nm; Interferences: Fe ;Limit of Quantification: (radial
viewing 1; axial viewing 7
Wavelength 285,213 nm ; Cr interferences; Limit of Quantification: (radial
viewing 4 ; axial viewing 14)
Quantification
o AAS
After instrument response is stable the linearity, sensitivity and limit of
quantification verified. The content of Magnesium in sample is
determined from calibration curve by plotting (absorbance (A) peak
area ) against concentration. The calibration curve is prepared with at
least five points using concentrations of standard solutions within
working range.
o ICP OES
After verification of instrument performance (drift; interferences,
background correction). The content of Magnesium in sample is
determined from linear regression method using blank, standard
solutions and , internal standards
Criteria for analytical performance and Analytical Quality control
Method Performance
Table 12. Relevant parameters obtained by EN 15505 inter laboratory studies
Matrix
Parameter
Simulated
Diet(D)
Simulated
Diet(F)
Milk
Powder
Flash
muscle
Apple Choolate
cake
Mean values
mg/kg
665 618 859 749 251 284
RSDr (%) 3.8 4.4 2.1 2.4 2.1 2.0
RSDR (%) 6.9 6.9 4.6 6.8 4.5 4.0
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Methods of analysis
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Certified Reference Materials/Standard Reference Material
Table 13. List of CRM/SRM available in 2008
LGC 7104 Sterilized cream
NIST 2384 Baking chocolate(reference value)
LGC 7112 Pig liver Paste
NIST 2387 Peanut Butter
GBW 08552 Freeze dried Pork Muscle
NIST 1546 Meat Homogenate(reference value)
NIST 8415 Whole Egg Powder(reference value)
BCR 381 Rye Flour
GBW 07605 Tea
NIST 1567a wheat Flour
NIST 1568a Rice Flour
NIST 2383 Baby Food(reference value)
NIST 8432 Corn Starch (reference value)
NIST 8433 Corn Barn(reference value)
NIST 8436 Durum Wheat Flour(reference value)
VMA 195 Cereal
VMA 399 Cereal
LGC 7105 Rice Pudding
NIST 1548a Freeze Dried Mixed Diet
NIST 1846 Infant Formula(reference value)
NIST 8435 Whole Milk Powder(reference value)
NIST 1549 Non- Fat Milk Powder
NIST 1566b Freeze Dried Oyster Tissue
NIST 2385 Slurried Spinach
NIST 1946 Fish Tissue(reference value)
LGC 7160 Crabe Paste
NIST 1577b Freeze Dried Bovine liver
NIST 3244 Protein Powder
NIST 8418 wheat gluten (reference value)
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Methods of analysis
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Proficiency Testing Schemes (www.eptis.bam.de)
o 17 datasets are register at eptis and the following matrix:
Wine, dietary supplements, diet food, baby food, fruit juice, plants,
cheese processed, meat products,
Other methods available
Table 14. Codex Recommended methods of analysis
Matrix
Method Reference Principle Type
Natural mineral waters ISO 6059:1984 (confirmed
1995)
Titrimetry II
Natural mineral waters ISO 7980:1986(confirmed
1995)
Atomic absorption
spectrophotometry
III
NMKL no 147 (2003). Magnesium and calcium; determination in foodstuffs using flame
atomic absorption spectrometry after microwave oven digestion.
Remarks
Old Data
o Colorimetry is described.
Compatibility of old data
o Methods for magnesium are compatible (Deharveng,1999)
References
Deharveng G., Charrondière UR, Slimani N., Southgate DAT., Riboli E. (1999)
Comparison of nutrients in food composition tables available in the nine European
countries participating in EPIC. European Journal of Clinical Nutrition 53, 60-79
Cubbada, F., 2004. Inductively Coupled Plasma-Mass Spectrometry for the
determination of Elements and Elemental Species in Food: a review.J. AOAC
International, 87: 173-204
EuroFIR guidelines for assessment of Methods of Analysis
_________________________________________________________________________________
Methods of analysis
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Greenfield H, Southgate DAT (2002) Food Composition Data – Production,
Management and Use. Elsevier Applied Science, London, UK
- Determination of several elements in
duplicate meals from catering establishments using closed vessel microwave digestion
with inductively coupled plasma mass spectrometry detection: Estimation of daily
dietary intake Food Additives and Contaminants 20 (1), 44-56.
Julshamn, K., Maage, A., Wallin, H.C., Lierhagen, S., Nielsen, J., A sbø, E., Engman, J.,
(...), Niemi, E.(1998). Determination of Magnesium and Calcium in Foods by Atomic
Absorption Spectrometry after Microwave Digestion: NMKL. Journal of AOAC
International 81 (6), 1202-1208
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(i) Phosphorus
Phosphorus is an element of group 5 of the periodic table and has an atomic weight of 30.97.
It is one of the most abundant elements on earth, most commonly found as the phosphate ion
(PO43-), with phosphorus in its pentavalent form.
Golden Standard
ISO 11885: 2007 Water quality -- Determination of selected elements by inductively coupled
plasma optical emission spectrometry (ICP-OES)
ISO 17294:2003: Water quality -- Application of inductively coupled plasma mass spectrometry
(ICP-MS) -- Part 2: Determination of 62 elements
ISO 9874:2006 Milk -- Determination of total phosphorus content -- Method using molecular
absorption spectrometry
AOAC - 984.27 Calcium, Copper, Iron, Magnesium, Manganese, Phosphorus, Potassium,
Sodium, and Zinc in Infant Formula- Inductively Coupled Plasma Emission Spectroscopic
Method
Scope
Determination of Phosphorus in foodstuffs in all relevant matrix successfully tested in
laboratory proficiency testing
Principle
Edible parts are grinder and homogenised in suitable apparatus. The organic matrix are
removed by microwave digestion or by dry ashing. The total Phosporus content is determined
by Spectrophotometric method or by Inductively coupled plasma atomic emission spectroscopy
(ICP-AES) also refered as Inductively Coupled Plasma Optical Emission Spectrometry (ICP-
OES).
Key steps
Preparation
o The edible part needs to be separate from the foodstuffs ( EN 13804:2002
provide examples of sample preparation from foodstuffs)
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Homogenization
o Edible parts are grinder in suitable apparatus (coffee grinder or kitchen
grinder; stainless steel vegetable slice; plastic salad spinner and homogenised;
o To avoid contamination the apparatus equipped with titanium or ceramics
knives, agate mortar or ball mill can be used for size reduction and
homogenisation( EN 13804:2002 is the reference standard for sample
preparation)
Separation from Matrix
Organic matrix are removed or extracted :
o Pressure digestion: The sample dissolved in concentrated acid are digested
in a sealed vessel in a pressure container at high temperature and pressure by
conventional or microwave assisted heating. (EN 14084:2003 Foodstuffs). The
method is described for ICP OES.
o Ashing :. Foodstuffs are heated at 470ºC in an oven during 24-48h and reduced to ashes
(organic ingredients and water were removed and carbon is not present). Ashes are treated
with conc. HCl and taken to dryness in a water bath. The solid residue is dissolved with 10%
HNO3 acid and boiled in a water bath during 5 min, avoiding the orthophosphates hydrolysis
that produce coloured solutions. After cooling to room temperature, ashes are transferred to
a volumetric flash and diluted with water (1:2).
Detection
o Phosphorus content is determined by Spectrophotometric method UV-Vis
double-beam at 430nm
o The instrumental parameters for ICP-OES
Wavelength 177,434 nm; Interferences: Cu Limit of Quantification: (radial
viewing 9 ; axial viewing 2 )
Wavelength 213,618 nm ; Co,Cu,Fe,Mo,Zn interferences; Limit of
Quantification: (radial viewing 4 ; axial viewing 3 )
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Quantification.
After instrument response is stable the linearity, sensitivity and limit of
quantification verified. The content of phosphorous in sample is
determined from calibration curve by plotting (absorbance (A) peak
area ) against concentration. The calibration curve is prepared with at
least five points using concentrations of standard solutions within
working range.
Criteria for analytical performance and Analytical
Quality control
Method Performance
Table 15. Relevant parameters obtained during inter laboratory studies
AOAC 986.24
Infant Formula
Spectrophotometric
method
Parameter Enteral RTF
soy
RTF
soy
Soy
powder
Whey
powder
Mean
Parameter
541 526 447 3908 2350
RSDr% 3.0 2.4
RSDR% 3.5 3.7 11 3.4 31
Certified Reference Materials/Standard Reference Material
Table 16. List of CRM/SRM available in 2008
LGC 7104- Sterilized cream
NIST 2381 Baking chocolate
LGC 7112 Pig liver Paste
NIST 2387 Peanut Butter
GBW 08552 Freeze dried Pork Muscle
NIST 1546 Meat Homogenate (reference value)
NIST 8415 Whole Egg Powder(reference value)
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_________________________________________________________________________________
Methods of analysis
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GBW 07605 Tea
LGC 7103 Sweet digestive Biscuit
NIST 1567a wheat Flour
NIST 1568a Rice Flour
NIST 2383 Baby Food
NIST 8432 Corn Starch (reference value )
NIST 8433 Corn Barn (reference value )
NIST 8436 Durum Wheat Flour(reference value )
VMA 195 Cereal
VMA 399 Cereal
LGC 7105 Rice Pudding
NIST 1548a Freeze Dried Mixed Diet
NIST 1846 Infant Formula (reference value
NIST 8435 Whole Milk Powder(reference value )
NIST 1549 Non- Fat Milk Powder
NIST 1570a Freeze Dried Spinach Leaves
NIST 2385 Slurried Spinach
NIST 1946 Fish Tissue (reference value )
BCR 487 value ) Freeze Dried Pigs Liver(reference
LGC 7160 Crabe Paste
NIST 1577b Freeze Dried Bovine liver
NIST 3244 Protein Powder
NIST 8418 wheat gluten (reference value )
Proficiency Testing Schemes (www.eptis.bam.de)
o 20 datasets are register at eptis and the following matrix
o Canned meat, Sewage sludge, vegetable oil (GFAAS), fat vegetable,
(GFAAS), diet food, baby food, fat animal, fish oil, frying oil, Groundnut oil,
diet food, meat products, olive oil, fish oil, frying oil, groundnut oil, colza oil,
milk evaporated, cheese processed, oil, dietary supplements, evaporated
milk
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Other methods available
-
Table 17. Recommended methods of analysis CodexStan 234-1999
Matrix
Method Reference Principle Type
Special foods AOAC 986.24 Colorimetry
(molybdovanadate)
II
Processed cheese
products
IDF Standard 33C: 1987
ISO 2962:1984 (confirmed
1994)
AOAC 990.24
Spectrophotometry
(molybdateascorbic
acid)
II
ISO standards
ISO 10540-1:2003 Animal and vegetable fats and oils -- Determination of phosphorus
content -- Part 1: Colorimetric method
ISO 10540-2:2003 Animal and vegetable fats and oils -- Determination of phosphorus
content -- Part 2: Method using graphite furnace atomic absorption spectrometry
ISO 9874:2006 Milk -- Determination of total phosphorus content -- Method using molecular
absorption spectrometry
ISO 2294:1974 Meat and meat products -- Determination of total phosphorus content
ISO 10540-3:2002 Animal and vegetable fats and oils -- Determination of phosphorus
content -- Part 3: Method using inductively coupled plasma (ICP) optical emission
spectroscopy
ISO 3946:1982 Starches and derived products -- Determination of total phosphorus content
-- Spectrophotometric method
ISO 2962:1984 Cheese and processed cheese products -- Determination of total
phosphorus content -- Molecular absorption spectrometric method
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Methods of analysis
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AOAC 986.24- Phosphorus in Infant Formula and Enteral Products Spectrophotometric
Method
Remarks
Compatibility of old data
o Values in tables are compatible according with results reported by Southgate
o Recently Results of FAPAS have demonstrated total Phosphorous determined
buy ICP-OES or and spectrometric method agree
References
Deharveng G., Charrondière UR, Slimani N., Southgate DAT., Riboli E. (1999)
Comparison of nutrients in food composition tables available in the nine European
countries participating in EPIC. European Journal of Clinical Nutrition 53, 60-79
Greenfield H, Southgate DAT (2002) Food Composition Data – Production,
Management and Use. Elsevier Applied Science, London, UK
Pulliainen TK, Wallin HC. (1996). Determination of total phosphorus in foods by
colorimetry: summary of NMKL collaborative study. J AOAC Int. 79(6):1408-11.
Cook KK.(1997)Extension of dry ash atomic absorption and spectrophotometric
methods to determination of minerals and phosphorus in soy-based, whey-based,
and enteral formulae (modification of AOAC Official Methods 985.35 and
986.24): collaborative study. J AOAC Int. 80(4):834-44.
T. Koizumi, K. Murakami and H. Nakayama et al., (2002), Role of dietary
phosphorus in the progression of renal failure, Biochem Biophys Res Commun
295 :917–921
Catherine M. Sullivan, Janeen B. Leon and Ashwini R. Sehgal 2007
Phosphorus-Containing Food Additives and the Accuracy of Nutrient Databases:
Implications for Renal Patients Journal of Renal Nutrition, 17(5) : 350-354
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(ii) Potassium
Potassium in foods is associated with salts of weak organic acids. Various potassium salts, e.g.
KCl, are used in many applications, amongst others as ingredients in foods (e.g. additives), food
supplements and drugs, household chemicals etc. In this opinion, the term potassium refers to
ionic potassium, except where specific potassium compounds are stated. One mmol potassium
is equivalent to 39.1 mg.
Golden Standard
ISO 11885: 2007 Water quality -- Determination of selected elements by inductively coupled
plasma optical emission spectrometry (ICP-OES)
ISO 17294:2003: Water quality -- Application of inductively coupled plasma mass spectrometry
(ICP-MS) -- Part 2: Determination of 62 elements
AOAC 984.27- Calcium, Copper, Iron, Magnesium, Manganese, Phosphorus, Potassium,
Sodium, and Zinc in Infant Formula- Inductively Coupled Plasma Emission Spectroscopic
Method
AOAC 985.35- Minerals in Infant Formula Enteral Products and Pet Foods – Atomic Absorption
Spectrometric Method
(iii)
(iv) Method Indicator
Name
Code
Scope
Determination of Potassium in foodstuffs in all relevant matrix successfully tested in laboratory
proficiency testing.
Principle
Edible parts are grinder and homogenised in suitable apparatus. The organic matrix are
removed by microwave digestion or by dry ashing. The Potassium content is determined by
flame atomic absorption spectrometry-procedures( AAS) or by Inductively coupled plasma
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Methods of analysis
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atomic emission spectroscopy (ICP-AES) also refered as Inductively Coupled Plasma Optical
Emission Spectrometry (ICP-OES).
Key steps
Preparation
o The edible part needs to be separate from the foodstuffs ( EN 13804:2002
provide examples of sample preparation from foodstuffs)
Homogenization
o Edible parts are grinder in suitable apparatus (coffee grinder or kitchen
grinder; stainless steel vegetable slice; plastic salad spinner and homogenised;
o To avoid contamination the apparatus equipped with titanium or ceramics
knives, agate mortar or ball mill can be used for size reduction and
homogenisation( EN 13804:2002 is the reference standard for sample
preparation
Separation
Organic matrix are removed or extracted :
o Pressure digestion: The sample dissolved in concentrated acid are digested
in a sealed vessel in a pressure container at high temperature and pressure by
conventional or microwave assisted heating. (EN 14084:2003 Foodstuffs). The
method is described for AAS and ICP OES.
o Dry Ashing : Sample in a crucible made by platinum is incinerated heating
gentling in a muffle furnace at controlled temperature 450 ºC 25 ºC. Final
residue redissolved in nitric acid .( EN 14082:2003). The method is described
for AAS.
Detection
o The instrumental parameters for flame AAS
Flame: Air acetylene, oxidising
Wavelength 766.5 nm
o The instrumental parameters for ICP-OES
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Methods of analysis
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Wavelength 766,490 nm; Interferences: Ar, Ba, Mg Limit of Quantification:
(radial viewing 66 ; axial viewing 20 )
Wavelength 769,896 nm ; Ba interferences; Limit of Quantification: (radial
viewing - ; axial viewing (230) )
Quantification
o AAS
After instrument response is stable the linearity, sensitivity and limit of
quantification verified. The content of Potassium in sample is
determined from calibration curve by plotting (absorbance (A) peak
area ) against concentration. The calibration curve is prepared with at
least five points using concentrations of standard solutions within
working range.
o ICP OES
After verification of instrument performance (drift; interferences,
background correction). The content of Potassium in sample is
determined from linear regression method using blank, standard
solutions and , internal standard
Criteria for analytical performance and Analytical Quality
control
Method Performance
Table 18. Relevant parameters obtained in AOAC AAS- 985.35 inter laboratory studies
Matrix
Parameter
Enteral 7 RTF
soy2
RTF
soy(4and 6)
Soy
Powder
(1and5)
Whey
powder 3
Mean (μg/g 1340 1050 840 6390 5080
RSDr% 2.0 2.0
RSD R% 6.8 2.7 2.1 5.6 3.0
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Methods of analysis
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Certified Reference Materials/Standard Reference Material
Table 19. List of CRM/SRM available in 2008
LGC 7104 Sterilized cream
NIST 2384 Baking chocolate(reference value)
LGC 7112 Pig liver Paste
NIST 2387 Peanut Butter
GBW 08552 Freeze dried Pork Muscle
LGC 7000 Beef Pork Meat
LGC 7001 Mackerel Paste
NIST 1546 Meat Homogenate(reference value)
NIST 8415 Whole Egg Powder(reference value)
BCR 381 Rye Flour
BCR 383 Freeze Dried Green Beans
GBW 07605 Tea
LGC 7103 Sweet digestive Biscuit
NIST 1567a wheat Flour
NIST 1568a Rice Flour
NIST 2383 Baby Food(reference value)
NIST 8432 Corn Starch (reference value)
NIST 8433 Corn Barn(reference value)
NIST 8436 Durum Wheat Flour(reference value)
VMA 195 Cereal
VMA 399 Cereal
LGC 7105 Rice Pudding
NIST 1548a Freeze Dried Mixed Diet
NIST 1846 Infant Formula(reference value)
NIST 8435 Whole Milk Powder(reference value)
LGC 7001 Pork Meat
NIST 1549 Non- Fat Milk Powder
NIST 1566b Freeze Dried Oyster Tissue
NIST 1570a Freeze Dried Spinach Leaves
NIST 2385 Slurried Spinach
NIST 1946 Fish Tissue(reference value)
LGC 7160 Crabe Paste
NIST 1577b Freeze Dried Bovine liver
NIST 3244 Protein Powder
NIST 8418 wheat gluten (reference value)
EuroFIR guidelines for assessment of Methods of Analysis
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Methods of analysis
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Proficiency Testing Schemes (www.eptis.bam.de)
o 20 datasets are register at eptis and the following matrix
wine, fruit juice, water, milk powder, diet food, plants, canned meat,
cheese processed, dietary supplements,
Other methods available
Table 20. CodexStan 234-1999)-Recommended methods of analysis
Matrix
Method Reference Principle
Food grade salt ESPA/CN-E/104-1994
(applicable to products containing _2 mg-
K/kg)
Flame atomic absorption
spectrophotometry
Food grade salt ESPA/CN-E/103-1994
(applicable to products containing _100 mg-
K/kg)
Titrimetry
Special foods ISO 8070:1987(confirmed 1992)
IDF Standard 119A:1987
Flame emission
spectrophotometry
Special foods AOAC 984.27 ICP emission
spectrometry
Remarks
Old Data
o AOAC 969.23 - Flame Photometric Method Sodium and Potassium in Seafood
o IDF-ISO-AOAC 990.23 - Flame Emission Spectrometric Method- Sodium and
Potassium in Dried Milk
Compatibility of old data
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Methods of analysis
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o All methods give similar results.(Southgate, 2002)
o Flame photometry can be used with very good results demonstrated in PT
schemes although mutual interference from phosphorus can occur(Chen
2005)
References
Deharveng G., Charrondière UR, Slimani N., Southgate DAT., Riboli E. (1999)
Comparison of nutrients in food composition tables available in the nine European
countries participating in EPIC. European Journal of Clinical Nutrition 53, 60-79
Cook KK. (1997). Extension of dry ash atomic absorption and spectrophotometric
methods to determination of minerals and phosphorus in soy-based, whey-based, and
enteral formulae (modification of AOAC Official Methods 985.35 and 986.24):
collaborative study. J AOAC Int.;80(4):834-44
Greenfield H, Southgate DAT (2002) Food Composition Data – Production,
Management and Use. Elsevier Applied Science, London, UK
Dwyer JT, Holden J, Andrews K, Roseland J, Zhao C, Schweitzer A, Perry CR, Harnly
J, Wolf WR, Picciano MF, Fisher KD, Saldanha LG, Yetley EA, Betz JM, Coates PM,
Milner JA, Whitted J, Burt V, Radimer K, Wilger J, Sharpless KE, Hardy CJ. (2007).
Measuring vitamins and minerals in dietary supplements for nutrition studies in the USA
Anal Bioanal Chem.;389(1):37-46. Epub 2007 Jul 20. Review.
Haytowitz, D.B. Pehrsson P. R. and Holden JM. The National Food and Nutrient
Analysis Program: A decade of progress (2008) Journal of Food Composition and
Analysis, 21, Supplement 1, S94-S102.
Chen,M.-J. Hsieh, YT, Weng Y-M, Chiou R. Y.-Y. (2005). Flame photometric
determination of salinity in processed foods Food Chemistry, 91, (4) 765-770.
.
Secção 1.05 EuroFIR assistance to this method/guidelines
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(i) Selenium
Foods contain a number of different selenium forms. In animal foods, there are specific
selenium proteins where selenium is incorporated via selenide as selenocysteine, while
selenomethionine, and possibly also selenocysteine to some extent, are non-specifically
incorporated as analogues to methionine and cysteine in foods both of animal and plant origin.
Selenomethionine, as well as the inorganic forms selenite and selenate, are the most common
forms in food supplements and fodder additives. Although extensively used for research
purposes, it is uncertain if the inorganic forms occur in foods. In addition to these forms a
number of uncharacterised forms exist, e.g. in fish (Åkesson and Srikumar, 1994), but their
contribution to total dietary selenium is unknown.
Selenium forms used in supplements are inorganic selenite and selenate and organic selenium
in then form of selenomethionine, selenocystine and selenium enriched yeast. The forms of
selenium found in yeast vary according to production process and the selenomethionine has
been suggested to comprise 20 to 50% of the selenium and that some is bound as
selenotrisulphides (SCF, 1999).
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Fig1 Selenium Compounds and their structural formula (Dumont, 2006)
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Fig 2 Selenium Compounds and their structural formula (Dumont, 2006)
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Fig 3 Selenium Compounds and their structural formula (Dumont, 2006)
Golden Standard
EN 14627:2005 Foodstuffs - Determination of trace elements - Determination of total arsenic
and selenium by hydride generation atomic absorption spectrometry (HGAAS) after pressure
digestion
Codex-Adopted-AOAC -986.15 Arsenic, Cadmium, Lead, Selenium, and Zinc in Human and Pet
Foods Spectroscopy/Atomic Absorption Spectroscopy, Anodic Stripping Voltammetry
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Scope
Determination of Total Selenium in both inorganic species (IV and VI) in foodstuffs in all
relevant matrix successfully tested in laboratory proficiency testing. The method is not
applicable for determination of organoselenium compounds
Principle
These techniques use wet-sample digestion (e.g., nitricperchloric acid) to destroy organic
matter. Sample reduction to convert Se(VI) (+6 valence state) to Se(IV) (+4 valence state) is
necessary prior to using sodium borohydride to reduce all selenium present to selenium hydride
The selenium hydride is thermally decomposed and atomized in the sample beam of the atomic
absorption spectrophotometer. Nitric-perchloric acid is commonly used for the digestion step.
Because perchloric acid is potentially explosive, use of phosphoric acid instead is also
common..
Key steps
Preparation
o The edible part needs to be separate from the foodstuffs ( EN 13804:2002
provide examples of sample preparation from foodstuffs)
Homogenization
o Edible parts are grinder in suitable apparatus (coffee grinder or kitchen
grinder; stainless steel vegetable slice; plastic salad spinner and homogenised;)
o To avoid contamination the apparatus equipped with titanium or ceramics
knives, agate mortar or ball mill can be used for size reduction and
homogenisation( EN 13804:2002 is the reference standard for sample
preparation)
Extraction
Sample decomposition was performed by the microwave digestion Samples were
prepared by digesting in microwave furnace with nitric acid and peroxide and water .
The microwave conditions are settled according with matrix type. After cooling and
filtration, each solution was made up to reference volume with water heated with
pp p t d m t f H w t th 6 ∞
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Detection
The following instrumental parameters were used:
Wavelength = 196.0 nm
SBW = 1.0 nm
Hollow Cathode Lamp Current = 10 mA
Integration Time 25 seconds
Peak Height or Peak Area
Background Correction
Recorder Fast (0.1 second response time)
Lean Air Acetylene Flam
Quantification
After instrument response is stable the linearity, sensitivity and limit of
quantification verified. The content of Selenium IV and VI in sample is
determined from calibration curve by plotting (absorbance (A) peak area )
against concentration. The calibration curve is prepared with at least five
points using concentrations of standard solutions within working range.
Criteria for analytical performance and Analytical Quality
control
Certified Reference Materials/Standard Reference Material
Table 21. List of CRM/SRM available in 2008
LGC 7112 Pig liver Paste
GBW 08552 Freeze dried Pork Muscle
NIST 8415 Whole Egg Powder(reference value)
BCR 189 Wholemeal flour
BCR 381 Rye Flour
NIST 1567a wheat Flour
NIST 1568a Rice Flour
NIST 2383 Baby Food(reference value)
NIST 8432 Corn Starch (reference value)
NIST 8433 Corn Barn(reference value)
NIST 8436 Durum Wheat Flour(reference value)
NIST 1548a Freeze Dried Mixed Diet
NIST 1846 Infant Formula(reference value)
NIST 8435 Whole Milk Powder(reference value)
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ERMCE 278 Freeze Dried Muscle Tissue
NRCDORM 2 Freeze Dried Dogfish Muscle
NIST 1549 Non- Fat Milk Powder
NIST 1566b Freeze Dried Oyster Tissue
NIST 1570a Freeze Dried Spinach Leaves
NIST 1946 Fish Tissue(reference value)
BCR 422 Freeze Dried Cod Muscle
NIST 1577b Freeze Dried Bovine liver
NIST 8418 wheat gluten (reference value)
NRCDOLT 3 Freeze Dried Dogfish Liver
Proficiency Testing Schemes (www.eptis.bam.de)
o 8 datasets are register at eptis and the following matrix
diet food, wheat, milk powder, vegetables, water, premix,
Other methods available
A variety of analytical methods can be used to determine trace concentrations (ng/g) of
selenium in biological tissues. These include fluorometry, neutron activation analysis (NAA),
atomic absorption spectroscopy (AAS), inductively coupled plasma-atomic emission
spectroscopy (ICP-AES), inductively coupled plasma-mass spectrometry (ICP-MS), gas
chromatography (GC), spectrophotometry, x-ray fluorescence analysis, and other
Table 22. CodexStan 234-1999)-Recommended methods of analysis
Matrix
Method Reference Principle Type
Natural mineral waters AOAC 986.15 Atomic absorption
spectrophotometry
II
AOAC 996.17-Selenium in Feeds and Premixes Hydride Generation Atomic Absorption
Spectroscopy
(ii) Selenium speciation
Hyphenated Techniques for Element Speciation
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Selenium attracted the greatest interest with regard speciation, the possible role of this
element in the prevention of certain forms of cancer and other diseases. According with
Cubadda essential selenium species will be listed on food composition labels.
(iii)
Selenium speciation has become a prominent topic of present research in food science to
gain information on bioavailability, essentility, or toxicity of element present in food.
HPLC-ICP-MS has gained the highest popularity for the purpose of speciation. Prior to
the introduction into plasma the different chemical species are separated from one
another using different chromatographic principles exploited size –exclusion, reverse-
phase, ion-exchange in a combination of column and mobile phase, precede by
appropriate extraction procedures (Cubadda,2004). This methodology is preceded by
extraction techniques the results obtained depended critically on the sample
preparation procedure used (Soxhelet, room temperature mixing, sonication etc). The
preservation of species identity is another problem. The unavailability of Certified
references materials and interlaboratory collaborative studies and other quality tools
are pitfalls that make difficult at present to include results from speciation into Food
composition Databanks. Although Selenium speciation is a very important topic that
need to be followed by compilers and those involved with data compilation process.
The work of Wayne Wolf in USDA should be followed with attention because is one of
the groups where research in selenium speciation is orientated to food composition
data.
Remarks total selenium
The use of hydride generation with a normal acid sodium tetrahydroborate reaction provides
exceptional sensitivity with continuous flow hydride generators. In some situations there are
interferences which will mask the sensitivity. An alternative chemistry system using alkaline
solutions is the possibility of simultaneous removal of seriously interfering elements such as
nickel and copper as the hydroxides.
In order cases when samples has Se(VI) is not reducible by tetrahydroborate and Se(IV) it
is possible to distinguish between Se(VI) and Se(IV) in such samples, because Se(IV) can
be determined separately and, after a chemical reduction of Se(VI) to Se(IV), the total
concentration of selenium (that is Se(IV) + Se(VI)) can be determined. However, if a sample
is acidified before the analysis (for instance for preservation purposes), this reaction is likely
to take place within the time of analysis, prohibiting the possibility of determining both
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oxidation forms. Standard solutions should therefore be subjected to the same reduction
process as the samples to ensure that all selenium is present as SeIV. All standard and
sample solutions should be cooled to room temperature before analysis
For an effective release of the gaseous hydrides some parameters are of importance: the
sample acidity, the concentration and the flow of reducing agent (tetrahydroborate)
Incomplete destruction of organic matter and losses caused by volatilisation of selenium
can produced low recoveries
Latest Review
o Dumont E, Vanhaecke F, Cornelis R. 2006 Selenium speciation from food
source to metabolites: a critical review. Anal Bioanal Chem.;385(7):1304-23.
Review
On Going Research Project:
o Methods for Identification and Determination of S and Se Containing
Compounds in Foods : (2004-2009)USDA
Compatibility of data
Depends on method specificity
Commonly used instrumental methods to measure inorganic selenium include hydride
generation coupled with either atomic absorption spectrometry (HG-AAS) or with
inductively coupled plasma emission spectrometry (HG-ICPES) [5,6], graphite furnace
atomic absorption spectrometry (GFAAS) differential pulse polarography (DPP) and
cathodic stripping voltammetry .
The selenium content in fish requires a digestion method that is extremely thorough in
decomposing organic matter, and yet does not result in conditions under which
selenium is lost.
Lambert ( 2000) analysed several methods for digestion they concluded AOAC
method produced acceptable results
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References
Arnault I,Auger J. (2006) Seleno-compounds in garlic and onion. J Chromatogr.
21;1112(1-2):23-30
Dumont E, Ogra Y, Vanhaecke F, Suzuki KT, Cornelis R. Anal Bioanal Chem. 2006
Liquid chromatography-mass spectrometry (LC-MS): a powerful combination for
selenium speciation in garlic (Allium sativum). Mar;384(5):1196-206. Epub 2006 Jan 25.
Tinggi, U(1999) Determination of selenium in meat products by hydride generation
atomic absorption spectrophotometry.J-AOAC-Int. 82 (2) 364-367
Cubadda, F (2004). Inductively Coupled Plasma- Mass Spectrometry for determination
of elements and elemental species in food: A review. Journal AOAC, 87 (1) 173-204.
Pedrero Z, Elvira D, Cámara C, Madrid Y. (2007) .Selenium transformation studies
during broccoli (Brassica oleracea) growing process by liquid chromatography-
inductively coupled plasma mass spectrometry (LC-ICP-MS). Anal Chim
Acta.;596(2):251-6.
Wolf WR, Goldschmidt RJ. Updated estimates of the selenomethionine content of NIST
wheat reference materials by GC-IDMS. Analytical and Bioanalytical Chemistry.
2007;387(7):2449-52.
Yang L, Sturgeon RE, Wolf WR, Goldschmidt RJ, Mester Z. Determination of
selenomethionine in yeast using CNBr derivatization and species specific isotope
dilution GC ICP-MS and GC-MS. Journal of Analytical Atomic Spectrometry.
2004;19(11):1448-53.
Wolf WR, Goldschmidt RJ. Selenomethionine contents of NIST wheat reference
materials. Analytical and Bioanalytical Chemistry. 2004;378(5):1175-81.
EuroFIR assistance to this method/guidelines
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(iv) Sodium
Sodium (Na) is a metal with an atomic mass of 23. It is found widely in nature and as a normal
constituent of foods. It is added to foods, most frequently as sodium chloride (NaCl), common
known as salt (1 mmol is equivalent to 23 mg sodium and approximates 58 mg sodium
chloride), but also as other salts, e.g. nitrate, nitrite, phosphates, glutamate. In drinking water,
the guide level of sodium is 20 mg/L (Council Directive 80/778/EEC)
Golden Standard
prEN 15505 Foodstuffs - Determination of trace elements - Determination of sodium,
magnesium and calcium by flame atomic absorption spectrometry (AAS) after microwave
digestion
NKML 180, 2005 Sodium. Determination in Foodstuffs by Flame Atomic Absorption
Spectrometry after Microwave Digestion
AOAC 984.27 -Calcium, Copper, Iron, Magnesium, Manganese, Phosphorus, Potassium,
Sodium, and Zinc in Infant Formula- Inductively Coupled Plasma Emission Spectroscopic
Method
Method Indicator
Name
Code
Scope
Determination of Sodium in foodstuffs in all relevant matrix successfully tested in laboratory
proficiency testing.
Principle
Edible parts are grinder and homogenised in suitable apparatus. The organic matrix are
removed by microwave digestion, or dry washing. The Sodium content is determined by flame
photometry (FF),flame atomic absorption spectrometry-procedures( AAS) or by Inductively
coupled plasma atomic emission spectroscopy (ICP-AES) also refered as Inductively Coupled
Plasma Optical Emission Spectrometry (ICP-OES).
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Key steps
Preparation
o The edible part needs to be separate from the foodstuffs ( EN 13804:2002
provide examples of sample preparation from foodstuffs)
Homogenization
o Edible parts are grinder in suitable apparatus (coffee grinder or kitchen
grinder; stainless steel vegetable slice; plastic salad spinner and homogenised;
o To avoid contamination the apparatus equipped with titanium or ceramics
knives, agate mortar or ball mill can be used for size reduction and
homogenisation( EN 13804:2002 is the reference standard for sample
preparation
Separation
Organic matrix are removed or extracted :
o Pressure digestion: The sample dissolved in concentrated acid are digested
in a sealed vessel in a pressure container at high temperature and pressure by
conventional or microwave assisted heating. (EN 14084:2003 Foodstuffs). The
method is described for AAS and ICP OES.
o Dry ashing : Sample in a crucible made by platinum is incinerated heating
gentling in a muffle furnace at controlled temperature 450 ºC 25 ºC. Final
residue redissolved in nitric acid .( EN 14082:2003). The method is described
for AAS and FF
Detection
o The instrumental parameters for flame AAS
Flame: Air acetylene, oxidising
Wavelength 589.6 nm
o The instrumental parameters for ICP-OES
Wavelength 330,235 nm; Interferences: Zn Limit of Quantification: (radial
viewing 20 ; axial viewing 300 )
Wavelength 588,995 nm ; Ar, V interferences; Limit of Quantification: (radial
viewing 20 ; axial viewing 200)
Wavelength 589,592 nm ; Ba interferences; Limit of Quantification: (radial
viewing 93 ; axial viewing 20)
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Quantification
o AAS
After instrument response is stable the linearity, sensitivity and limit of
quantification verified. The content of Sodium in sample is determined
from calibration curve by plotting (absorbance (A) peak area ) against
concentration. The calibration curve is prepared with at least five
points using concentrations of standard solutions within working range.
o ICP OES
After verification of instrument performance (drift; interferences,
background correction). The content of Sodium in sample is
determined from linear regression method using blank, standard
solutions and , internal standards
Criteria for analytical performance and Analytical Quality
control
Method Performance
NMKL interlaboratory study (Julshamn K, Lea P, Norli HS, 2005)
Nine laboratories participated in an interlaboratory method performance (collaborative) study of
a method for the determination of sodium in foods by flame atomic absorption spectrometry
after wet digestion, using a microwave oven technique. The method was tested on a total of 6
foods (broccoli, carrot, bread, saithe fillet, pork, and cheese) with sodium concentrations of
1480-8260 mg/kg. The repeatability relative standard deviations (RSDr) for sodium ranged from
1.9 to 6.5%. The reproducibility relative standard deviations (RSDR) ranged from 4.2 to 6.9%.
The HorRat values ranged from 0.9 to 1.6.
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Certified Reference Materials/Standard Reference Material
Table 23. List of CRM/SRM available
LGC 7104 Sterilized cream
NIST 2384 Baking chocolate(reference value)
LGC 7112 Pig liver Paste
NIST 2387 Peanut Butter
GBW 08552 Freeze dried Pork Muscle
LGC 7000 Beef Pork Meat
LGC 7001 Mackerel Paste
NIST 1546 Meat Homogenate(reference value)
NIST 8415 Whole Egg Powder(reference value)
BCR 381 Rye Flour
BCR 383 Freeze Dried Green Beans
GBW 07605 Tea
LGC 7103 Sweet digestive Biscuit
NIST 1567a wheat Flour
NIST 1568a Rice Flour
NIST 2383 Baby Food(reference value)
NIST 8432 Corn Starch (reference value)
NIST 8433 Corn Barn(reference value)
NIST 8436 Durum Wheat Flour(reference value)
VMA 195 Cereal
VMA 399 Cereal
LGC 7105 Rice Pudding
NIST 1548a Freeze Dried Mixed Diet
NIST 1846 Infant Formula(reference value)
NIST 8435 Whole Milk Powder(reference value)
LGC 7001 Pork Meat
NIST 1549 Non- Fat Milk Powder
NIST 1566b Freeze Dried Oyster Tissue
NIST 1570a Freeze Dried Spinach Leaves
NIST 2385 Slurried Spinach
NIST 1946 Fish Tissue(reference value)
LGC 7160 Crabe Paste
NIST 1577b Freeze Dried Bovine liver
NIST 3244 Protein Powder
NIST 8418 wheat gluten (reference value)
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Proficiency Testing Schemes (www.eptis.bam.de)
o 19 datasets are register at eptis and the following matrix
wine, water, milk powder, canned meat, fruit juice, plants, premix,
cheese processed, meat products, dietary supplement
Other methods available
AOAC 984.27- Calcium, Copper, Iron, Magnesium, Manganese, Phosphorus, Potassium,
Sodium, and Zinc in Infant Formula- Inductively Coupled Plasma Emission Spectroscopic
Method
AOAC 985.35- Minerals in Infant Formula Enteral Products and Pet Foods – Atomic
Absorption Spectrometric Method
AOAC 969.23 - Flame Photometric Method Sodium and Potassium in Seafood
IDF-ISO-AOAC 990.23 - Flame Emission Spectrometric Method- Sodium and Potassium in
Dried Milk
Table 24. CodexStan Recommended methods of analysis
Component Matrix
Method Reference Principle
Sodium Special foods ISO 8070:1987(confirmed
1992) IDF Standard
119A:1987
Flame emission
spectrophotometry
Sodium Special foods AOAC 984.27 ICP emission
spectrometry
Sodium
chloride
Bouillons and consommes AOAC 971.27 (Codex
general method)
Potentiometry
Sodium
chloride
Food grade salt Described in the Standard Calculation
Sodium
chloride
Margarine AOAC 971.27 (Codex
general method)
Potentiometry
Sodium
chloride
Minarine AOAC 971.27 (Codex
general method)
Potentiometry
Sodium
chloride
Processed tomato
concentrates
AOAC 971.27(Codex
general method)
Potentiometry
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Sodium
chloride
Quick frozen blocks of fish
fillet,
minced fish flesh and
mixtures of
fillets and minced fish flesh
AOAC 971.21 (Codex
general method)
Potentiometry
Sodium
chloride
Quick frozen fish sticks (fish
fingers)
and fish portions - Breaded
or in batter
AOAC 971.27 (Codex
general method)
Potentiometry
Salt Butter IDF Standard 179:1997
AOAC 971.27 (Codex
general method)
Potentiometry
(determination of
chloride, expressed
as sodium
chloride)
Salt Processed cheese products IDF Standard 88A:1979
ISO 5943:1988 (confirmed
1996)
AOAC 983.14
Potentionmetry
(determination of
chloride, expressed
as sodium
chloride)
Salt in brine Pickled cucumbers AOAC 971.27(Codex
general method)
Potentiometry
Salt in brine Table olives AOAC 971.27(Codex
general method)
Potentiometry
Salt, added Fruit juices AOAC 971.27 (Codex
general method)
Potentiometry
Salt, added Fruit juices IFJU Method No 37, 1968 Electrochemical
titrimetry
Salt Butter IDF Standard 12B: 1988
ISO 1738:1997
AOAC 960.29
Titrimetry (Mohr:
determination of
chloride, expressed
as sodium
chloride)
Remarks
Compatibility of old data
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o All the methods give comparable results
o Flame photometry can be used with very good results demonstrated in PT
schemes although mutual interference from calcium can occur(Chen 2005)
o Overestimation of sodium concentration is reported in foods with low level of
sodium when analysis are carried out by ICP-OES
References
Deharveng G., Charrondière UR, Slimani N., Southgate DAT., Riboli E. (1999)
Comparison of nutrients in food composition tables available in the nine European
countries participating in EPIC. European Journal of Clinical Nutrition 53, 60-79
Julshamn K, Lea P, Norli HS.(2005).Determination of sodium in foods by flame atomic
absorption spectrometry after microwave digestion: NMKL interlaboratory study. J
AOAC Int. 88(4):1212-6.
Cook KK. (1997). Extension of dry ash atomic absorption and spectrophotometric
methods to determination of minerals and phosphorus in soy-based, whey-based, and
enteral formulae (modification of AOAC Official Methods 985.35 and 986.24):
collaborative study. J AOAC Int.;80(4):834-44
Chen,M.-J. Hsieh, YT, Weng Y-M, Chiou R. Y.-Y. (2005). Flame photometric
determination of salinity in processed foods Food Chemistry, 91, (4) 765-770
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(v) Zinc
Zinc has an atomic weight of 65.37 and is classified as a group IIB post-transition
metal. Zinc is also present in foods and supplements as salts of the divalent cation (Zn2+
)
Golden Standard
ISO 11885: 2007 Water quality -- Determination of selected elements by inductively coupled
plasma optical emission spectrometry (ICP-OES)
ISO 17294:2003: Water quality -- Application of inductively coupled plasma mass spectrometry
(ICP-MS) -- Part 2: Determination of 62 elements
EN 14084:2003 Foodstuffs - Determination of trace elements - Determination of lead,
cadmium, zinc, copper and iron by atomic absorption spectrometry (AAS) after microwave
digestion
EN 14082:2003 Foodstuffs - Determination of trace elements - Determination of lead,
cadmium, zinc, copper, iron and chromium by atomic absorption spectrometry (AAS) after dry
ashing
i. Method Indicator
Name
Code
Scope
Determination of Zinc in foodstuffs in all relevant matrix successfully tested in laboratory
proficiency testing.
Principle
Edible parts are grinder and homogenised in suitable apparatus. The organic matrix are
removed by microwave digestion or by dry ashing. The Zinc content is determined by flame
atomic absorption spectrometry-procedures( AAS) or by Inductively coupled plasma atomic
emission spectroscopy (ICP-AES) also refered as Inductively Coupled Plasma Optical
Emission Spectrometry (ICP-OES).
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Key steps
Preparation
o The edible part needs to be separate from the foodstuffs ( EN 13804:2002
provide examples of sample preparation from foodstuffs)
Homogenization
o Edible parts are grinder in suitable apparatus (coffee grinder or kitchen
grinder; stainless steel vegetable slice; plastic salad spinner and homogenised;
o To avoid contamination the apparatus equipped with titanium or ceramics
knives, agate mortar or ball mill can be used for size reduction and
homogenisation( EN 13804:2002 is the reference standard for sample
preparation)
Separation from Matrix
Organic matrix are removed or extracted :
o Pressure digestion: The sample dissolved in concentrated acid are digested
in a sealed vessel in a pressure container at high temperature and pressure by
conventional or microwave assisted heating. (EN 14084:2003 Foodstuffs). The
method is described for AAS and ICP OES.
o Dry Ashing : Sample in a crucible made by platinum is incinerated heating
gentling in a muffle furnace at controlled temperature 450 ºC 25 ºC. Final
residue redissolved in nitric acid .( EN 14082:2003). The method is described
for AAS.
Detection
o The instrumental parameters for flame AAS
Flame: Air acetylene, oxidising
Wavelength 213,9 nm
o The instrumental parameters for ICP-OES
Wavelength 213,857 nm; Interferences: Cu, Fe, Ni; Limit of Quantification:
(axial viewing 3,3 ; radial viewing 1)
Wavelength 206,200 nm and Cr interferences; Limit of Quantification: (axial
viewing 13 ; radial viewing 5)
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Wavelength 202,548 nm and Cr, Cu, Co,Ni interferences ; Limit of
Quantification: (radial viewing 3)
Quantification
o AAS
After instrument response is stable the linearity, sensitivity and limit of
quantification verified. The content of Zinc in sample is determined
from calibration curve by plotting (absorbance (A) peak area ) against
concentration. The calibration curve is prepared with at least five
points using concentrations of standard solutions within working range.
o ICP OES
After verification of instrument performance (drift; interferences,
background correction). The content of Zinc in sample is determined
from linear regression method using blank, standard solutions and ,
internal standards.
Criteria for analytical performance and Analytical Quality
control
Method Performance
Table 25. AAS relevant parameters obtained during inter-laboratory
Matrix
Standard/Matrix
Liver
paste
Apple
sauce
Minced
fish
Wheat
bran
Milk
powder
Composite
diet D/E
EN
14082
Repeatability
RSDr%
1,8
Reproducibility
RSDR (%)
4,2 *
6,0* 12* 6,9* 8,0* 3,5*
AOAC
999.11
Repeatability
RSDr%
5.3 1.8
Reproducibility
RSDR (%)
7.5 6.8 6.8 8.0 3.5
Liver Mushroom Fish Wheat
bran
Milk
powder
Diets
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AOAC
999.10
Repeatability
RSDr%
1.6 - - 3.4 4.0
Reproducibility
RSDR (%)
4.8 5.3 9.1 4.8 9.3 5.3
EN
14084
Repeatability
RSDr%
1,6
3,4
4,0
Reproducibility
RSDR (%)
4,8
5,3
4,8
9,3
5,3
Certified Reference Materials/Standard Reference Material
Table 26. List of available CRM/SRM in 2007
LGC 7104 Sterilized cream
NIST 2384 Baking chocolate(reference value)
LGC 7112 Pig liver Paste
NIST 2387 Peanut Butter
GBW 08552 Freeze dried Pork Muscle
LGC 7000 Beef Pork Meat
NIST 1546 Meat Homogenate(reference value)
NIST 8415 Whole Egg Powder(reference value)
BCR 189 Wholemeal flour
BCR 679 Freeze Dried White Cabbage
BCR 381 Rye Flour
GBW 07605 Tea
LGC 7103 Sweet digestive Biscuit
NIST 1567a wheat Flour
NIST 1568a Rice Flour
NIST 2383 Baby Food(reference value)
NIST 8432 Corn Starch (reference value)
NIST 8433 Corn Barn(reference value)
NIST 8436 Durum Wheat Flour(reference value)
VMA 195 Cereal
VMA 399 Cereal
LGC 7105 Rice Pudding
NIST 1548a Freeze Dried Mixed Diet
NIST 1846 Infant Formula(reference value)
EuroFIR guidelines for assessment of Methods of Analysis
_________________________________________________________________________________
Methods of analysis
69/70
NIST 8435 Whole Milk Powder(reference value)
LGC 7001 Pork Meat
ERMCE 278 Freeze Dried Muscle Tissue
NRCDORM 2 Freeze Dried Dogfish Muscle
NIST 1549 Non- Fat Milk Powder
NIST 1566b Freeze Dried Oyster Tissue
NIST 1570a Freeze Dried Spinach Leaves
NIST 1946 Fish Tissue(reference value)
BCR 422 Freeze Dried Cod Muscle
LGC 7160 Crabe Paste
NIST 1577b Freeze Dried Bovine liver
NIST 3244 Protein Powder
NIST 8418 wheat gluten (reference value)
NRCDOLT 3 Freeze Dried Dogfish Liver
Proficiency Testing Schemes (www.eptis.bam.de)
o 15 datasets are register at eptis and the following matrix
water,wine, diet food, wheat, milk powder, vegetables, tuna fish,
vegetal, dietary supplement
Other methods available
AOAC 984.27- Calcium, Copper, Iron, Magnesium, Manganese, Phosphorus,
Potassium, Sodium, and Zinc in Infant Formula- Inductively Coupled Plasma Emission
Spectroscopic Method
NMKL- AOAC 999.10 -Lead, Cadmium, Zinc, Copper, and Iron in Foods – Atomic
Absorption Spectrophotometry after microwave digestion (Zn> 4 mg/kg)
NMKL-AOAC 999.11- Lead, Cadmium, Zinc, Copper, and Iron in Foods – Atomic
Absorption Spectrophotometry after dry ashing
EuroFIR guidelines for assessment of Methods of Analysis
_________________________________________________________________________________
Methods of analysis
70/70
Table 27. Codex Stan Recommended methods of analysis
Matrix
Method Reference Principle Type
Fruit juices AOAC 969.32 Codex general
method)
Atomic absorption
spectrophotometry
II
Fruit juices AOAC 986.15 (Codex general
method)
Atomic absorption
spectrophotometry
III
Vinegar AOAC 969.32(Codex general
method)
Atomic absorption
spectrophotometry
II
Remarks
Old Data .
o AOAC 944.09 – Colorimetric Zinc in Food
Compatibility of old data
o AAS and ICP are better techniques than colorimetric (Southgate, 2002)
o Contamination can be the major problem. The acids used should be highest
analytical quality. All glassware and plastic used should be cleaned and rinsed
according with EN 13804:2002.
Results are express frequently as weight of the element on sample dry weight, and
information on water content and method used to determine sample humidity need to
be given.
References
Cubbada, F., 2004. Inductively Coupled Plasma-Mass Spectrometry for the
determination of Elements and Elemental Species in Food: a review.J. AOAC
International, 87: 173-204
Jorhem, L. (2000). Determination of Metals in Foods by Atomic Absorption
Spectrometry after Dry Ashing: NMKL Collaborative Study. Journal of AOAC
INTERNATIONAL , 83 (5), 1204-1211
EuroFIR assistance to this method/guidelines
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