1 CHEM 511 ADVANCED QUANTITATIVE ANALYSIS R. S. Houk, B27 Spedding, 4-9462, [email protected]...

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CHEM 511 ADVANCED QUANTITATIVE ANALYSIS

R. S. Houk, B27 Spedding, 4-9462, [email protected]

Office: 8:30 – 10 AM T Th, other hours as available

Grading: system will be usedHour exam I 25%Hour exam II 25%Final exam 30% (50% comprehensive, 50% material since last exam)Paper 20%

QUESTIONS WELCOME ANYTIME!

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NO FORMAL TEXTHARRIS, QUANT CHEMICAL ANALYSIS, 7th ED.SUGGESTED

www.chem.iastate.edu/courses.html

ACCESS TO EXCEL?

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CLASS OUTLINE

I. Overall Analytical Process

II. Sampling and Sample Preparation

III. Advanced Chemical Equilibrium

IV. Evaluation of Analytical Data, Accuracy & Precision

V. Miscellaneous Measurement MethodsImmunoassay Searching Spectral DatabasesElectrochemistry Elemental SpeciationKinetic Methods Activation AnalysisIn Situ Methods, Sensors Flow Injection AnalysisMeas. Binding Constants

VI. Scientific Writing

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PART I. OVERALL ANALYTICAL PROCESS

DEFINEPROBLEM

SELECTMETHOD

SAMPLINGSAMPLE

PREP.

MEAS.ANALYTES

EVALUATEDATA

Analyst Client

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METHOD INCLUDES ALL STEPS, NOT JUST MEASUREMENT

SOMETIMES PREPARE SAMPLE & MEAS. ANALYTES AT SAME TIME

RESULTS SOMETIMES INDICATE DEFICIENCY,TAKE & PREPARE NEW SAMPLES, EVEN RE-DEFINE PROBLEM

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DEFINE PROBLEM?

What is overall scientific question? Time constraints?- on-line meas.?

What type of anal. results needed?-qual or quant? Cost acceptable?-elements, compounds, or isotopes? -instrumentation

-personnel (usually cost more

*Nothing costs more than poor result! than insts.!)-sampling & prep.

Analysis done previously? Consult literature.General journalsSpecialty journalsReviews & monographsCompilations of official or approved methods (AOAC, EPA, …)Internet - websites, newsgroups, list servers - reviewed?

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TERMINOLOGY

ACCURACY - agreement between meas. value and actual conc.

PRECISION - reproducibility of repeated measurement

SYSTEMATIC ERROR, DETERMINATE ERROR, BIAS - all results off by consistent amount.

RANDOM ERROR, INDETERMINATE ERROR - some results too high, others too low, ~ evenly distributed.

MEAN & STANDARD DEVIATION (s) -absolute std. dev. - rel. std. dev. = s /

( )x

( )x

Confidence limits = x ts

n *Specify

n!

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CALIBRATION CURVE

SENSITIVITY = slope of cal. curve.

DETECTION LIMIT = analyte conc. or mass necessary to produce net signal = 3x (std. dev. of blank).Minimum amount of analyte that can be measured

*SENSITIVITY DETECTION LIMIT!!

SELECTIVITY - pick out analyte signal in mixture.

ONLY SAMPLES ARE ANALYZEDELEMENTS OR COMPOUNDS ARE IDENTIFIED OR DETERMINED.

SAMPLINGOBJECTIVE - to collect sample whose composition represents that of overall material to be analyzed, within acceptable limits.

Usually can’t analyze entire material, collect portion for analysis representative of whole material.

SAMPLE PREPARATIONOBJ - to convert sample into form suitable for analysis.

Usually dictated by instrument used & information required.-dissolution for elemental analysis, destroys chemical info.-organic comps. in soils extracted, then meas. by GC-MS …

Sampling & sample prep. prone to errors - loss or contamination.Best possible inst. produces wrong result if sample contaminatedor if comp. of sample analyzed that of original material!

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MEASURE ANALYTESOBJ - Select best method, optimize performance.

Usually done with instrument, even titrations.

Discuss special methods, don’t fit other courses.

EVALUATE DATAOBJ - to determine if data produced are adequate to solve original scientific problem.

Identified important analytes & potential interferences?

Detection limits?

Adequate accuracy & precision?

Do meas. results agree with “true” values? Reject outliers?

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EXAMPLE PROBLEM

Source of smuggled gold? Purely from one mine or melted & mixed? Use trace element composition to trace source of gold?

Cost of instrument insignificant relative to problem.

Gold very valuable, analyze sample directly, no dissolution, small samples.

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“Gold can be melted and recast and is therefore virtually untraceable”

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Select MethodObjective : ID elemental impurities in gold metal.

“Suspected theft!”

- Analyze solid directly, hard to dissolve. Don’t want to destroy entire sample to determine if stolen!

- Multielement measurement, ID as many elements as possible.

- May not need to quantify elements, in most cases, depends on differences in trace elements in nature.

- Need fast results. Can’t hold suspects in jail forever unless have evidence to charge them.

-Data adequate to stand up in court

Method of choice:

1. Use laser ablation to sample gold

2. Then ICP-MS to ID trace elements

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REs Much lowerREs!

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SAMPLER SKIMMER

IONLENS

ION SAMPLING INTERFACE

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SamplingOne spot may be contaminated or lacking importantelement.

Raster laser around surface of sample. Dig various pits.

When melt gold & recast, reasonably homogeneous. Probably OK just to shoot at upper layers with laser.Gold also resistant to oxidation, so upper layers

representative of whole sample.

Sample PreparationLaser ablates solid gold into small particulates, carried by

Ar stream, then atomized and ionized in ICP.In this case, actual instrument does the sample

preparation!!!

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Measure AnalytesShoot for 5-10 minutes, 10 Hz, 600 - 1200 shotsScan whole spectrum. Might be unexpected elements!ID elements from m/z values & isotope ratioAveraged results OK, ID trace element pattern of whole sample.

Evaluate DataAre trace element patterns actually different from different gold sources?Simple pattern adequate? Apply pattern recognition.If gold is mixture, pattern is linear combination of patterns of

individual gold source. Check method - analyze gold SRMs.

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Watling, Spectrochim. Acta Part B 1994, 49, 205-219.

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*Problem publishing results because didn’t quantify, didn’t use internal standard, etc.

Not necessary!! Would have been waste of time!

*Don’t produce more information than needed!

Make Decision Suspect guilty or innocent? Evidence adequate

to go to court?

Return gold to proper owner.

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Sampling & Sample Preparation

Refs: Skoog, West, Holler, Anal. Chem. SWH, 7th ed., Chap. 32, 8th ed., Chaps. 34-36.Kratochvil & Taylor, Anal. Chem. 1981, 53, 924A. (AC)

C. A. Bicking, Treatise on Anal. Chem. 2nd ed., Vol.1, Part 1, Chap. 6, pp. 299-359

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Objective: Collect sample that represents actual composition of overall material, within acceptable tolerance

representative sample

*Note: still important consideration for on-line process analysis, ie., sensors, probes, etc, that analyze sample as is w/o preparation.

Several questions: does small probe or sensor address enough sample for results to be rep. of whole?

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Main Issues:

1. Sampling error significant relative to overall error?

2. Consider particle size at which heterogeneity begins. Sample enough particles to get rep. sample? Done within context of whole method.

3. Minimize contamination & loss. More later, also related to sample prep’n

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Harris p 7

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Sampling error random std dev = sS

Analytical error random, std dev = sa

Both errors random, variances add

sD = overall std dev in means

sD2 = sa

2 + sS2

1. Useless to use very precise analytical method (small sa) with sloppy sampling (large ss)

2. If material can’t be sampled with small ss, might as well use cheaper/faster anal. method, so long as sa < ss !

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Collect Gross Sample, reduce size to analytical sample

Dictated largely by sample matrix

Matrix Size at which heterogeneity begins

Homogeneous gas or liq. Atomic / molecular

Suspended particles Size of particulate

in homo gas or liq. (colloids < 1 µm

smoke 0.1-10 µm)

Heterogeneous gas or liq. Macro scale, may need spatial

(e.g. upstream & downsteam characterization

of spill)

Gross Sample >

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Size of gross Pure metal atomic / molecular

sample Heterogeneous metal particulate / grain sizes

such as fine grainsC

Coal (v. heterogeneous) many diff. sizes & types of

particulate

analyze just one chunk v. misleading results!

Waste of time & effort unless get rep. sample

SAMPLING SOLIDS

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How much gross sample?

WR2 = Ks

W = sample mass R = RSD (%) in sample composition

Ks = sampling constant = sample mass required to limit sampling uncertainty to 1% (with 68% confidence)

Meas. Ks exp.

Signal

mass Na

ntss

170

210

250

290

0.1 1 102 5

Conf.

interval

Ks = 30 g

Same mean in each case

Sample mass, g

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Sampling

* Sample analyzed must represent overall composition of whole material, within acceptable limits.

Steps:

1. Collect gross sample - section of overall material that is large enough for composition to be representative of whole material.

2. Reduce size of gross sample to lab samplee.g., 1 kg gross sample 1 g lab sampleReduce particle size. Loss? Contamination?

3. Prepare lab sample for analysis (often dissolve)

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Size of gross sample?

Gas, liquid, solution:

-Rel. homogeneous, small sections will likely represent composition of whole.

-Easy to collect sample, only small sample required

Solid:

-Heterogeneous, individual particles prob. differ, must collect enough particles for rep. sample, so gross sample may be very large

e. g. coal

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SAMPLING STATISTICSHARRIS p 646

Mixture of particles, nA of type A & nB of type B

p = probability of drawing type A = nA/(nA + nB)

q = prob of drawing type B = nB/(nA + nB) = 1 – p

Withdraw N particles at randomSampling error = std dev = ss

Npq ss

Ex p 6461% KCl particles + 99% KNO3 particlesCollect 104 particles.How many are KCl? What is std dev of many such collections?

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Npq ss ss ~ N1/2 Rel error = ss/N ~ 1/N1/2

1. To reduce ss/N appreciably, must greatly increase N!

2. N = # of particles If particles are large, sample mass also large!

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Ex. Solid mixture of 2 types of particles (composition P1 + P2)

density d1 + d2, p = fraction of total in one form

How many of these particles (n) must be collected so that comp. of gross sample = that of total material within std dev. = sr (RSD)?

= # of particles in avg. avg.

gross sample density composition

2212

21 ))()(1(Ps

PP

d

ddppn

r

(Ch. 8 SWHC8)

Smaller sr (high accuracy)

large ( p1 - p2) (more heterogeneity)

Large n

large gross sample

Important to define problems --- what level of accuracy required? No use using larger gross sample than necessary.

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If n large, sample large solid particles, gross sample might be v. large indeed

- railroad car full for coal.

- cone & quarter many times.

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Sampling Procedures

1. Homogeneous liquids - just lower bottle cap, pull out. Or pump out through line,

esp. process stream.

2. Liquids & particulates (river waters, eg)

a) liquid only, filter out particulate

- size of pores thru filter? - may change equilibrium in supernatant

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Pb2+ sorbs readily, much of Pb in water may actually be sorbed to particles! If remove colloids, meas. [Pb] in H2O too low!

Problem? Depends on results required

Colloidal particle in H2O

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3. Gases -

a) expandable bag or balloonb) pass through filter or solvent, strip out analyte

4. Compact solids - auger or corer crush whole solid

5. Particulate solids

a) thief - slotted bottle inserted into collection of particulates

comes out with rep. material.

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Reduce size of gross sample

Instrument can't analyze massive amount of matrix.

Subdivide gross sample into smaller lots,each lot still represents overall gross sample

Often involves reducing particle size at which heterogeneity begins.e.g. grind solids

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Examples

1. Sea water (elements very low concentration)a) evaporate 1L to 5 mL, increase analyte conc. 1000/5 = 200Xb) also matrix (Na, K, Ca, Cl)

Pour 1L through chelating column, reduce size of gross sample, preconcentrate analyte,remove tough matrix, all at same time!

Then elute in ~ 2 mL.

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2. Coning and quartering coal, truckload few g! * Analyte stable during sampling? - acidify water Do additives - coagulation of blood contaminate sample? (prevent w. EDTA) sample?

Contamination Control in Trace Element AnalysisM. Zief & J. W. MitchellChemical Analysis Vol 47, Wiley

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Sample Preparation

Objective - convert lab sample to form that can be analyzed by appropriate methods with acceptable accuracy and precision.

Refs. Jarvis chap.R. Bock, Handbook of Decomposition MethodsBlackie, London, 1979.www.sampleprep.duq.edu/sampleprep/

* No single best sample preparation procedureChoice decided by requirement of overall problem.

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Why analyze sample as solution?

1. Many techniques require solution2. Solution homogeneous, simplify presentation of representative sample to instrument3. Relatively simple to prepare standards with solutions - just add aliquots of analyte elements

a) some elements incompatible (Ag+ & Cl-)b) for many elements accumulative error of pipetting adds up fast, also contamination

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4. Easy to produce blank (sample that lacks analyte), measure blank right before/after sample, evaluate correction for interference or contamination5. Procedures for producing and storing solutions well established, not perfect but problems readily anticipated.

Disadvantages of dissolving samples:

1. Time consuming and difficult, especially ceramics, refractory or noble metals

2. Can introduce additional matrix elems. & impurities

3. Destroy spatial information

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Suppose sample is already in solution, preserve until analysise.g Canadian Geo. Survey. Transport water back to instrument for analysis.

1. Stability during storage ?

Fe+3 + 3 OH- ‡Fe(OH)3 x H2O KSP

H2O ‡ H++OH- KW

If Fe(OH)3 x H2O forms, many other trace metals will coprecipitate, must acidify sample.

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* Solution for elemental analysis usually acidic during storage, and measurements usually done on acidified soln. If must make neutral or basic, sometimes OK during separation / preconcentration steps. HNO3 usually preferred

2. Leaching from or loss to container also problem:

Elemental analysis - plastic only, Teflon, no glassware!Preclean with acid & leach.

*How evaluate contamination? Measure blank! Standard additions!

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2. Correct oxidation states, other chemical forms?

e.g. Se(0) Se(IV) Se(VI) [Se(-2)]

SeO3-2 SeO4

-2 Se in proteins

Se(IV) SeH4 (g) quant.

Se(VI) SeH4 poor yield, erratic

Se(0) no SeH4

Se-proteins

Therefore, to measure total Se,

must be sure all Se present as Se(IV) first!

NaBH4 For hydridegenerationAAS

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3. Concs. high enough? If not:

a) Evaporative preconcentration.

* Avoid heat to dryness, severe loss of volatiles.

b) Preconcentration and matrix removal.

Some form of LC.

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Original sample is solid. Must dissolve.** Why dissolve sample at all? Dry first? Or analyze “as received?”

I. Dry ashing (esp. for organic samples)

- heat at high temp (maybe 600 oC), maybe also O2. - burn off org. matrix. - dissolve residue in acid. - seldom used now - many elements lost (Ag, As, Au,

Be, Cd, Co, Cs, Cu, …… Hg, Pb, …Se, Sn, Tl)!

*Always hard to reproduce partial losses. Bad idea to try to correct for low recovery.

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II. Wet Digestion in AcidA. Acids Used1) Variety of acids, dep. on how tough sample

is.2) Safety critical! Literature review or experience

essential, esp. with HClO4 & HF.

3) Refs. R. Bock, A Handbook of Decomposition Methods,

Blackie, 1979. Z. Sulcek + P. Povandra, Methods of Decomposition

in Inorganic Analysis, CRC Press, 1989.I. Jarvis, Sample Prep. for ICP-MS, in Handbook of ICP-MS, 1992.

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SAMPLE DISSOLUTION

DIGEST SOLID?ICP-MS: HNO3 , H2O2 ONLY IF POSSIBLEHF, HCl, HClO4 IF NECESSARY

SAFETY!!APPROVED PROCEDURES

MAKE UP IN AQUEOUS HNO3

TYP. 0.1 to 1% SOLUTE IN 1% ACIDKEEP ACID CONC. CONSTANT

TMAH (Me4N+OH-) IN H2OBIO. MATERIALS

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LOW BLANKS?

NALGENE OR POLYETHYLENE OK FOR DIW

TEFLON CONTAINERS PREFERREDFOR ACIDIC SAMPLES

ACID-WASH:10% HNO3 + 5% H2O2 + 5% HF (CAREFUL!!)WARM OVERNIGHT OR LONGERRINSE & STORE IN DIW

DUST-FREE ENVIRONMENTKEEP SAMPLE BOTTLES CAPPED

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CLEAN ACIDS?SUB-BOILING DISTILLATION

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Impurities in HNO3

ACS Reagent Commercial grade high-purity

Pb 0.02 0.2 0.3

Sn 0.01 0.1 1

Zn 0.04 4 8

Cr 0.05 6 130!

Cu 0.04 20 4

SB distilled

ng/g

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Clean Room - minimize contamination from particulates in atmosphere.

J. Moody, AC, 1982, 54, 1358A-1376A.

Boutron, Fresenius J. Anal. Chem. 1990, 337, 482-491.

Blower

HEPA

Hood Benches

Restrict accessPositive air pressure to outside

METAL-FREE?

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Class 10,000, 1000, 100, 10

# of particulates/unit vol.

Pb in air Fe Cu Pb Cd

St.Louis 19g/m3 Ordinary Lab. 0.2 0.02 0.4 0.002

Rural SE Mo. 0.77 Classroom 0.001 0.002 0.0002 nd

Lab. Air,NIST 0.4 Clean hood 0.0009 0.007 0.0003 .0002

* Purify acids and dissolve samples! Solution less likely to be

contaminated with dust than solid?

* Clean rooms based on semiconductor prep’n. based solely on

minimizing particulates, not metal free.

Trace Elements in ParticulatesConc, g/m3 air

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CHECK CLEANLINESS USING CAL. CURVE

Mineral Acids for Dissolving Samples for Elemental AnalysisSee Jarvis, p. 174 Table 7.1HNO3

Conc. HNO3 = 68%, 16 M, boils at 122 oC Strong oxidizing agent if present > 2 M Yields highly soluble nitrates. Little explosion danger, unless stored near organics! (Fritz group)!!!Never!!! Never!!! Nein!! Nein!! Niemals!! Niemals!!HNO3 alone: metals, alloys, bio. materials. Prefer if can get away with HNO3 alone. Tougher samples use HNO3 mixed with stronger ox. agent (H2O2 or HClO4). - HNO3 goes to work 1st, dissolves bulk of matrix. - HClO4 or H2O2 then kicks in, dissolves more refractory

residue.* Never use HClO4 alone!! Nein!! Nein!! Niemals!! Niemals!!

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HCl (12 M, 36%, bp 110oC)

Useful for many metals and oxides, esp. if form soluble chlorides (e.g. Al)Not oxidizing agent at all

Weak reducing agent, seldom used for organic materials.

Potential loss of elements with volatile chlorides (As, Sn, Pb, Hg, Se,…)

Sucks in ICP-MS, ClO+ & ArCl+

OK for most other atomic spectroscopy

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HF (29 M, 48%, azeotrope 22 M, 38%, bp 112oC)

Effective for silicates

SiO2 (s) + 6HF (aq) H2SiF6 (aq) + 2H2O

H2SiF6 (aq) SiF4 (g) + 2HF (aq)

Boil off Si from rock matrix!

Always used with oxidizing acid (HNO3 or HNO3/H2O2) High ox. states. in final solution.

V. dangerous if spilled! Need full protective clothing, protection, face shields, special cleanup kits!

Not strong acid, Ka = 6.8 x 10-4

HClO4 (azeotrope 72.4%, bp 203 oC)

Everett + Graf, Handbook of Lab. Safety, N.V. Steere, Ed.,

CRC, Cleveland.

Schumacher, J.C., Ed. Perchlorates- Their Properties,

Manufacture & Uses, ACS Mono., No. 146, Reinhold, 1960.

* Never use HClO4 alone! Nein!! Nein!! Nein!! Niemals!!

Hot, conc. azeotrope v. powerful ox. agent, explosive reaction

w. org. matter and some metals.

Cold or dilute acid little hazard.

Use HClO4 in conjunction with HNO3 (4/1 HNO3/HClO4 or more!)

- HNO3 oxidizes & dissolves most material,

then distills off at ~ 122oC.

- cold HClO4 no ox. props. until 140 oC, so doesn’t attack sample

until HNO3 boils off.

- heat further, HClO4 brings remainder of sample into solution.

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Explosion hazards

C2H5 - OClO3 + other organic perchlorates

Some dry (anhydrous) metal perchloratesesp. Mg (ClO4)2

Esp. from alcohols, fats, lipids!

Solid crystal of KClO4 or NaClO4

Inner cavity w. HClO4 or Et-OClO3,superheated

M(ClO4)n good drying agent, never use to dry org. liquid.Don’t use organic solvent in HClO4 hood!Use small amounts at first, test procedures, avoid heating to dryness.

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Periodic Table of the Elements

103Lr

(260)

102No

(259)

101Md

(258)

100Fm

(257)

99Es

(252)

98Cf

(251)

97Bk

(247)

96Cm

(247)

95Am

(243)

94Pu

(244)

93Np

(237)

92U

238

91Pa

231

90Th

232

71Lu

175

70Yb

173

69Tm169

68Er

167

67Ho

165

66Dy

162

65Tb

159

64Gd

157

63Eu

152

62Sm150

61Pm

(145)

60Nd

144

59Pr

141

58Ce

140

8A18

7A17

6A16

5A15

4A14

3A13

Lanthanides

Actinides

109Une

(266)

108Uno

(265)

107Uns

(262)

106Unh

(263)

105Ha

(262)

104Rf

(261)

89Ac

227

88Ra

226

87Fr

(223)

83Bi

209

82Pb

207

81Tl

204

80Hg

201

79Au

197

78Pt

195

77Ir

192

76Os

190

75Re

186

74W

184

73Ta

181

72Hf

178

57La

139

56Ba

137

55Cs

133

51Sb

122

50Sn

119

49In

115

48Cd

112

47Ag

108

46Pd

106

45Rh

103

44Ru

101

43Tc

(98)

42Mo

95.9

41Nb

92.9

40Zr

91.2

39Y

88.9

38Sr

87.6

37Rb

85.5

86Rn

(222)

85At

(210)

84Po

(209)

52Te

128

53I

127

54Xe

131

36Kr

83.8

35Br

79.9

34Se

79.0

33As

74.9

32Ge

72.6

31Ga

69.7

30Zn

65.4

29Cu

63.5

28Ni

58.7

27Co

58.9

26Fe

55.8

25Mn

54.9

24Cr

52.0

23V

50.9

22Ti

47.9

21Sc

45.0

20Ca

40.1

19K

39.1

18Ar

39.9

17Cl

35.4

16S

32.1

15P

31.0

14Si

28.1

13Al

27.0

2He

4.00

10Ne

20.2

9F

19.0

8O

16.0

7N

14.0

6C

12.0

5B

10.88B

2B12

1B111098

7B7

6B6

5B5

4B4

3B3

12Mg

24.3

11Na

23.0

4Be

9.01

3Li

6.94

2A2

1A1

1H

1.01 HF

HCl

ACIDS NEEDED TO KEEP ELEMENTS IN SOLUTION

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B. Regardless of acid system, microwave digestion now best heating method by far*Microwave Enhanced Chemistry, Kingston & Haswell, ACS, 1997. http://www.sampleprep.duq.edu/sampleprep1) faster (compared to conventional heating)2) better control and variation of temperature3) can often get by with less powerful acids

*Many sediments go right into solution in HNO3 with proper microwave program, never fully dissolved whenheat with hot plate in HNO3 alone, unless use HF.4) easily, safely adapted to closed vessels, minimize lossof volatile elements, see Jarvis, p. 204.*Need oven specifically designed for digestion. Can’tjust slap samples in same oven used for cooking.Microwave energy directly excites rotations, esp. of H2O

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MICROWAVE SAMPLE DISSOLUTION

SEALED VESSELSOK FOR VOLATILEELEMENTS

POWER REGULATED

SAFETY VALVES

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. Can’t dissolve sample in acid? Try flux or fusion. Ref. Zehr and Zehr, Spectroscopy 6 (4), 44 (1992-3). REQD. Also Harris p. 652

Mixture of sample and inorganic salt(usually ~ 1/10 sample/salt)

Heat mixture until melts together. Thencool and dissolve in aqueous acid or water.

Crucible (Pt, Zr, Al2O3, carbon)heat

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Li2CO3 732CNa2CO3 853 CK2CO3 903 C

Much hotter than acids!

m.p.

Particularly valuable for v. refractory materials, esp. ceramics and phosphors.Many fluxes Na2B4O7•10H2O

NaF/Na2B4O7 •10H2O Na2CO3/H3BO3

Na2CO3/Na2O2

*Different fluxes require different crucible. Some fluxes (Na2O2) eat up Pt!

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When dissolve cake, salt element present•blank of flux, evaluate contamination•problem in some meas. methods, high level of salts in subsequent solution.

*1 g sample + 9 g salt, dissolve in 1000 ml 1% total solutes

only 0.1% sample!May lose volatile elements from high temp. melt

4222 MoONaMo ONa

These procedures prob. change chemical form of analyte elements, e.g., Cr2O7

2- & Cr3+

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Related method specifically for Pt group elements(Ru, Rh, Pd, Ag, Os, Ir, Pt, Au)

Fire assay procedure*Very old --done by Egyptians for Au!Sample usually geo. matrix (suspected ore)Mix large sample (25 g) w. borax, Na2CO3, Ni, S8

Melt, physically separate NiS “button”. Pt group elements selectively dissolve in NiS buttonOther metals not.Then dissolve button soln. of Pt group elements (+ Ni).

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FLUX INFO FROM CLAISSE

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WWW.CLAISSE.COMWWW.CLAISSE.COM

Sample preparation by fusionfor AA and ICP analysis

Sample preparation by fusionfor AA and ICP analysis

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What is a fusion?What is a fusion?

Oxide

Flux

Oxide

Flux

XRFXRF

AA

ICP

AA

ICP

1050 0C1050 0C

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Examples of Fusion Solutions

Examples of Fusion Solutions

CopperCopper CeramicsCeramics

BauxiteBauxite CatalystCatalyst

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Fusion ApplicationsFusion Applications

Cements, ceramics and glassmakers• Refractories, silica, alkaline oxides, alumina, iron oxides,

magnesia, titania, zirconia...

Mining• Sulfides, fluorides, silicates, rocks, soils, ores…

Metal producers • Slags, ferroalloys, alloys and steel• Aluminum, copper, silicon, zinc...

Others• University, environmental Labs, polymers, catalysts

Cements, ceramics and glassmakers• Refractories, silica, alkaline oxides, alumina, iron oxides,

magnesia, titania, zirconia...

Mining• Sulfides, fluorides, silicates, rocks, soils, ores…

Metal producers • Slags, ferroalloys, alloys and steel• Aluminum, copper, silicon, zinc...

Others• University, environmental Labs, polymers, catalysts

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Flux: Lithium metaborate

Time: 10 min


Time: 10 min

Advantages over microwave digestion


Acids :H3PO4 and H2SO4

Time: 50 min

Acids :H3PO4 and H2SO4

Time: 50 min

Al2O3:Al2O3:

FusionFusionMicrowaveMicrowave

4 to 5x 4 to 5x fasterfaster4 to 5x 4 to 5x fasterfaster

Acids : HF and HNO3

Time: 40 min

Acids : HF and HNO3

Time: 40 min

W2O5:W2O5:

80

Step 1Acids: H3PO4 and H2SO4

Time: 60 min

Step 2Acids: HNO3 and HFTime: 35 min

Step 3Acid: H3BO3

Time: 30 min

Step 1Acids: H3PO4 and H2SO4

Time: 60 min

Step 2Acids: HNO3 and HFTime: 35 min

Step 3Acid: H3BO3

Time: 30 min



(Chromite ore)(Chromite ore)

Time: 2hrs 5 min

5 different acids

Time: 2hrs 5 min

5 different acids


Time: 10 min


Time: 10 min

FusionFusionMicrowaveMicrowave

12x Faster12x Faster12x Faster12x Faster

HNO3

Hot plate acid digestionHot plate acid digestion

•Low or partial dissolution (SiO2, TiO2…)•Low or partial dissolution (SiO2, TiO2…)

2 to 4 hr2 to 4 hrHNO3

•Extremely time consuming•Extremely time consuming

Low analytical accuracy Low analytical accuracy

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Advantages over hot plate acid digestion

Advantages over hot plate acid digestion

• Easy to use• Easy to use

High analytical accuracyHigh analytical accuracy

• Complete dissolution of the sample

• Complete dissolution of the sample

• Quick dissolution of the sample

• Quick dissolution of the sample

Time savingsTime savings

Money savingsMoney savings

12 to 20x 12 to 20x FasterFaster

12 to 20x 12 to 20x FasterFaster

83

Typical Solution Fusion Procedure – Step 1

Typical Solution Fusion Procedure – Step 1

Weigh into crucible 1.0 g LiM borate fluxWeigh into crucible 1.0 g LiM borate flux

Add 0.15 g sample ground to -200 mesh.Add 0.15 g sample ground to -200 mesh.

Add 0.20 g iodide or bromide on topAdd 0.20 g iodide or bromide on top

Heat at 1000°C while agitatingHeat at 1000°C while agitating

Rotate crucibleon inclineRotate crucibleon incline

Acid

Typical SolutionFusion Procedure – Step 2

Typical SolutionFusion Procedure – Step 2

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Claisse model “M4”Automatic Fusion Machine

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• High purity: 99.9+% and 99.99%

• Low hygroscopicity: H2O < 0,05%

• Controlled particle size: 100% < 500 m

• High fluidity and density

• Can include non-wetting agent

• High purity: 99.9+% and 99.99%

• Low hygroscopicity: H2O < 0,05%

• Controlled particle size: 100% < 500 m

• High fluidity and density

• Can include non-wetting agent

Claisse FluxesClaisse Fluxes

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• 95%Pt - 5%Au

•Rigorous quality control

•Enhanced mixing features

•Scrap precious metals buying plan

• 95%Pt - 5%Au

•Rigorous quality control

•Enhanced mixing features

•Scrap precious metals buying plan

Claisse PlatinumwareClaisse Platinumware

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PROBLEMS WITH FLUXES?

BLANK? CLEANLINESS OF FLUX MATERIAL?CLEAN UP SOLID?

RESULTING SOLN HAS HIGH DISSOLVED SOLIDS!

FLUX MATRIX INTRODUCES INTERFERING ELEMENTS?

89

NEW DEVELOPMENTS IN DISSOLUTION OF SAMPLES FOR INORGANIC ANALYSIS

1. TETRAMETHYLAMMONIUM HYDROXIDE (CH3)4NOH TMAH

DIGEST WHOLE BLOOD AT ROOM TEMP.!QUICK, SIMPLE, HIGH PURITY, LOW BLANK

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Table II. Analysis of Certified Whole-Blood Sample

Analyte InternalStandard

Meas. Conc.(µg/L)

Expected(µg/L)

Dil. FactorConc. (µg/L)

SamplePreparation

Arsenic Ge 46.4 50 50 nitric

Arsenic Ge 93.3 100 50 nitric

Arsenic Ge 143 130-195 50 nitric

Arsenic Ge 22 17-26 50 nitric

Cadmium Rh 21 18-22 50 TMAH

Lead Tb 94 92-125 50 TMAH

Lead Tb 270 254-343 50 TMAH

Lead Tb 170 170-240 50 TMAH

Mercury Tb 10 10 50 TMAH

Mercury Tb 41 50 50 TMAH

Mercury Tm 20.2 22 20 nitric



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TMAH BLANK

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Wafer Surface Preparation by VPDVapor Phase Decomposition

Wafer Surface Preparation by VPDVapor Phase Decomposition

• native oxide layer SiO2

• dissolving the native oxide layer

• soluble contaminants in fluorosilicic acid

• integral wafer contamination can be collected in one droplet

Si Wafer Analysis

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Wafer Preparation by VPD (1,2)Wafer Preparation by VPD (1,2)

Gaseous HF to SiO2 Deposition of HF(aq) film

a) b)

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Etching of SiO2 Surface Scan for Collecting Contaminants

c) d)

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e) f)

adding scanning solutionand surface scan

collection of contaminantsin one droplettransfer of droplet to ICP-MS

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VPD Calibration CurvesMCN-6000 PFA-50 ELEMENT

23Na (LR) Al (MR)

Al (LR) 44Ca (MR)

184W 48Ti

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Organic analysis usually involves extraction assample preparation step

Liquid -Liquid Extraction

Aliquot of organic solvent injected into GC

Remaining org. solvent now is itself waste!

mixorg

aq.+analyte

org.+analyte

aq

99

Solid phase extraction (SPE)N. J. K. Simpson, SPE Principles, Techniques & Applications, Marcel Dekker, 2000.

Analyte sticks to membrane,rinse out with small volumeof org. solvent.

*Much less org. waste generated than l-l extraction!*Vary chemistry of membrane, add complexing agents to sample, etc.*Eluting solvent (MeOH) can be miscible w. orig. sample (H2O)!

aq + analytethru

resin in membrane

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Simpson, p. 5.

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SOLID PHASE MICROEXTRACTION

SOLID PHASE EXT. FROM WATER

104

SOLID PHASE EXT. FROM WATER

105

SPE

STAT PHASE = SILICA + BONDED ORG PHASE (C18) POROUS POLYMER, XAD RESIN CARBON, POROUS GRAPHITIC CARBON

SOMETIMES DERIVATIZE, e.g., ION EXCHANGE SITES

SMALL STAT. PARTICLES, RAPID EQUILIBRATION, MULTIPLE EQUILIBRATIONS, EFFICIENT REMOVAL OF ANALYTE

n EQUILIBRATIONS

n1 D

1 ext.not fraction f

V

V K coeff. dist. D

aq 1,

org 2,d

* n much larger than LLE!

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SPE

USUALLY ADD AQUEOUS SAMPLEELUTE WITH SMALL VOLUMEOF ORGANIC SOLVENT

CF = CONC. FACTOR = Vsample/Veluent

MUCH HIGHER CONC. FACTORSTHAN LLE

LESS ORG. SOLVENT WASTE

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SPE IN “FILTER DISKS”

polymermembrane

Stat phase beadsimpregnated intomembrane

SHORT BED HEIGHT, 0.5 mmSMALLER PARTICLES THAN PACKED BED < 5 m, LOW BACKPRESSURESMALL Veluent, HIGH CONC. FACTORFAST, EFFICIENT

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PURGE & TRAP RECOVERY = ?

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EXTRACT INTACT COMPS. FROM SOLIDS?

SOXHLET EXTRACTION

PRESSURIZED FLUID EXT.

MICROWAVE EXTRACTION

SOFTER THAN TOTAL DISSOLUTION

Microwaves

Temp. probe

SampleSolvent

1 CHEM 511 ADVANCED QUANTITATIVE ANALYSIS R. S. Houk, B27 Spedding, 4-9462, [email protected]...

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Transcript of 1 CHEM 511 ADVANCED QUANTITATIVE ANALYSIS R. S. Houk, B27 Spedding, 4-9462, [email protected]...