1

Basic Digestion Basic Digestion PrinciplesPrinciples

From Samples to SolutionsFrom Samples to Solutions

Direct Analytical MethodDirect Analytical Method

Multielement AnalysisArc/sparc OES, XRF, INAA

Solid SampleAutosampler

Mech. Sample Preparation(Grinding, Sieving, Weighing,

Pressing, Polishing, ...)

Solid Sample Problems:

• Homogeneity• Representativity• Calibration• Reference Materials• Matrix Interferences

Combined Analytical MethodCombined Analytical Method

Problems:• Time consumption• Handling steps • Error sources

Multielement AnalysisAAS, ICP-OES, ICP-MS, VA, ...

Filtration, Dilution

Decomposition

Mech. Sample Preparation(Grinding, Drying, Weighing)

Solid Sample

"Weakest link"

DefinitionDefinition

Decomposition ...

... is the transfer of a solid or liquid sample into a soluble or dissolved state for subsequent analytical characterization of its major, minor, and trace constituents.

Why Decomposition ?Why Decomposition ?

Conversion from solids into liquidsConversion from solids into liquidsDestruction of matrixDestruction of matrixSeparation of interfering substancesSeparation of interfering substancesIsoformationIsoformation of sample and standardof sample and standardHomogenizationHomogenizationPreconcentrationPreconcentration of analytesof analytes

Is there a direct analytical technique?

Decomposition: Pros and ConsDecomposition: Pros and Cons

Pros:Pros:••Leads to a representative sampleLeads to a representative sample••Reduces problems in the measurement stepReduces problems in the measurement step••Easy to standardizeEasy to standardize

Cons:Cons:••Labor intensive cost factorLabor intensive cost factor••Bottle neck in the analytical processBottle neck in the analytical process••Risk of contamination or losses of analyteRisk of contamination or losses of analyte

Spectrum of SamplesSpectrum of Samples

C

SiC ZrO

Refractories Ceramics

Mixed Waste Catalysts Ashes

Fat Grease Coal Plastics Pigments

Minerals Ores Food Pharmaceuticals Fibers

Sediments Soil Rock Glass Metals Chemicals

Water Effluents Sewage Sludge Plants Fertilizers

Decomposition must be ...Decomposition must be ...

Analytically accurateAnalytically accurate

Economically efficientEconomically efficient

Safe and easy to performSafe and easy to perform

Analytical AccuracyAnalytical Accuracy

No contaminationNo contaminationNo loss of elementsNo loss of elementsComplete decompositionComplete decompositionSmall number of working stepsSmall number of working stepsReliable equipmentReliable equipment

Reproducible analytical results

Economic EfficiencyEconomic Efficiency

Low consumption of chemicalsLow consumption of chemicalsEase of handlingEase of handlingLow investment costsLow investment costsLow operating costsLow operating costsAutomationAutomation

Costs of faulty analytical results

Time ConsumptionTime Consumption

9 % Dilution5% Weighing

26% Mechan.Preparation

5% Analysis55% Decomposition

Assumption: microwave digestion with a three fold dilution step and ICP-OES multielement analysis with three replicates.

SafetySafety

Low amounts of hazardous chemicalsLow amounts of hazardous chemicals

Simple handlingSimple handling

Spontaneous reactionsSpontaneous reactions

Protection from operator errorProtection from operator error

Instrument safety (design & manufacture)Instrument safety (design & manufacture)

Sample Digestion ...Sample Digestion ...

influences analysis time and qualityinfluences analysis time and quality

is an important economic factor in the analytical is an important economic factor in the analytical lablab

has to be optimized with respect to the has to be optimized with respect to the measuring techniquemeasuring technique

is trending towards automated, closed systems is trending towards automated, closed systems which require minimal amounts of samples and which require minimal amounts of samples and reagentsreagents

Trends in Sample PreparationTrends in Sample Preparation

Improve qualityImprove quality

Improve productivityImprove productivity

Reduce systematic handling errorsReduce systematic handling errors

High degree of automation High degree of automation at minimum costsat minimum costs

Push for onePush for one--pot or onpot or on--line techniquesline techniques

Reduce head counts in the laboratoryReduce head counts in the laboratory

Survey of Survey of Decomposition MethodsDecomposition Methods

From Solids to Liquids

Digestion Method DevelopmentDigestion Method Development

Identify sample and matrixIdentify sample and matrix

Identify Identify analyte(sanalyte(s))

Determine analysis instrumentsDetermine analysis instruments

Determine extent of digestion neededDetermine extent of digestion needed

Establish trial digestionEstablish trial digestion

Modify to improve methodModify to improve method

Test accuracy and precisionTest accuracy and precision

Decomposition StrategyDecomposition Strategy

As much as necessary, as little as possible !

Total mineralizationTotal mineralization•• Determination of Determination of

total element contentstotal element contents•• Max. requirements Max. requirements

(temperature, pressure)(temperature, pressure)•• Max. accuracy

LeachingLeaching•• Determination of soluble Determination of soluble

contents contents •• Standardized procedures Standardized procedures

(EPA, DIN, EN, ... )(EPA, DIN, EN, ... )•• ReproducibilityMax. accuracy Reproducibility

Matrix, analyte, standard procedure, analytical method, laboratory equipment?

Factors of InfluenceFactors of Influence

MatrixMatrix••Sample matrix typeSample matrix type••Reactivity Reactivity ••HomogeneityHomogeneity••Sample sizeSample size

AnalyteAnalyte••Element(sElement(s) of interest) of interest••ConcentrationConcentration••Molecular interactionsMolecular interactions••Analytes final form and Analytes final form and instrument compatibility

Reaction propertiesReaction properties••Reagent interactions at specific Reagent interactions at specific temperaturestemperatures

••Solubility and volatility of analyte Solubility and volatility of analyte & matrix components& matrix components

InstrumentationInstrumentation•• Instrument(sInstrument(s) used) used••Sample throughputSample throughput••Detection limitDetection limit••Sample introduction systemSample introduction system••Clean chemistry facilitiesClean chemistry facilitiesinstrument compatibility

Decomposition MethodsDecomposition Methods

Conv. Heating

Microwave

UV-Digestion

Open Vessel

Conv. Heating

Microwave

Closed Vessel

Conv. Heating

Microwave

Flow System

Wet Digestion

Muffle Furnace

Wickbold Comb.

Plasma Ashing

Schoeniger Comb.

Oxygen Bomb

Dynamic System

Combustion

Basic Oxidic

Fusion

Wet DigestionWet Digestion

Open systemsOpen systems•• Hot plate / block techniquesHot plate / block techniques•• Microwave heatingMicrowave heating•• UV digestionUV digestion

Closed systems ("bombs")Closed systems ("bombs")•• Conventional heatingConventional heating•• Microwave heatingMicrowave heating

Flow systemsFlow systems•• Conventional heatingConventional heating•• Microwave heatingMicrowave heating

Open Wet DigestionOpen Wet Digestion

Simple equipmentSimple equipmentHigh number of samplesHigh number of samplesLarge sample weightLarge sample weight

- High reagent consumption- Reagent blank- Contamination (dust)- Evaporation of analyte- Supervision required- Limited Temperature- Long decomposition time

Decomposition ReagentsDecomposition Reagents

HNOHNO33 Nitric AcidNitric AcidHH22SOSO44 Sulfuric AcidSulfuric AcidHH22OO22 Hydrogen PeroxideHydrogen PeroxideHClHCl Hydrochloric AcidHydrochloric AcidHFHF Hydrofluoric AcidHydrofluoric AcidHClOHClO44 Perchloric AcidPerchloric AcidHH33POPO44 Phosphoric AcidPhosphoric AcidHH33BOBO33 Boric AcidBoric Acid

Dissolution of Organic MatterDissolution of Organic Matter

Requires temp. control6

Charring & oxidation5

Increase oxidation potential( )( )4

Complexation of analytes3

Reduction of acidic strength2

Forms soluble nitrates1

RemarkH2O2HClO4H2SO4HClHNO3

This table is only a guide, it is not exhaustive!1 ... 4: Typ. closed vessel methods 5, 6: Typ. open vessel methods

Dissolution of Inorganic MatterDissolution of Inorganic Matter

(( ))(( ))Soil, sedimentsSoil, sediments

Refractory Refractory mineralsminerals

OresOres

(( ))OxidesOxides

Precious metalsPrecious metals

(( ))Metals, alloysMetals, alloys

HClOHClO44HH22SOSO44HH33POPO44HFHFHClHClHNOHNO33

This table is only a guide, it is not exhaustive!

Open vs. Closed VesselsOpen vs. Closed Vessels

closed

open

0

50

100

150

200

250

0 5 10 15 20 25

Time min.

Tem

p.°C

TOC in Open & TOC in Open & Closed VesselsClosed Vessels

0

10

20

30

40

50

60

100 120 140 160 180 200 220Reaction Temperature °C

tota

lorg

anic

car

bon

[%] Sewage sludge Soil

open vessels pressure digestion

Closed Vessel Wet DigestionClosed Vessel Wet Digestion

High temperature High temperature Short reaction timeShort reaction timeNo volatilizationNo volatilizationLess reagentsLess reagentsLess contaminationLess contamination

-- Limited sample weightLimited sample weight

Preferred Vessel MaterialsPreferred Vessel Materials

Quartz glassQuartz glass•• High temperature stabilityHigh temperature stability•• Pure and inertPure and inert•• No diffusion (preferred for Hg and hydrideNo diffusion (preferred for Hg and hydride--forming elements)forming elements)•• Chemical limitations (HF)Chemical limitations (HF)

PTFEPTFE--TFMTFM•• Universal resistance Universal resistance •• Sintered Sintered PorosityPorosity•• Temperature < 250Temperature < 250°°CC

Glassy carbonGlassy carbon•• High temperatureHigh temperature•• HFHF--applicationsapplications•• Prone to oxidationProne to oxidation

Microwave Assisted ChemistryMicrowave Assisted Chemistry

Basic microwave theoryBasic microwave theoryReaction controlReaction controlSafety considerationsSafety considerations

Why Microwave Digestion?Why Microwave Digestion?

Sample Preparation is simplifiedSample Preparation is simplified

Contamination is minimizedContamination is minimized

Retention of volatiles is assuredRetention of volatiles is assured

Complete digestion usually possibleComplete digestion usually possible

Reproducible resultsReproducible results

Sample preparation time is reducedSample preparation time is reduced

Conventional vs. MicrowaveConventional vs. Microwave

• Conduction• Convection

• Dipole rotation• Ion conduction

Conductive Heating Microwave Heating

MWMW--Assisted Sample PreparationAssisted Sample Preparation

Wet chemical decompositionWet chemical decomposition••Closed vessel systemsClosed vessel systems

••Open vessel decomposition & Kjeldahl systemsOpen vessel decomposition & Kjeldahl systems

••Flow systemsFlow systems

Sample dryingSample drying

Evaporation / concentration of solutionsEvaporation / concentration of solutions

Organic solvent extractionOrganic solvent extraction

MW muffle furnace (dry ashing)MW muffle furnace (dry ashing)

Interaction with MicrowavesInteraction with Microwaves

Conductor Reflectivee.g. metals, do not heat

Insulator Transparente.g. plastics, do not heat

Dielectric Absorptivee.g. polar liquids, heat

Microwave Principles Microwave Principles

Same Principle as a Pressure Cooker

Gas

Vapor

Liquid180°C

70°CNo MW absorption

Little MW absorption

Strong MW absorption

Cool

Hot

Closed Microwave Systems Closed Microwave Systems

+ Advantages• High temperatures

• Simple chemistry

• Fast method

• Complete mineralization

• Minimum reagents

• No loss of analyte

• Minimum contamination

- Disadvantages• Limited sample weight

• Pressure peaks

• Higher equipment costs

• More handling steps

• Two-step procedures are time-consuming

Multiwave 3000Multiwave 3000

Questions??Questions??

Q & AQ & A