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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