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Sample Preparation and Sample Preparation and ResultsResults
ResultsResults
Mean, Median, AverageMean, Median, Average Deviation from the meanDeviation from the mean Absolute and Relative Measures: Absolute and Relative Measures: Relative = Absolute/Mean ValueRelative = Absolute/Mean Value PrecisionPrecision AccuracyAccuracy
Precision and AccuracyPrecision and Accuracy
True Value
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High PrecisionHigh Accuracy
High PrecisionLow Accuracy
Low PrecisionLow Accuracy
Low PrecisionHigh Accuracy
X‾
‾X
‾X
‾X
MethodsMethodsSensitivity – ability to discriminate between Sensitivity – ability to discriminate between small differences in analyte concentrationsmall differences in analyte concentration
Sig
nal
Amount
MethodsMethods
Detection Limit – minimum Detection Limit – minimum concentration or mass of analyte that concentration or mass of analyte that can be detected at the known can be detected at the known confidence levelconfidence level
Signal have to be 5 times bigger than Signal have to be 5 times bigger than background noisebackground noise
MethodsMethodsDynamic Range (DDynamic Range (DR)R)
DR
Sig
nal
Concentration
Analytical ProcessAnalytical Process
Systematic ErrorSystematic Error
Random ErrorRandom Error
Standards, BlanksStandards, Blanks
ResultsResults
Rounding Off (5 round to nearest even Rounding Off (5 round to nearest even digit)digit)
Significant digits (Error of measurement)Significant digits (Error of measurement) 0.1% - 0.001 x value0.1% - 0.001 x value Accuracy of measurement steps – Accuracy of measurement steps –
defines significant digitsdefines significant digits
Samples and ResultsSamples and Results
SamplingSampling RepresentativeRepresentative Homogeneous (Particles Size)Homogeneous (Particles Size) Number of Samples – Error of Number of Samples – Error of
measurement measurement
Sample preparationSample preparation
Solid – Liquid ExtractionSolid – Liquid Extraction
Matrix, solvent and analyteMatrix, solvent and analyte
Solubility of analyteSolubility of analyte
Interaction between solvent and Interaction between solvent and analyteanalyte
Soxhlet ExtractorSoxhlet Extractor1 – solvent flask1 – solvent flask2 – extractor2 – extractor3 – solvent collector3 – solvent collector4 - condenser4 - condenser
ExtractionExtraction
Factors affecting extraction:Factors affecting extraction: Interaction between solvent and analyteInteraction between solvent and analyte Distribution coefficient:Distribution coefficient:
KKDD = (m = (mii/V)/V)SolventSolvent /(m /(mii/V)/V)MatrixMatrix
Where: Where: mmii – mass of analyte – mass of analyte
V – volume of solvent and matrixV – volume of solvent and matrix
Volume of solvent vs. multiple extractionVolume of solvent vs. multiple extraction
Multiple Extraction (Oilseed)Multiple Extraction (Oilseed)
Solvent VolumeSolvent Volume Amount extractedAmount extracted Extracted (%)Extracted (%)
Single extractionSingle extraction
100 mL100 mL 0.75 g 0.75 g 7575
Multiple extractionMultiple extraction
20 mL20 mL 0.70 g0.70 g 7070
20 mL20 mL 0.26 g0.26 g 9696
20 mL20 mL 0.028 g 0.028 g 98.898.8
20 mL20 mL 0.009 g0.009 g 99.799.7
20 mL20 mL 0.0015 g0.0015 g 99.8599.85
ExtractionExtraction
Factors affecting extraction:Factors affecting extraction: Interaction between solvent and analyteInteraction between solvent and analyte Distribution coefficient:Distribution coefficient:
KKDD = (m = (mii/V)/V)SolventSolvent /(m /(mii/V)/V)MatrixMatrix
Where: mWhere: mii – mass of analyte and V – volume of solvent – mass of analyte and V – volume of solvent
Volume of solvent vs. multiple extractionVolume of solvent vs. multiple extraction Particles sizeParticles size
Liquid-Liquid ExtractionLiquid-Liquid Extraction
Distillation - extraction
GC – Sample Extraction with SolventsGC – Sample Extraction with Solvents
Methylene Chloride
Ethyl Ether
Carbon Disulfide
SPME – Solid Phase MicroextractionSPME – Solid Phase Microextraction
SPME - Fused silica fibres (1 to 2 cm long) SPME - Fused silica fibres (1 to 2 cm long) coated with various polymeric phase coated with various polymeric phase
Equilibrium forms between the three phases: Equilibrium forms between the three phases:
Fibre coating to sample phaseFibre coating to sample phase
Headspace to sample phaseHeadspace to sample phase
Fibre coating to headspaceFibre coating to headspace
SPME – Solid Phase MicroextractionSPME – Solid Phase Microextraction
SPME FibresSPME Fibres
The commercial polymeric phases available are:The commercial polymeric phases available are:
Polydimethylsiloxane(PDMS) Polydimethylsiloxane(PDMS)
Polydimethylsiloxane/divinylbenzene(PDMS/DVB) Polydimethylsiloxane/divinylbenzene(PDMS/DVB)
Polyacrylate (PA)Polyacrylate (PA)
Carbowax/divinylbenzene (CW/DVB)Carbowax/divinylbenzene (CW/DVB)
Polydimethylsiloxane/carboxen (PDMS/CAR)Polydimethylsiloxane/carboxen (PDMS/CAR)
Polydimethylsiloxane/divinylbenzene/carboxen1006 Polydimethylsiloxane/divinylbenzene/carboxen1006 (PDMS/DVB/CAR)(PDMS/DVB/CAR)
Carbowax/Templated resin (CW/TPR)Carbowax/Templated resin (CW/TPR)
SPME Adsorption and DesorptionSPME Adsorption and Desorption
http://www.chemsoc.org/exemplarchem/entries/2004/westengland_smith/ExempWeb/SPME.htm
SPE SPE Solid Phase Solid Phase Extraction - Extraction - CartridgesCartridges
Sample Preparation - SPESample Preparation - SPE
GC – Derivatization with Silyl ReagentsGC – Derivatization with Silyl Reagents
END END
Diagram of SPME ExtractionDiagram of SPME Extraction
Direct sampling SPME Headspace SPME
SPME - AdsorptionSPME - Adsorption
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