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