Sample Preparation and Results

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Sample Preparation and Results
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Results

• Mean, Median, Average
• Deviation from the mean
• Absolute and Relative Measures Relative
  Absolute/Mean Value
• Precision
• Accuracy

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Precision and Accuracy
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High Precision High Accuracy
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High Precision Low Accuracy
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Low Precision Low Accuracy
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Low Precision High Accuracy
True Value
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Methods

• Sensitivity ability to discriminate between
  small differences in analyte concentration

Signal
Amount
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Methods

• Detection Limit minimum concentration or mass
  of analyte that can be detected at the known
  confidence level
• Signal have to be 5 times bigger than background
  noise

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Methods

• Dynamic Range (DR)

Signal
DR
Concentration
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Analytical Process

• Systematic Error
• Random Error
• Standards, Blanks

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Results

• Rounding Off (5 round to nearest even digit)
• Significant digits (Error of measurement)
• 0.1 - 0.001 x value
• Accuracy of measurement steps defines
  significant digits

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Samples and Results

• Sampling
• Representative
• Homogeneous (Particles Size)
• Number of Samples Error of measurement

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Sample preparation
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Solid Liquid Extraction

• Matrix, solvent and analyte
• Solubility of analyte
• Interaction between solvent and analyte

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Soxhlet Extractor1 solvent flask2
extractor3 solvent collector4 - condenser
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Extraction

• Factors affecting extraction
• Interaction between solvent and analyte
• Distribution coefficient
• KD (mi/V)Solvent /(mi/V)Matrix
• Where mi mass of analyte
• V volume of solvent and matrix
• Volume of solvent vs. multiple extraction

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Multiple Extraction (Oilseed)
Solvent Volume Amount extracted Extracted ()
Single extraction
100 mL 0.75 g 75
Multiple extraction
20 mL 0.70 g 70
20 mL 0.26 g 96
20 mL 0.028 g 98.8
20 mL 0.009 g 99.7
20 mL 0.0015 g 99.85
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Extraction

• Factors affecting extraction
• Interaction between solvent and analyte
• Distribution coefficient
• KD (mi/V)Solvent /(mi/V)Matrix
• Where mi mass of analyte and V volume of
  solvent
• Volume of solvent vs. multiple extraction
• Particles size

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Liquid-Liquid Extraction
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Distillation - extraction
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GC Sample Extraction with Solvents
Methylene Chloride
Ethyl Ether
Carbon Disulfide
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SPME Solid Phase Microextraction

• SPME - Fused silica fibres (1 to 2 cm long)
  coated with various polymeric phase
• Equilibrium forms between the three phases
• Fibre coating to sample phase
• Headspace to sample phase
• Fibre coating to headspace

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SPME Solid Phase Microextraction
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SPME Fibres

• The commercial polymeric phases available are
• Polydimethylsiloxane(PDMS)
• Polydimethylsiloxane/divinylbenzene(PDMS/DVB)
• Polyacrylate (PA)
• Carbowax/divinylbenzene (CW/DVB)
• Polydimethylsiloxane/carboxen (PDMS/CAR)
• Polydimethylsiloxane/divinylbenzene/carboxen1006
  (PDMS/DVB/CAR)
• Carbowax/Templated resin (CW/TPR)

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SPME Adsorption and Desorption
http//www.chemsoc.org/exemplarchem/entries/2004/w
estengland_smith/ExempWeb/SPME.htm
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SPE Solid Phase Extraction - Cartridges
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Sample Preparation - SPE
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GC Derivatization with Silyl Reagents
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END
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Diagram of SPME Extraction
Direct sampling SPME
Headspace SPME
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SPME - Adsorption