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Sample Preparation and Results

Sample Preparation and Results

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Sample Preparation and Results

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  1. Sample Preparation and Results

  2. Results Mean, Median, Average Deviation from the mean Absolute and Relative Measures: Relative = Absolute/Mean Value Precision Accuracy

  3. Precision and Accuracy ‾ X ●●●●●● ●●●●●● High Precision High Accuracy ●●●●●● ‾ X ●●●●●● ●●●●●● High Precision Low Accuracy ●●●●●● ‾ X ● ● ● ● ● ● ● ● ● ● ● ● Low Precision Low Accuracy ‾ X ● ● ● ● ● ● ● ● ● ● ● ● ● ● Low Precision High Accuracy True Value

  4. Methods • Sensitivity – ability to discriminate between small differences in analyte concentration Signal Amount

  5. 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

  6. Methods • Dynamic Range (DR) Signal DR Concentration

  7. Analytical Process • Systematic Error • Random Error • Standards, Blanks

  8. 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

  9. Samples and Results • Sampling • Representative • Homogeneous (Particles Size) • Number of Samples – Error of measurement

  10. Sample preparation

  11. Solid – Liquid Extraction • Matrix, solvent and analyte • Solubility of analyte • Interaction between solvent and analyte

  12. Soxhlet Extractor1 – solvent flask2 – extractor3 – solvent collector4 - condenser

  13. 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

  14. Multiple Extraction (Oilseed)

  15. 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

  16. Liquid-Liquid Extraction

  17. Distillation - extraction

  18. GC – Sample Extraction with Solvents Methylene Chloride Ethyl Ether Carbon Disulfide

  19. 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

  20. SPME – Solid Phase Microextraction

  21. 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)

  22. SPME Adsorption and Desorption http://www.chemsoc.org/exemplarchem/entries/2004/westengland_smith/ExempWeb/SPME.htm

  23. SPE Solid Phase Extraction - Cartridges

  24. Sample Preparation - SPE

  25. GC – Derivatization with Silyl Reagents

  26. END

  27. Diagram of SPME Extraction Direct sampling SPME Headspace SPME

  28. SPME - Adsorption