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Lecture 5

Lecture 5. Sample Preparation. What is an extraction?. Move compounds of interest ‘selectively’ to another media. Why extract?. Sampling media cannot be analyzed. Clean-up. Concentration. Why simplify extractions?. Possibility of contamination. All steps involve some loss.

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Lecture 5

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  1. Lecture 5 Sample Preparation

  2. What is an extraction? Move compounds of interest ‘selectively’ to another media.

  3. Why extract? • Sampling media cannot be analyzed • Clean-up • Concentration

  4. Why simplify extractions? • Possibility of contamination • All steps involve some loss • Random errors possible at all steps

  5. Extractions exploit the physical properties of the compounds of interest Air KOA KAW Octanol (hydrophobic) Water KOW

  6. Small Non-polar (non-interactive) Air KOA KAW Octanol (hydrophobic) Small Polar (interactive) Water KOW Large Non-polar (non-interactive)

  7. pH can control polarity Acidic compounds Low pH (acidic) High pH (basic) nonpolar Polar (charged) Basic compounds Low pH (acidic) High pH (basic) Polar (charged) nonpolar

  8. Equilibrium vs. Exhaustive Extraction • All extractions involve an equilibrium Hexane • Exhaustive extractions usually involve repeating the process until all of the analyte is essentially in only one phase Water

  9. 90% 99% ext 1 ext 2 10% 1% Liquid-Liquid Extraction (Exhaustive Extraction) KOW = 10 0% 100% initial

  10. Super Critical Fluid Extraction (Exhaustive Extraction) Advantages • Very effective • Non-toxic • Easy to remove solvent Disadvantages • Expensive

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