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Efficient Compound Extraction Techniques in Analytical Chemistry

Learn about extraction methods to move compounds selectively, simplify processes to reduce errors and losses, exploit physical properties, and control polarity using pH. Understand exhaustive extraction and advantages of liquid-liquid and supercritical fluid extraction.

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Efficient Compound Extraction Techniques in Analytical Chemistry

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Presentation Transcript

  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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