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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. - PowerPoint PPT Presentation
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Lecture 5Sample
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•Random errors possible at all steps
Extractions exploit the physical properties of the compounds of
interest
Air
WaterOctanol(hydrophobic)
KAWKOA
KOW
Air
WaterOctanol(hydrophobic)
KAWKOA
KOW
SmallNon-polar
(non-interactive)
SmallPolar
(interactive)Large
Non-polar (non-
interactive)
H
H HH
O
H
HO
OH
H
H
OHOHH
H
OH
pH can control polarityAcidic
compounds
Basic compounds
Low pH (acidic)
Low pH (acidic) High pH (basic)
High pH (basic)
nonpolar
nonpolarPolar (charged)
Polar (charged)OH O-
NH2NH3+
Equilibrium vs. Exhaustive Extraction
Water
Hexane •All extractions involve an equilibrium•Exhaustive extractions usually involve repeating the process until all of the analyte is essentially in only one phase
Liquid-Liquid Extraction(Exhaustive Extraction)
100%
0%ext 1
10%
90%
initial
ext 2
1%
99%
KOW = 10
Super Critical Fluid Extraction(Exhaustive Extraction)
•Very effective•Non-toxic•Easy to remove solvent
Advantages
•ExpensiveDisadvantage
s
