lecture 5 sample preparation. what is an extraction? move compounds of interest ‘selectively’ to...

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

OH

OHHH

OH

pH can control polarity

Acidic 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

•Expensive

Disadvantages