Chromatography

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Slide 1

Chemical Ideas 7.6

Chromatography

Slide 2

The general principle.

Use – to separate and identify components of mixtures.

Several different types - paper, thin layer, gas-liquid.

All use the principle of “partition” - affinity between two phases, to separate mixtures of substances.

Stationary phase & mobile phase.

Compounds with greatest affinity for mobile phase travel further.

Slide 3

All chromatography needs:

support material – stationary phase

solvent (or carrier gas) – mobile phase.

Slide 4

Thin Layer Chromatography - t.l.c.

Series of spots forms

Compare samples in mixture with known substances.

Measure Rf values.

Coloured compounds & colourless compounds.

Slide 5

Separation and identification.

Slide 6

Gas - Liquid Chromatography G.l.c.

Slide 7

What happens in practice.

Compounds that have high affinity for mobile phase emerge first, (most volatile).

Chromatogram charts recorder response against time.

Each component - separate peak.

Retention time – characteristic of the compound under given conditions.

Slide 8

Factors affecting retention time:

length of column

packing material

type of carrier gas

flow rate of carrier gas

temperature of column.

Slide 9

Interpreting the trace

Calibration – known compounds are added to the column and conditions kept constant.

Amount of substance – area under peak / peak height.

Relative proportions can be determined.

Slide 10

Uses of G.l.c.

Very sensitive - small quantities of substances detected, explosives, drugs etc.

Separation of pure substances for collection.

Can be connected to mass spectrometer for direct identification of substances.