Chemical Ideas 7.6
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.
support material – stationary phase
solvent (or carrier gas) – mobile phase.
Series of spots forms
Compare samples in mixture with known substances.
Measure Rf values.
Coloured compounds & colourless compounds.
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.
length of column
type of carrier gas
flow rate of carrier gas
temperature of column.
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.
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.