Organic 16: Chromatography

A family of separation techniques used to separate mixtures of substances by dissolving them in a solvent and moving it over a solid

The phase that carries the soluble components of the mixture up the stationary phase The solvent, or eluent, is the mobile phase

The phase that holds back the components attracted to it in the mixture The more affinity a component in the mixture has for the stationary phase, the slower it moves

A glass, metal, or plastic plate Coated in a thin layer of silica gel (SiO2) or alumina (Al2O3)

Whatever solvent is used

TLC moves faster Smaller amounts can be separated Spots are more compact/specific Plates are more robust than paper

Distance moved by spot / Distance moved by solvent

Using UV light Or chemical sprays (e.g. ninhydrin) which react with the spots to produce colours

Powder such as silica, aluminium oxide, or resin Packed into a narrow column

The eluent is added at the top of the column It runs down the column, bringing the components in the sample mixture with it Different substances move at different speeds And can be separated into flasks at the bottom

Acts as support for the stationary phase Ensures uniform solvent flow, preventing mixing between the stationary phase and solvent

Fairly large amounts can be separated and collected E.g. amino acids

Powder coated with oil, either packed into or coated onto the inside of a long capillary tube up to 100m long

Usually an unreactive gas such as nitrogen or helium After injection, the sample is carried along by the gas The mixture separates as some of the components move along with the gas and some are retained by the oil So the components leave the column at different times after injection (have different retention times)

Time taken for the substance to be detected

On a graph The area under each peak is proportional to the amount of each component

By comparing retention times with that of known substances under the same conditions Can confirm using mass spectrometer

Highly sensitive Can separate minute traces of substances Used to test blood or urine for presence of drugs

GCMS A mass spectrometer is used as the detector for a gas chromatography system As each component of a mixture comes out of the gas chromatography column, the time taken to pass through is noted Each component is fed automatically into the mass spectrometer

Paper chromatography Thin layer chromatography Column chromatography Gas-liquid chromatography