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23.4 What is Column Chromatography?




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This article is from the Chemistry FAQ, by Bruce Hamilton B.Hamilton@irl.cri.nz with numerous contributions by others.

23.4 What is Column Chromatography?

Column chromatography consists of a column of particulate material such as
silica or alumina that has a solvent passed through it at atmospheric or low
pressure. The separation can be liquid/solid (adsorption) or liquid/liquid
(partition). The columns are usually glass or plastic with sinter frits to
hold the packing. Most systems rely on gravity to push the solvent through.
The sample is dissolved in solvent and applied to the front of the
column. The solvent elutes the sample though the column, allowing the
components to separate based on adsorption ( alumina, hydroxyapatite) or
partition ( cellulose, diatomaceous earth ). The mechanism for silica
depends on the hydration. Traditionally, the solvent was non-polar and the
surface polar, although today there are a wide range of packings including
bonded phase systems. Bonded phase systems usually utilise partition
mechanisms rather than adsorption. The solvent is usually changed stepwise,
and fractions are collected according to the separation required, with the
eluted solvent usually monitored by TLC.

The technique is not efficient, with relatively large volumes of solvent
being used, and particle size is constrained by the need to have a flow of
several mls/min. The major advantage is that no pumps or expensive equipment
are required, and the technique can be scaled up to handle sample sizes
approaching a gram in the laboratory. The technique is discussed in detail
in Heftmann [1].

 

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