Topics: Chromatography, Gas chromatography, Separation process Pages: 3 (615 words) Published: May 6, 2013
The colours separate and move up the paper at different rates Chromatography can be used to separate mixtures of coloured compounds. Mixtures that are suitable for separation by chromatography include inks, dyes and colouring agents in food. Simple chromatography is carried out on paper. A spot of the mixture is placed near the bottom of a piece of chromatography paper and the paper is then placed upright in a suitable solvent, eg water. As the solvent soaks up the paper, it carries the mixtures with it. Different components of the mixture will move at different rates. This separates the mixture out.

Rf values
Different chromatograms and the separated components of the mixtures can be identified by calculating the Rf value using the equation: Rf = distance moved by the compound ÷ distance moved by the solvent The Rf value of a particular compound is always the same - if the chromatography has been carried out in the same way. This allows industry to use chromatography to identify compounds in mixtures.

Gas chromatography:
Gas Chromatography (GC) is a commonly used analytic technique in many research and industrial laboratories. A broad variety of samples can be analyzed as long as the compounds are sufficiently thermal stable and volatile enough.

How does gas chromatography work?

Like for all other chromatographic techniques, a mobile and a stationary phase are required. The mobile phase (=carrier gas) is comprised of an inert gas e.g. helium, argon, nitrogen, etc. The stationary phase consists of a packed column where the packing or solid support itself acts as stationary phase, or is coated with the liquid stationary phase (=high boiling polymer). More commonly used in many instruments are capillary columns, where the stationary phase coats the walls of a small-diameter tube directly (e.g. 0.25 mm film in a 0.32 mm...
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