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Gas chromatography

In gas chromatography (GC), the mobile phase is an inert [inert: Unreactive. gas (eg helium).

The stationary phase is a very thin layer of an inert liquid on an inert solid support - such as beads of silica packed into a long thin tube (this flexible tube is coiled many times inside a thermostatically-controlled oven to keep it at a constant temperature).

GC is used to separate complex mixtures. It is much better at this than thin-layer or paper chromatography. This is because it is more sensitive - allowing the determination not only of what chemicals are in the mixture, but also how much of each chemical there is.

Carrier gas is pumped into a column oven via a flow controller. A sample is also injected into the column which is coiled inside the oven. At the other end a detector displays the result and waste is piped out

Gas chromatography

The mixture to be analysed is injected into the stream of carrier gas [carrier gas: The inert gas (often helium) used in gas chromatography to carry the mixture of substances through the column.. As it passes along the column (long thin tube) it separates into the different substances.

Substances with a greater affinity (attraction) for the mobile phase reach the detector at the end of the column more quickly. Substances with a greater affinity for the stationary phase move more slowly through the column.

Gas chromatography is used to detect banned substances in urine samples from athletes.


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