Bitesize has changed! We're updating subjects as fast as we can. Visit our new site to find Bitesize guides and clips - and tell us what you think!

Science

Chromatography

Print

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.

Audio

boy smiling wearing headphones

Science Audio Bites

Put down that pen and listen to some Science audio.

More audio

Play

Mia Cadaver illustration

Mia Cadaver's Tombstone Timeout

Revision topics from beyond the grave!

More games

BBC © 2014 The BBC is not responsible for the content of external sites. Read more.

This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.