Gas Chromatography

Gas chromatography is a separation science tool used mainly in analytical chemistry for the separation and analysis of compounds that can be vapourised into the gas phase.

GC is similar to liquid chromatography techniques in that compounds are passed through, and bind to the functionalised surfaces of a column. However, GC differs from LC in that an inert gas, rather than a liquid, is used to elute compounds from a GC column.

During a typical GC separation, the temperature of the GC column is gradually raised and bound components are "boiled off" the column essentially in order of their boiling points. 

Eluting components can be detected by a range of methods, including flame ionisation, thermal conductance or mass spectrometry. The result is a chromatogram in which species are typically well separated.

GC involves injection of a liquid or gaseous sample onto a fused silica column coated with a microscopically thin layer of polymer or liquid. Either the entirety of a sample can be applied to column, or in split injection mode, only a portion of the sample is applied.

Initially, the sample is applied into a heated injection chamber and, after the sample is moved into the column, the volatile components condense in the column. Anything bound is removed from the column during an experiment by increasing the temperature applied to the column within an oven.

GC is the technique of choice for analytical separations of most small volatile molecules, such as mixtures of hydrocarbons and other products of the petrochemical industry, small molecule medicines and drugs of abuse, pheromones, amino acids and other small metabolites, pesticides and environmental toxins, food flavours and aromas and many others.

Some of the above applications use head space GC, which involves analysing the vapours that emit from particular samples at ambient or elevated temperatures.

GC is a highly sensitive technique and only small quantities of analyte are amenable. Hence, use of GC in detection of trace quanities of compounds in samples is common.

Typical samples can be liquids composed of volatile components, solutions in which volatile components are dissolved or solids that can emit volatile components upon heating. Gases can also be analysed.

Gases emitted from solid samples can also be analysed, often by use of a concentration step such as SPME fibre enrichment.