Why must analytes be volatile for gas chromatography?

The mobile phase is a gas, so analytes must enter and remain in the vapour phase at the column temperature; non-volatile or thermally unstable compounds are either derivatized to make them volatile or analyzed by liquid chromatography instead.

Why is gas chromatography often coupled to mass spectrometry?

Gas chromatography excels at separating complex volatile mixtures, while mass spectrometry identifies each separated component from its mass spectrum, so the combination provides both separation and confident identification.

Gas Chromatography

Gas chromatography separates volatile compounds by carrying them through a column in an inert gas stream while they partition with a stationary phase.

Definition

Gas chromatography is a separation technique in which a vaporized sample is transported by an inert carrier gas through a column, where components separate by differential partitioning between the gas and a stationary phase.

Scope

This topic covers the practice of gas chromatography: carrier gases, injection techniques, packed and open-tubular capillary columns, temperature programming, and detectors such as flame ionization, thermal conductivity, and electron capture. It addresses qualitative identification by retention and the quantitative use of peak areas, and the common coupling of gas chromatography to mass spectrometry.

Core questions

Which analytes are suitable for gas chromatography, and how are non-volatile ones derivatized?
How do capillary column dimensions and temperature programming control separation?
How do different detectors trade selectivity against universality?
How are retention times and peak areas used for identification and quantitation?

Key theories

Gas–liquid partition chromatography: Analytes vaporized into a carrier gas distribute between the gas and a liquid stationary phase coated on or in the column; differences in their partitioning produce different retention times, the principle James and Martin demonstrated for volatile fatty acids.

Mechanisms

A small volume of sample is vaporized in a heated inlet and swept onto the column by an inert carrier gas such as helium or hydrogen. As the vapour traverses the column, each analyte repeatedly partitions into and out of the stationary phase; more strongly retained analytes lag behind, so components elute at distinct times. Programmed heating sharpens later peaks. A detector at the column outlet generates a signal whose peak area is proportional to the amount of each analyte.

Clinical relevance

Gas chromatography is fundamental to environmental analysis of volatile organic pollutants and pesticides, petroleum and flavour characterization, forensic and clinical toxicology, and doping control, especially when coupled to mass spectrometry for confirmation.

History

Gas–liquid chromatography was introduced by James and Martin in 1952, extending the partition principle to volatile compounds. Marcel Golay's open-tubular capillary column in the late 1950s dramatically increased efficiency, and the subsequent development of fused-silica capillaries and selective detectors made gas chromatography a mainstay of trace organic analysis.

Key figures

Archer Martin
Anthony T. James
Marcel Golay

Seminal works

james1952
skoog2017

Frequently asked questions

Why must analytes be volatile for gas chromatography?: The mobile phase is a gas, so analytes must enter and remain in the vapour phase at the column temperature; non-volatile or thermally unstable compounds are either derivatized to make them volatile or analyzed by liquid chromatography instead.
Why is gas chromatography often coupled to mass spectrometry?: Gas chromatography excels at separating complex volatile mixtures, while mass spectrometry identifies each separated component from its mass spectrum, so the combination provides both separation and confident identification.