Gas Chromatography - Principles and instrumentation

Like all chromatographic methods, gas chromatography (GC) is a separation method. It is based on the differential migration of the constituents of the mixture to be analyzed, in a separation column containing a stationary phase. The stationary phase is generally deposited as a very thin film (µm thick) on the inner surface of the column, a long capillary tube of fused silica wound on a support. This migration takes place under the effect of a gaseous mobile phase called carrier gas. The special feature of this process is that it operates entirely on volatilized products. This means maintaining the column at a suitable minimum temperature, while preventing thermal degradation of the stationary phase and the compounds to be separated.

Since its invention in the mid-20th century (the first publication by Erika Cremer dates back to 1951, but the invention of the technique is often attributed to Martin and Synge), it has become the method of choice for separating volatile molecules. This is explained in [P 1 486] , which describes its applications in flavors, fragrances, the oil and food industries, health, the environment and pollution, etc.

In addition to the separation itself, gas chromatography requires a number of elements that are essential for obtaining the analyses: a sample injection system, chosen from the various commercially available options, to enable the sample to be introduced into the column according to its nature, and at least one on-line detection system for the separated compounds. Numerous detectors can be used, but gas chromatography, in conjunction with mass spectrometry, is a very powerful technique for analyzing complex mixtures. This combination enables the identification and quantification, even at trace levels, of species contained in a sample, thanks to the combination of its high separation power and detection sensitivity.

The processing and use of results is made even more efficient by the use of instrument control software, which offers ever more functions to simplify the user's task. As a result, a considerable amount of data can now be accessed from a chromatogram obtained with high resolution, in terms of separation, detection and identification, by comparison with mass spectra databases.

On the other hand, in routine or on-site control, the technique must be able to be used on a daily basis, by people whose expertise does not lie in separative methods. This calls for turnkey, "push-button" analysis equipment,...