Applications of Gas Chromatography

W e have chosen to illustrate the separation capabilities of GC for the analysis of volatile compounds by proposing different applications kindly provided to us by several experienced users, chosen for their sector of activity. The choice was based not only on the sector of activity and, consequently, the type of sample, but also on the conditions of sample preparation, injection and detection. The idea was to cover a wide range of techniques among those presented in [P 1 485] . However, this is only part of the range of applications for GC, as it is used in a wide variety of fields, which it was not possible to cover exhaustively in this article.

Similarly, we do not devote a separate section to qualitative and quantitative analysis. For the latter, please refer to [P 1 485] . We would simply point out that quantitative GC analysis is most often carried out using the internal calibration method when a high degree of precision is required, due to the uncertainty that exists in the volume injected from one analysis to the next.

For semi-quantitative analyses, or for a first approximation of the quantity of compounds present in the sample, we can proceed by internal normalization, either directly (the area of the desired compound is related to the total area of detected compounds), or by comparison with control compounds. The first approach assumes that all compounds in the mixture are eluted, that they are all detected, and that their response to the detection system is very similar. As indicated in [P 1 485] , this is not often the case, except for hydrocarbons with FID detection. The second approach takes a little more account of the response of different compound families, if the choice of control compounds covers the range of structures present.

The method depends greatly on the objectives of the analysis and the complexity of the samples. For samples containing more than 50 different compounds,...