Gas chromatography is an excellent technique for the separation of the components of a mixture and for their subsequent quantitation. However, it is not easy to determine the qualitative nature of the separated components.

A number of auxiliary techniques have been employed to improve the probability of compound identification. These include: co-injection of standard compounds using colomns of different polarity, Kovats indices, log plots on single or multiple columns of different polarity to identify homologous series, specific detectors, classification of compound class by independent chemical methods either as a post-derivatization technique, or during sample work up procedures and combinations of these techniques.