Our world is one of complex mixture

Our world is one of complex mixtures. Pet-roleum may well contain over 100,000 components. It is thought that there are of the order of 100,000 differe nt proteins in the human body. And natural products, such as essential oils, are also often highly complex. Separation methods are necessary to anal yse these, while even the simpler, but still often difficult, mixtures encountered in, for example, the pharmaceutical industry most often require chromatography or a related technique. Separations are achi eved by GC by a series of partitions between a moving gas phase and a stationary liquid phase held in a small diametertube (the column) after a mixture is injected as a narrow band. A detector then monitors the composition of the gas stream as it emerges from the column carrying separated compo-nents, and the resulting signals provide the input for data acquisition. GC can be applied to the analysis of mixtures, which contain compounds with boiling points from near zero to over 700 K, or which can be heated sufficien tly without decomposition to give a vap our pressure of a few mmHg. Derivatisation to increase volatility extends this range. The sample size can be as small as pg, but, in preparative, as opposed to analytical, applications, tens of grammes can be handled. GC is now a standard analytical method that underpins research, developme nt, and quality control in many industries, especially petro-chemical manu facture, and in environmen tal, food contaminant, and drug residue and foren-sic analysis.