Gas chromatography (GC), or, more recently, gas-liquid chromatography, is based on the volatilization of thermally stable analytcs which have a vapour pressure of approximately 0.1 mm or greater at temperatures less than 400°C. It is one of die outstanding and more rcccnt methods which have revolutionized the chemical analysis of major and minor components (analytcs) for both organic and inorganic analyses. Tracc organic analysis comprises the area of greatest application for gas chromatography, but there arc several GC techniques available for inoiganic pollutants. Some of the inorganic constituents may be relatively involatilc and may also be of fairly high molccular weight. Special sampling and processing techniques may be used in such cases, and these includc pyrolysis, dcrivatization, and the indirect analysis of reaction products. A promising area for tracc analysis of inorganic constituents involves the conversion of the tracc clement to a chelate compound or organomctallic and subsequent GC determination using electron capturc detection. A flame photometric dctcctor can also be used in GC for metal-containing compounds. The time required for chemical analysis using GC is normally from a few minutes to half an hour. However, for some complcx samples, the time involved in sample separation, quantitative data reduction, and sample identification can extend for several hours. The accuracy of GC analysis is governed by the sampling and injection procedures, attainable resolution, the dctcctors and dctcctor calibrations, peak area measurements, and the availability of suitable standards for GC. The precision attainable depends greatly on the particular analytical chemist's cxpcricncc and also varies for different concentration levels.
In rcccnl years, the versatility of GC has been greatly extended by the so-called ancillary techniques. This refers to the coupling of different instrumental or chcmical methods with GC in one unified system. Examples arc the coupling of GC with infrared and Raman spectroscopy, mass spectrometry, NMR spectroscopy, thin-layer chromatography, microrcactor systems, and pyrolyzcrs.