Trace analysis by means of gas chromatography

Abstract

It can be seen from this review that gas chromatography is a method highly suitable for trace analysis. Its advantage over the other chemical and physical analytical methods is that it is a separation method which mostly yields a qualitative and quantitative result.

The high-sensitivity ionisation detectors fulfil most of the requirements of trace analysis with respect to sensitivity and often also with respect to selectivity. Particularly promising in this respect are the sodium thermionic detectors and the electron-capture detectors. The possibility of connecting specific detectors in parallel with those which yield signals for all substances, e.g. coupling of a flame-ionisation detector with one or more other detectors is also promising. The sodium thermionic detector with two burners, which is a parallel combination of two systems, and makes it possible to record with special sensitivity both substances containing phosphorus and halogens and to record the other components, deserves special attention.

Although gas chromatography is at present sufficiently equipped for highly sensitive detection of trace components, the work in this direction has not yet been completed. It is frequently the case that one is so impressed by the sensitivity of the ionisation reactions and by the modern instrumentation of detectors and apparatus, that the possibilities offered by the other analytical principles, especially the colorimetric ones, tend to be disregarded.

The sensitivity of the chromatographic method can be relatively simply increased by using some concentration process. In this respect, the most valuable methods are those which use temperature programming and the sorption-type methods of concentration of the trace components. The technique of temperature programming substantially shortens the time of analysis, brings about a narrowing of the chromatographic bands, and sometimes allows continuous operation. The sorption method for enrichment using phase equilibrium in the sorption system is specially significant for the analysis of air and gases. It eliminates one of the major problems of trace analysis, i.e. the interference from common components such as water vapour. Inverse chromatography (vacancy chromatography) appears to be advantageous for trace analysis under industrial conditions.

Trace analysis by means of gas chromatography is of fundamental importance for the solution of problems relating to air pollution and industrial hygiene; for the production and processing of pure volatile substances, especially monomers, and for modern agricultural chemistry and the foodstuff industry. There is no doubt that it will play an important role in the further investigation and control of effects that modern industrial civilisation has on living Nature. Some of the most serious problems which can be clarified by GC trace analysis are, e.g., the composition of air pollutants, residue analyses of agrochemically active substances, the induced action of several harmful agents on the origin and development of some occupational diseases etc.