Paper 8: Gas Chromatography for the Analysis of Exhaust Gases

Abstract

The traditional methods for the analysis of vehicle exhaust gases have never been entirely satisfactory. The recent development of gas analysis by gas chromatographic methods offers considerable improvement in accuracy, precision, and also in time required. Difficulties still arise for certain constituents, notably sulphur dioxide and oxides of nitrogen, for which chemical methods of analysis are still preferred. The chromatographic analysis of the hydrocarbon fraction and the remaining inorganic fraction of exhaust gases, where this is required, is now a routine operation, calling for neither expert chromatographic knowledge, nor exceptional skill in manipulation. A typical gas Chromatograph may be considered as comprising a number of simple building blocks, including a carrier gas flow system, a sample inlet mechanism, a chromatographic material for component resolution, a detector for those components of interest, and a display mechanism. Some form of electrical control is required; this may amount to little more than a Wheatstone bridge network, or may be a high quality linear amplifier and associated voltage-decade supply for the more sophisticated ionization detectors. Each of these building units is considered in detail, and the errors that can arise in the course of making an analysis of an exhaust gas are noted. The possibility of gross errors arising from defective equipment is also considered.