Occurrence of Chemical Change in the Argon Vapour Phase Chromatographic Detector

Abstract

THOUGH it is generally accepted that chemical changes occur during the operation of an argon chromatographic detector¹ the extent of change in normal operation has hitherto been assumed to be small^2,3 and to arise almost entirely from ionization, the efficiency of which, even in the triode detector⁴, rarely exceeds 1 per cent. Having examined (experimental details published in Disc. Faraday Soc., 36, 83; 1963) the breakdown of C₂ to C₆ paraffins and olefins in an argon ‘detector’ with plane parallel electrodes, we conclude that the extent of chemical reaction can be appreciable, and that excitation of the substrate gas by electron impact is largely responsible. Thus the number of molecules of n-butane decomposed per ion pair produced in such a cell (−M/N) is much greater than unity (Fig. 1), and despite the large errors which arise from the difficulty of measuring small proportions of substrate destroyed, clearly tend to increase with decrease of voltage. The same behaviour is shown by the yields of some, but not all, of the products of decomposition. It is to be expected that the average energy of electrons in the cell will fall with decreasing applied voltage, so favouring excitation of the hydrocarbon rather than that of argon, and we suggest that the results presented in Fig. 1 may be most simply explained on this basis.