The Design of Gas Chromatography Ionisation Detectors:A Study of the Electron Capture Detector and the Home Ionisation Detector

Abstract

Two gas ionization detectors were studied from an instrument designer's point of view. Experimental results indicate that the electron capture detector is sensitive to carrier gas density and to atmospheric oxygen. The finite conductivity of electrode insulators was also found to play an important role in the operation of the E.C.D. at high temperatures. The relation between the internal volume of a concentration detector and chromatographic peak resolution was also examined. The problem of flame ionization detector linearity and loss thereof was studied in terms of ion losses by diffusion and recombination and in terms of combustion efficiency. The effects of bias voltage and electrode spacing on the operating characteristics of the F.I.D. appear to be explainable in terms of an ion recombination hypothesis. The ultimate roll-off of the F.I.D. response curve, however, can be caused by a loss in the flame's ionization efficiency, as demonstrated by the results of a detector calibration experiment. Distortion of chromatograms due to a transfer of heat from the flame to the collector electrode was also demonstrated experimentally.