A Methane-Conversion Detector for Gas Chromatography

Abstract

DETECTORS most commonly found in gas chromatographic instruments involve the use of thermal conductivity cells. Such cells, particularly those of the thermistor type, decrease in sensitivity with increasing temperature. Since it is necessary sometimes to heat the cell to prevent condensation effects of high-boiling materials leaving the chromato-graphic column, new approaches to this problem were sought. Martin and Smart¹ were successful in improving the sensitivity by converting the resolved compounds as they emerged from the chromatographic column into carbon dioxide and water, and detecting the carbon dioxide by means of an infra-red gas analyser. This procedure was repeated by Green² using a thermal conductivity cell to measure the carbon dioxide; however, loss of resolution and band spreading detracted from the increased sensitivity obtained. Green improved this technique by passing the water formed in the combustion process through a hot tube containing iron powder, thereby producing hydrogen, which was detected in the thermal conductivity cell. Nitrogen was the carrier gas.