Parameter study of a hydrogen atmosphere flame ionization detector

Abstract

A hydrogen atmosphere flame ionization detector was constructed and operated with a direct injection technique in order to investigate detector parameters that have not previously been characterized. The optimum concentration of silane added to the hydrogen atmosphere was found to be dependent on the height of the collector electrode. At higher electrode heights, the required concentration of silane decreased. In this study, a collector height of 70 mm and a silane mixing ratio of 4 ppm were chosen as the best conditions. Also, optimal response was found when the nitrogen/ oxygen ratio was ca. 1 and when the hydrogen flow was 31/min. Several observed phenomena provided indirect evidence of the detector's mechanism. The interdependence of silane doping and electrode height supports a charge transfer process within the flame as the source of enhanced metal response. Negative peaks, observed when the off-center electrode is close to the flame, are explained as the formation of ions, via charge transfer reactions, that have reduced ionic mobilities and are more inefficiently collected by the electrode than parent ions.