The Electron Capture Detector

Abstract

Practical problems encountered in the use of the electron capture detector have been investigated. A theoretical model is also proposed for the instrument. Detector characteristics and operating parameters are discussed and an experimental study investigated their influence on the detector response. The two principal processes occurring within the cell, electron attachment and recombination, are also discussed and partly based on the consideration of these processes, a kinetic model is proposed for the ECD. An attempt has been made to verify experimentally some of the assumptions made in the present theory and in other previous models (which have been discussed as well). The experiments included the use of electrostatic probes to determine the positive ion density in the cell, oscilloscope traces of the current pulse and current measurements on the gas outlet to observe the effect of carrier gas flow. The proposed model has shown an improvement in the prediction of the detector response observed when only pure carrier gas is flowing through the cell. It is further used to determine the electron-ion recombination coefficient for the most likely positive ion (H30+) present when moist helium is used as carrier gas.