Electron-capture detector kinetic model

In 1961,1 came to Houston again.. .. This provided at last an opportunity to spend full time in discovering how the electron capture detector really worked. In this I was fortunate to have nearby both Dr. Zlatkis who by then had become a close friend and colleague and Dr. Wentworth and Dr. Chen of the University of Houston. This fruitful collaboration led to the first plausible kinetic model of the electron capture detector. [2]... 

The ECD used to establish the kinetic model was custom-built. Affordable commercial ECD and negative-ion gas chromatograph chemical ionization mass spectrometers are now available. Thus in order for an investigator to use these techniques, it is simply a matter of calibrating the instrument by reproducing the experimental results to verify that no artifacts result from the equipment. The major work described in this book was conducted with the radioactive ECD. The mechanisms for the pulsed discharge electron capture detector are the same as with the radioactive ECD that is now commercially available [4]. We have used commercial detectors and a quadrupole mass spectrometer with a home-made data collection system to determine electron affinities and to study the complexes of negative ions [5-9]. 

Wentworth and Chen developed a kinetic model using a parallel-plate tritium source for the electron-capture detector that correlates observed response values with electron affinities derived from reversible half-wave potentials in aprotic... 

General models of the electron-capture process are based on the kinetic model of Wentworth and co-workers [254,293,295,298,313-315]. The ionization chamber is treated as a homogeneous reactor into which electrons are continuously introduced at a constant rate and electron-capturing solutes are added at a variable rate in a constant flow of carrier gas. The major consumption of electrons is via electron capture and recombination with positive ions. The model can be expanded to allow for the presence of electron-capturing contaminants and the formation of excited state negative ions. The kinetic model provides a reasonable explanation of the influence of pulse sampling conditions and temperature on the detector response, but exactly calculated solutions are rare. Again, this is because the necessary rate constants are usually unavailable, and the identity and relative concentration of all species present in the detector are uncertain. The principal reactions can be summarized as follows ... 

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