Correlation and prediction of electron-capture response from molecular parameters

Abstract

The kinetic model of the electron-capture detector (ECD) relates the response to the fundamental properties of the capturing species. In the case of molecules which undergo reversible reactions, the important properties are the electron affinity, the rate constant for thermal electron attachment and the rate constant for ionic recombination. The direct calculation of the response has not been carried out because of the limited number of experimental values. In this paper, the available molecular electron affinities are correlated with the reversible half wave reduction potentials in aprotic solvents for these compounds in order to provide additional electron affinities to calculate ECD response factors. Examples of this procedure are given for data on aromatic hydrocarbons, aldehydes and ketones determined in this laboratory; and data on substituted benzophenones, aromatic hydrocarbons and heterocyclic compounds taken from the literature. Both the magnitude and the temperature dependence are predicted. The success with these compounds suggests that the effect of substituents on half wave reduction potentials can be extended to the prediction of electron affinities and in some cases, the ECD response from the structure of these molecules.