Non-radioactive electron-capture detector

This paper is a review of the research that has been performed on the devel opment and applications of a non-radioactive electron-capture detector (ECD ). The ionization in the ECD, normally supplied by a radioactive foil, is s upplied by the electromagnetic radiation emanating from a high voltage puls ed discharge in pure helium. This emission consists of a broad band in the vicinity of 13.5-17.5 eV. This is a well know emission arising from a trans ition in an excited He, molecule to a dissociative ground state. The import ance of having a high energy process to initiate the ionization in an ECD i s emphasized and is the principal reason why the non-radioactive ECD perfor ms in a similar manner to the radioactive ECD. The principal advantage of t he non-radioactive ECD is the cleanliness of the detector since the gas chr omatography (GC) column effluent does not come in contact with the ionizati on source, Most radioactive ECDs generally pass the GC column effluent dire ctly over the radioactive foil where the electrons are produced from the em ission. Furthermore, the internal volume of the non-radioactive ECD can be made smaller than that of radioactive ECD using Ni-63 foils. For this reaso n, lower make-up gas flow-rates can be used and the sensitivity of the non- radioactive ECD is slightly greater than that for radioactive ECD. The temp erature dependence of the non-radioactive ECD closely parallels that of the radioactive detector. This similar behavior is the most definitive criteri on that the detectors operate in a similar manner, displaying the different types of electron attachment mechanisms. Applications to the analysis of p esticides, polychlorinated biphenyls and metal complexes have been demonstr ated along with their temperature dependence. (C) 1999 Elsevier Science B.V . All rights reserved.