Chapter 10 Environmental applications of the electron-capture detector — pesticides

Abstract

The various types of electron-capture detectors (ECDs) that have been commercially available for pesticide residue work differ in ionizing source used, design of the detector cell, and the different modes of electrical stimulation and measurement, with each of these parameters having a profound effect on the performance of the ECD. Historically, there have been four types of ECDs commonly used in pesticide analysis—three utilizing radioactive sources and one non-radioactive source. Foils with 3 H imbedded in titanium were the only type available in the past years and, therefore, these have been the traditional source of β -particles which ionize the carrier gas, generally argon, helium or nitrogen, to produce electrons. The 3 HTi sources are characterized by high specific activities which resulted in a large standing current and increased sensitivity and linear range when compared to sources employing other radioisotopes. Because 3 H is easily lost from these foils the upper operational temperature limit is 225°C which results in the foil being extremely susceptible to contamination from gas chromatography (GC) column eluates. The d.c. mode of operation is also subject to instability and anomalous responses such that the d.c. mode characteristically exhibited drifting baselines, sensitivity variations, and limited dynamic range.