Non-radioactive electron capture detector based on soft X-ray ionization for gas chromatography - A possible replacement for radioactive detectors

Abstract

In this paper, we present a new electron capture detector based on a compact X-ray tube (X-ECD) for electron generation by soft X-ray radiation instead of using a radioactive source. ECDs are commonly used in many laboratories as standard GC detectors since their invention in the 1950s, especially for highly sensitive detection of halogenated substances, pesticides or other environmental pollutants. However, due to unsatisfactory alternatives, many ECDs are still used with radioactive β-emitters, which is difficult and expensive in most applications today due to legal restrictions. The new X-ECD contains a small X-ray tube for generating free electrons by ionizing the carrier gas like in radioactive ECDs. Thus, no additional dopants or special gases are required. The X-ECD has limits of detection in the pptv range and shows linearity over a wide concentration range. Furthermore, the used X-ray tube shows good long-term stability. So far, we have operated the X-ray tube continuously for about one year without notable degradation. However, in case of future degradation, the X-ECD can still be operated with the same sensitivity by simple adjusting the set point current in constant current mode. This makes calibration robust against possible degradation of the X-ray tube. In combination with a conventional gas chromatograph, the X-ECD is able to detect halogenated hydrocarbons and even low volatile pesticides without any peak distortion such as tailing. Thereby a minimum detectability in the upper fg/µL range for Lindane was reached, which is similar when compared to radioactive ECDs.