Photometric and electron-capture modes in a dual-channel sensor

Abstract

A simple, radioactive sensor was developed for potential use with gas chromatographic effluents and/or process streams. The sensor relies on earlier developed response modes of photometric detectors, particularly to (a) nitrogen in high-purity argon and (b) aroyl compounds in nitrogen. Its sole energy source is the weak β radiation from a 63Ni foil. The radiation creates not only luminescence but also ion pairs, and some of the latter can provide a second response channel for electron-capturing substances. Typical minimum detectable concentrations/amounts are 2 ppm of nitrogen in argon and 1 pg/s of benzaldehyde in nitrogen by photometry, as well as 0.1 pg/s of hexachloroethane in nitrogen by electron capture; with linear ranges of about two orders of magnitude in each case. Some analytes, e.g. fluorinated aroyl compounds in nitrogen, respond simultaneously on both channels. The sensor can also be run as a general detector (minimum detectable amount ca. 50 pg/s) by monitoring the quenching of background luminescence (the latter having been established by, for instance, a constant level of benzaldehyde in nitrogen).