https://doi.org/10.1351/goldbook.E01981
A small
radioactive source
containing 3H or 63Ni ionizes the molecules of the
carrier gas
(nitrogen or argon–methane), and a potential difference creates a small current. This current is reduced when an electronegative substance (such as a halocarbon) is introduced. The reduction in current is a measure of the concentration of the electronegative substance. The
detection limit
(threshold) varies greatly according to the substances to be analysed and can reach a mixing ratio of 1012. The linear dynamic range may be 104 but the maximum measuring value generally lies below 1 ppmv.
Source:
PAC, 1990, 62, 2167. (Glossary of atmospheric chemistry terms (Recommendations 1990)) on page 2191 [Terms] [Paper]