electron capture detector in gas chromatography

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 $10 −12$ . The linear dynamic range may be $10 4$ 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