Multi‐element selective radio frequency plasma detector for capillary gas chromatography

A radio frequency plasma detector for element specific detection in gas chromatography is described. The detector is comprised of a radio frequency (300 kHz) discharge between electrodes in helium, and utilizes a low‐resolution emission spectrometer to monitor selected spectral emission lines produced when the helium discharge decomposes and excites the atomic constituents in the chromatographic column effluent. The spectrometer is tuned to an atomic emission line in the near‐infrared portion of the spectrum, and the emission intensity from the discharge region of a selected line is used to monitor the concentration of the element producing that line. Acceptable detector sensitivity was achieved by the use of a high‐throughput optical system. Selectivity was achieved by a combination of correct line selection, plasma and carrier gas purification, and plasma gas doping.