Development of a Detector for Ultratrace Nitrogen in Argon Using Low-Pressure, Capillary Glow Discharge Molecular Emission Spectrophotometry

Abstract

A highly sensitive detector was developed for determining parts per billion of nitrogen in high-purity argon. The method is based on the spectrophotometric determination of the emission intensity from the nitrogen molecule excited in the lowest vibrational transitions of the electronic C(3)Π(u) → B(3)Π(g) system. A capillary glow discharge technique was applied to excite nitrogen in an argon flow at several Torr. The low-pressure, capillary glow discharge method offered high sensitivity for detecting trace nitrogen in argon. The response of the detector was proportional in the range of nitrogen concentrations from 0.1 ppb, which correspond to S/N = 3, to 100 ppm.

A Low-Power, Atmospheric Pressure, Pulsed Plasma Source for Molecular Emission Spectrometry

“…However, even at a flow rate of 5.0 L/min, weak N 2 bands still exist. Since it is very unlikely that the N 2 bands at such a high flow rate are contributed by the back-diffusion of air into the detector, the nitrogen bands are probably due to the trace impurities of N 2 in helium . The influence of the back-diffusion of air can be reduced by using a higher plasma gas flow rate, reducing the inner diameter of the detector, or shielding the detector gas outlet with an optical window.…”