Continuous monitoring of hydrogen in flowing nitrogen gas was needed in connection with experimental work at the USAEC's National Reactor Testing Station. One of the methods investigated was emission spectroscopy, using quartz envelope electrodeless discharge tube excitation. The sample gas was passed through a cold trap to eliminate water vapor and hydrocarbon vapors before entering the discharge tube at a pressure of two mm Hg. Using a grating monochromator with photomultiplier detection set at 4861.3A hydrogen can be determined down to about 0.05% (v/v).
G. W. Dickinson and G. V. Wheeler, "An Investigation Into the Analysis of Nitrogen For Hydrogen by Emission Spectroscopy," Appl. Spectrosc. 18, 152-153 (1964)