The accurate determination of nitrogen-15 with an emission spectrometer

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Abstract
In the optical emission spectroscopic method so far used for nitrogen-15 analysis, the nitrogen in the sample is converted to N, gas by heating in a fürnace at 560°C. However, impurity gases are also easily released from the reagents CaO and CuO by this procedure. In the improved method proposed here, the nitrogen in the sample is changed to NH, gas by gentle heating with a weak flame or in a fürnace at 500°C for 1 min, after which it is converted to N2 by excitation with a high frequency generator. The procedures for the preparation of standard samples and the discharge tube, and the results obtained are described. The relation between the features of the emission and the concentration of N2 and that between the features of the spectra and the accuracy of determination were examined in detail. The accuracy of measurement was improved to ±0.002 atom % in 0.366–1.37 atom % 15N. The relationship between the actual and apparent percentage of nitrogen-15 was found to be linear on setting the same gain when the enrichment of the nitrogen-15 was less than 40%.