SETTING UP OF AN ISOTOPE ANALYZER FOR QUANTITATIVE-DETERMINATION OF PERCENTAGE ABUNDANCE OF N-15 IN NITROGEN GAS

An N-15 isotope analyser has been assembled for the quantitative determination of the percentage abundance of N-15 isotope in nitrogen gas employing molecular optical emission spectroscopic technique. The (2,0) band of the second positive system of N-2 was excited in a high frequency discharge. The band heads of the isotopic species (NN)-N-14-N-14 and (NN)-N-14-N-15 molecules were resolved using a 0.5 m monochromator and their intensity peaks were measured. The ratio of the peak heights enabled the quantitative determination of N-15 in the N-2 sample. The performance of the isotope analyser assembled was evaluated and it was found to be quite good as inferred from the analysis of primary standards. The N-15 concentration-range 0.36 to 24% is <6% and analytical error in the N rsd is <4%. A salient feature of the method adopted is that it is direct and does not call for the use of comparision standards.