Setting up of an Isotope Analyser for Quantitative Determination of Percentage Abundance of 15N in Nitrogen Gas

Abstract

An ¹⁵N isotope analyser has been assembled for the quantitative determination of the percentage abundance of ¹⁵N isotope in nitrogen gas employing molecular optical emission spectroscopic technique. The (2,0) band of the second positive system of N₂ was excited in a high frequency discharge. The band heads of the isotopic species ¹⁴N¹⁴N and ¹⁴N¹⁵N 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 ¹⁵N in the N₂ 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 analytical error in the ¹⁵N concentration-range 0.36 to 24% is <6% and 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.