Fact or Fiction: What's in your 15N2 and 15NH3 cylinders for sustainable ammonia and urea research?

Attaining reliable performance indicators via 15 N-labelling is a daunting research endeavor for sustainable ammonia and urea synthesis processes, as currently obtained reaction rates and yields are often low. However, artefact and misinterpretation can be induced by ppm-level impurities in commercial 15 N 2 and 15 NH 3 cylinders, which are not well understood. Here, we report quantitative in-line gas chromatography mass spectrometry (GC-MS) analysis of impurities in commercial 15 N 2 and 15 NH 3 cylinders at ppm level, in conjunction with 1 H-NMR methods, exemplified by 808—16252 ppm of 14 N 15 N, 2472—4891 ppm 15 NH 3 , 3—319 ppm 14 NH 3 , 0—231 ppm of 14 NO 2 , 0—176 ppm 15 NO 2 , and 0—566 ppm 15 N 16 O impurities, some of which were not reported in cylinder certification nor previous studies. The collected results have formed recommended protocols applicable to all future 15 N labelling experiments intended to eliminate false positives.