An innovative method for measuring hydrogen and deuterium: Chemical reaction interface mass spectrometry with nitrogen reactant gas

A new method for measuring deuterium isotopic enrichment with CRIMS (chemical reaction interface mass spectrometry) is described. Using nitrogen as the reactant gas in a chemical reaction interface generates molecular hydrogen that provides the H2 and HD from which the deuterium content can be analyzed with a benchtop quadrupole mass spectrometer. Samples of deuterated leucine in unlabeled leucine were used as the primary test species. Detection of deuterium enrichment was accurate, precise, and linear. We used this scheme to evaluate the results of a process to acetylate lysine residues in a peptide-neurotensin. With separation on a C18 column, we found a 61% yield of the desired monoethylated product that had a D/H ratio very close to the theoretical one. Isotope ratio monitoring for deuterated species will be important in metabolism studies where CRIMS generates a comprehensive and quantitative view of products of deuterated precursors. Where concerns about metabolic isotope effects of deuterium are absent, the use of deuterium will enable these studies to be performed with simpler syntheses and at less cost than if using 13C or 15N.