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 (chemic al reaction interface mass spectrometry) is described. Using nitrogen as th e reactant gas in a chemical reaction interface generates molecular hydroge n that provides the H-2 and HD from which the deuterium content can be anal yzed with a benchtop quadrupole mass spectrometer. Samples of deuterated le ucine in unlabeled leucine were used as the primary test species. Detection of deuterium enrichment was accurate, precise, and linear. We used this sc heme to evaluate the results of a process to acetylate lysine residues in a peptide-neurotensin. With separation on a C-18 column, we found a 61% yiel d of the desired monoethylated product that had a D/H ratio very close to t he 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 abou t metabolic isotope effects of deuterium are absent, the use of deuterium w ill enable these studies to be performed with simpler syntheses and at less cost than if using C-13 or N-15. (C) 2000 American Society for Mass Spectr ometry.