A commercial system for automated nitrogen isotope-ratio analysis by the Rittenberg technique

A sequential sample treatment system is described that permits use of an isotope-ratio mass spectrometer for automated Rittenberg analyses of ammonium salts. This system is based on the design of McInteer and Montoya [Recent Developments in Mass Spectrometry in Biochemistry, Medicine and Environmental Research, edited by A. Frigerio (Elsevier, Amsterdam, 1981), Vol. 7, p. 343]. An x-y table and a set of valves under computer control are used to automatically perform hypobromite oxidations, introduce the N2 thus liberated to the mass spectrometer for isotope-ratio analysis, and effect spent sample pumpaway. Analyses can be performed on samples containing 20 μg of N. When operated with a Nuclide Model 3-60-RMS double-collector mass spectrometer, the standard deviation for measurements at the natural abundance level (12 samples, 50 or 100 μg of N per sample) ranged from 0.0002 to 0.000 06 at. % 15N. Throughput capacity is 100–250 samples per day, and unattended operation can continue for at least three days.