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Title: USE OF NITROUS OXIDE AS A PURGE GAS FOR AUTOMATED NITROGEN ISOTOPE ANALYSIS BY THE RITTENBERG TECHNIQUE

Author
item MULVANEY, RICHARD - UNIV OF ILLINOIS
item KHAN, SAEED - UNIV OF ILLINOIS
item SIMS, GERALD
item STEVENS, WILLIAM - UNIV OF ILLINOIS

Submitted to: Journal of Automatic Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/7/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: Research on the fate of natural and synthetic nitrogen fertilizers often involves the use of 15-N, a heavy isotope of nitrogen. The use of 15-N allows the researcher to distinguish the added nitrogen from the many other sources that are usually present, in order to determine the fate or effects of the added nitrogen. The difficulty with 15-N research is that it requires a specially equipped mass spectrometer, and analysis costs can be quite high. Recent advances in automating mass spectrometers have brought analytical costs down considerably, however some of the advancements have resulted in the use of freon gas during the process. For environmental reasons, the use of freon is discouraged when it can be avoided, and for the same reasons, sources of freon are becoming limited. In addition, freon is not routinely available in a very pure form, which causes problems with the analysis. For these reasons, a replacement for freon was sought. This paper describes the use of nitrous oxide as a replacement for freon, and the necessary modifications to the mass spectrometer that were necessary to accommodate the change. The results of the work show that nitrous oxide can readily replace freon for this application, thereby saving costs, improving analyses, and protecting the environment.

Technical Abstract: An apparatus that operates with an isotope-ratio mass spectrometer to automatically perform nitrogen isotope analyses by the Rittenberg technique was modified to permit the use of nitrous oxide (N20) instead of Freon (CC12F2 or CHC1F2) for the purging of air prior to hypobromite oxidation of ammonium-N to N2 in a plastic microplate. Analytical performance was unaffected by the modifications. Up to 768 samples can be processed in a single loading, at a rate of 6 to 12 samples per h. Within the range of 0.2 to 20 atom % 15N, isotope-ratio analyses of 50 to 200 ug of N using the automated Rittenberg apparatus (ARA) with a double-collector mass spectrometer were accurate to within 0.7% as compared to manual Rittenberg analyses of 1 mg of N using the same mass spectrometer with a dual-inlet system. Automated analyses of 20 ug of N were accurate to within 2%, and automated analyses of 10 ug of N were accurate to within 7%. The relative standard deviation for measurements at the natural abundance level (10 analyses, 20-200 ug of N) was < 0.04%.