Use of nitrous oxide as a purge gas for automated nitrogen isotope analysis by the Rittenberg technique

R L Mulvaney,S A Khan,G K Sims,W B Stevens

doi:10.1155/s1463924697000175

R L Mulvaney, S A Khan + Show 2 more

Open Access

https://doi.org/10.1155/s1463924697000175

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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 (N2O) instead of Freon (CCl2F2 or CHClF2) 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/h. Within the range of 0.2 to 20 atom % 15N, isotope-ratio analyses of 50 to 200 μg 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 20μg of N were accurate to within 2%, and automated analyses of 10 μg of N were accurate to within 7%. The relative standard deviation for measurements at the natural abundance level (10 analyses, 20-200 μg of N) was < 0.04 %.

Highlights

Much progress has been made during the past decade in the automation of N isotope analyses for agricultural and environmental research
N in the sample is converted to N by combustion at approximately 1700C, and a small fraction of the N2 is admitted to an isotope mass spectrometer for measurement of the ion currents at m/z 28, 29 and 30, from which total N content and atom % 15N are determined
The Rittenberg technique has been utilized in the automation of mass spectrometers for N isotope analysis

Summary

Introduction

Much progress has been made during the past decade in the automation of N isotope analyses for agricultural and environmental research. May appear to be at a considerable disadvantage relative to an ANCA-MS because of the need for wet chemical processing to convert sample N to NH--N, a method of automation based on the Rittenberg technique has several advantages for N isotope analysis.

Results

Conclusion