N-15-TRACER TECHNIQUE WITH THE MIP-OES DETECTION OF STABLE N-ISOTOPESFOR SOIL ECOLOGICAL-STUDIES

For soil N-transformation studies the stable isotopic N-15-tracer tech nique has been used for a long time. The ecological approach of the so il/plant/atmosphere system requires the determination of total N conte nt and stable Ni-15/N-14 isotopic ratio from large series of samples w ith various matrix composition (soil, plants, insects, etc.). A MIP-OE S method was developed for the purpose of simultaneous determination o f isotopic ratio (N-15/N-14) and total N content from the same samples . A N-2-gas generation sample introduction system was coupled with an atmospheric He-MIP. End-on viewing was applied and the N-2 band-heads were scanned in the 297- to 299-nm range by means of a monochromator o f a vibrating exit slit. The simultaneous determination of N-15/N-14 r atio and the total N content proved feasible; however, the optimum con ditions were not the same for both tasks. The method in its present fo rm is simple and has acceptable precision for routine analysis of stab le nitrogen isotopes from large series of N-15-labeled samples occurri ng in soil/plant N-cycling studies. (C) 1995 Academic Press, Inc.