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

For soil N-transformation studies the stable isotopic N-15-tracer technique has been used for a long time. The ecological approach of the soil/plant/atmosphere system requires the determination of total N content and stable Ni-15/N-14 isotopic ratio from large series of samples with various matrix composition (soil, plants, insects, etc.). A MIP-OES method was developed for the purpose of simultaneous determination of 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 of a vibrating exit slit. The simultaneous determination of N-15/N-14 ratio and the total N content proved feasible; however, the optimum conditions were not the same for both tasks. The method in its present form is simple and has acceptable precision for routine analysis of stable nitrogen isotopes from large series of N-15-labeled samples occurring in soil/plant N-cycling studies. (C) 1995 Academic Press, Inc.