FAST, AUTOMATED-ANALYSIS OF N-15 NITRATE FROM PLANT AND SOIL EXTRACTS

A batch procedure that selectively reduces NO3 from plant tissue and s oil extracts to NO for N-15 analysis has been adapted for continuous-f low, isotope ratio mass spectrometry. this provides a fast and simple method of analyzing large numbers of samples; a batch of 50 samples ca n be prepared and analyzed in under 4 h. The technique is much faster and requires smaller samples than manual determination using conventio nal mass spectrometry. Samples containing from 20 to 200 mug NO3-N wer e analyzed with a precision (standard deviation) of less-than-or-equal -to 0.001 atom % at natural abundance and almost-equal-to 0.005 atom % at 10 atom % N-15; the precision is limited more by sample preparatio n than analysis. The ability to easily determine N-15-NO3 in whole ext racts is of great help in performing N-15 labeling experiments, allowi ng short-term measurements of the N flues through key processes such a s NO3 transport and assimilation in plants or nitrification in soils.