CONTINUOUS-FLOW EQUILIBRATION FOR MASS-SPECTROMETRIC ANALYSIS OF DINITROGEN EMISSIONS

The measurement of denitrification in soil by the N-15 gas emission me thod requires determination of the N-2 mole masses 28, 29, and 30, Dir ect determination of N-30(2), which is not possible with all isotope m ass spectrometers, can be omitted if gas samples are equilibrated prio r to isotope analysis, Because a previously published off-line equilib ration procedure was inaccurate and laborious, a continuous-flow iv pr ocedure was developed and evaluated in this study. Analysis of N-29(2) and N-28(2) was performed with an isotope ratio mass spectrometer cou pled to an elemental analyzer. The N-2 fraction Of the samples was equ ilibrated in an electrodeless discharge unit placed within the interfa ce connecting both instruments. Measuring sensitivity for the fraction of N-15-pool-derived N-2 (d) and N-15 atom fraction of the N-15 pool (a(p)) was evaluated by analyzing N-15 standard gases at d = 5 X 10(-6 ) to 5 x 10(-4) and a(p) = 0.4903, corresponding to delta(15)N = 1.3 t o 68.3 parts per thousand. Measured values of d and a, satisfactorily coincided with theoretical values. Coefficients of variation of d and a(p) ranged from 0.13 to 19.59% and from 0.66 to 12.86%, respectively. Precision was higher than the off-line equilibration procedure and al so higher than methods including direct measurement of N-30(2).