A Study on the Simultaneous Determination of Nitrogen Content and 15N Isotope Abundance in Plants Using Peak Height Intensities at m/z 28 and 29

A method for simultaneous determination of nitrogen content and 15N isotope abundance in plants was established by Elemental analysis-gas isotope ratio mass spectrometry. Taking poplar leaves and L-glutamic acid as standards, nitrogen content was determined using the standard curve established by weighted least square regression between the mass of nitrogen element and the total peak height intensity at m/z 28 and 29. Then the 15N isotope abundance was calculated with the peak height intensity at m/z 28 and 29. Through the comparison of several sets of experiments, the impact of mass discrimination effect, tin capsule consumables, isotope memory effect, and the quality of nitrogen on the results were assessed. The results showed that with a weight of 1/x2, the standard curve has a coefficient of determination (R2) of 0.9996. Compared to the traditional Kjeldahl method, the measured nitrogen content deviated less than 0.2%, and the standard deviation (SD) was less than 0.2%. Compared to the sodium hypobromite method, the 15N isotopic abundances differed less than 0.2 atom%15N, and the SD was less than 0.2 atom% 15N. The established method offers the advantages of being fast, simple, accurate, and high throughput, providing a novel approach for the simultaneous determination of nitrogen content and 15N isotope abundance in plant samples.