Membrane inlet mass spectrometry method (REOX/MIMS) to measure 15N-nitrate in isotope-enrichment experiments

Using 15N stable isotope as a tracer to quantify N transformation rates in isotope-enrichment experiments improves understanding of the cycle various ecosystems. However, measuring 15N-nitrate (15NO3−) small volumes water for these is major challenge due inconvenience preparing samples by traditional techniques. We developed “REOX/MIMS” method applying membrane inlet mass spectrometry (MIMS) determining 15NO3− concentrations from after converting dissolved inorganic N2. The nitrates (NO3− + NO2−) were reduced NH4+ with zinc powder, and ammonium (NH4+) was then oxidized N2 hypobromite iodine solution. resulting 29N2 30N2 measured via MIMS. This optimized protocol provides sensitive (~0.1 μM) precise (relative standard deviation = 0.1–4.37%) approach (0.1–500 µM) over wide range salinities (0–35‰) 2 M KCl solution excellent calibration curves (R2 ≥ 0.9996, p < 0.0001). combined incubation measure gross nitrification NO3− immobilization It rapid, accurate, cost-effective. Future applications this efficient will inform scientists, modelers decision makers about mechanisms, sources, fates, effects delivered or produced numerous aquatic terrestrial