Determination of ¹⁵N Isotope Abundance of Nitrite Ion in Water Samples

An isotopic abundance measurement method for ¹⁵N of nitrite ions in water samples was developed based on high-resolution gas isotopic mass spectrometry. A 2 mL sample (with nitrite ion content ≥10 mg/L), 5 mg potassium iodate and 1 ml acetic acid were taken to react and form ¹⁵NO. The generated ¹⁵NO was introduced into the high-resolution gas isotopic mass spectrometer to measure the ion flow with mass numbers 30 and 31. ¹⁵N isotopic abundance was calculated from the intensity of the two isotopic peaks. The test results showed that when the concentration of nitrite ions in the sample was ≥10 mg/L, the errors were less than 0.3%, relative standard deviation were less than 2%, while the presence of nitrate ions in the water did not affect the ¹⁵N isotopic abundance in the nitrite ions. The method was applicable to a ¹⁵N isotopic abundance range of 0.365%～99%. The method could accurately and reliably measure ¹⁵N isotopic abundance of nitrite ions in samples.