NO reduction to N₂O improves nitrate ¹⁵N abundance analysis by membrane inlet quadrupole mass spectrometry

Earlier an automated sample preparation unit for inorganic nitrogen (SPIN) coupled to a membrane inlet quadrupole mass spectrometer (MIMS) was developed for automated and sensitive determination of the ¹⁵N abundances and concentrations of nitrate, nitrite and ammonium of aqueous solutions without any sample preparation. Here we describe an alternative analytical protocol to convert NO₃⁻ to N₂O instead of NO before measurement. This is advantageous because NO strongly interacts with surfaces, requires long purge times, and still shows considerable carryover between samples, all of which is avoided when N₂O is used as analyte. The sensitivity of the measurement of NO₃ ⁻ as N₂O is comparable to the earlier measurements with NO as analyte.