Nitrogen isotope analysis of aqueous ammonium and nitrate by membrane inlet isotope ratio mass spectrometry (MIRMS) at natural abundance levels.

Rationale: Existing methods for the measurement of the N/ N isotopic composition of ammonium and nitrate are either only suitable for labelled samples or require considerable sample preparation efforts (or both). Our goal was to modify an existing analytical approach to allow for natural abundance precision levels.

Methods: Published reaction protocols were used to convert ammonium into N by NaOBr and nitrate into N O by TiCl .

NO Reduction to NO Improves Nitrate N 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 N abundances and concentrations of nitrate, nitrite and ammonium of aqueous solutions without any sample preparation. Here we describe an alternative analytical protocol to convert NO to NO 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 NO is used as analyte.

Measuring N Abundance and Concentration of Aqueous Nitrate, Nitrite, and Ammonium by Membrane Inlet Quadrupole Mass Spectrometry.

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 N abundances and concentrations of nitrate, nitrite, and ammonium in aqueous solutions without any sample preparation. The minimum N concentration for an accurate determination of the N abundance is 7 μmol/L for nitrite and nitrate, with a relative standard deviation (RSD) of repeated measurements of <1%, and 70 μmol/L with an RSD < 0.4% in the case of ammonium.

Online measurement of denitrification rates in aquifer samples by an approach coupling an automated sampling and calibration unit to a membrane inlet mass spectrometry system.

Aquifers within agricultural catchments are characterised by high spatial heterogeneity of their denitrification potential. Therefore, simple but sophisticated methods for measuring denitrification rates within the groundwater are crucial for predicting and managing N-fluxes within these anthropogenic ecosystems. Here, a newly developed automated online (15)N-tracer system is presented for measuring (N(2)+N(2)O) production due to denitrification in aquifer samples.