Characterization of the analytical performance of δ15 N and δ18 O measurements by the silver nitrate method in the framework of nitrate source apportioning.

Normalization with processed standards is essential to achieve high-precision measurements of the δ15 N and δ18 O values of nitrates extracted from unknown samples. This procedure allowed good accuracy to be guaranteed, and precision levels comparable with the observed instrumental performance to be achieved. A salt doping experiment showed a significant influence of the SO4 2- content on the δ15 N values.