Nitrate injections were performed by an HTC PAL autosampler (CTC Analytics AG, Zwingen, Switzerland) with different sizes of PEEK sample loops (5, 10, and 20 µL). The separation of nitrate from the injection peak and other potential matrix effects was achieved with a Hypercarb™ PGC column (2.1 x 100 mm, 3 µm, Thermo Fisher Scientific GmbH, Bremen, Germany) and an eluent of 0.005 M H2SO4. Furthermore, the column temperature was elevated ) for the LC-IRMS system, had been previously described in the literature and served several purposes. The copper reactor acted as an oxygen scrubber, that increased the lifetime and precision of the filament. But it is of even greater significance in this context to note the ability of heated copper to reduce gaseous nitrogen oxide species to elemental nitrogen in accordance with the following equation: