In our study, we decided to test and employ sample evaporation to increase the nitrate concentration in real water samples. Injections of 10 µL MilliQ water (blank) into the system show blank peaks of dissolved nitrogen gas in the IRMS system after 260 s under the employed conditions, which had δ 15 N values between +4 ‰ and +10 ‰ measured against the reference gas. No nitrate peak was visible in blank samples (Figure bottom right). To test if evaporation of a nitrate solution leads to isotope fractionation, we diluted (1:50) standard solutions of 50 mg L -1 KNO3 and 25 mg L -1 NaNO3 and evaporated 50 mL down to 1 mL sample volume.