Method validation for combined δ15N and δ18O analysis of nitrate in surface and groundwater samples

δ15N and δ18O analysis of nitrate in surface and groundwater can be successfully used for nitrate source apportionment. Currently, different sample preparation methods and isotope ratio mass spectrometry (IRMS) methods are being used for δ15N and δ18O analysis of nitrate. In this study we validated a method for combined δ15N and δ18O analysis of nitrate in water samples. More specifically we (1) optimized the operational settings of a TC/EA-IRMS system for combined δ15N and δ18O analysis, (2) compared precision and accuracy of δ15N analysis by TC/EA-IRMS and EA-IRMS, (3) compared precision and accuracy of three existing sample preparation methods and (4) estimated the uncertainty on the δ15N and δ18O analysis of nitrate in water samples.