Keywords: high resolution mass spectrometry Systems: groundwater Substances: Acesulfame (YGCFIWIQZPHFLU-UHFFFAOYSA-N) 5-Fluoro Cytosine (XRECTZIEBJDKEO-UHFFFAOYSA-N) 2-amino-4-6-dimethoxypyrimidine (LVFRCHIUUKWBLR-UHFFFAOYSA-N) 1-Propanesulfonate (KCXFHTAICRTXLI-UHFFFAOYSA-N)