Keywords: high resolution mass spectrometry Systems: groundwater Substances: 5-Fluoro Cytosine (XRECTZIEBJDKEO-UHFFFAOYSA-N) Acibenzolar-S-methyl (UELITFHSCLAHKR-UHFFFAOYSA-N) Acetamipride (WCXDHFDTOYPNIE-RIYZIHGNSA-N)