Keywords: high resolution mass spectrometry Systems: groundwater Substances: 5-Fluoro Cytosine (XRECTZIEBJDKEO-UHFFFAOYSA-N) 3-Phenoxybenzoeacid (NXTDJHZGHOFSQG-UHFFFAOYSA-N) Acetochlor (VTNQPKFIQCLBDU-UHFFFAOYSA-N)