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