The application of HPLC–SEC for the simultaneous characterization of NOM and nitrate in well waters

The usefulness of HPLC–SEC for the characterization of well water quality and the identification of surface-water or wastewater percolation into wells was studied. In total, 267 private wells from rural areas of Finland, two surface waters and two wastewater effluents were analyzed for organic matter (Dissolved Organic Carbon (DOC)) and nitrate with conventional methods. High Performance Liquid Size Exclusion Chromatography (HPLC–SEC) was also used for NOM (Natural Organic Matter) and nitrate analysis. High DOC values were found occasionally in both shallow and deep wells. HPLC–SEC with UV-254 detection separated 6 fractions in the wells studied: three High Molecular Weight (HMW) fractions, two Intermediate Molecular Weight (IMW) fractions and a Low Molecular Weight (LMW) fraction. The LMW fraction is an overlap of LMW organic compounds and nitrate. In wells with a high DOC content the chromatograms were typically “surface water”-like, with HMW fractions clearly present and often dominant. Anthropogenic influence on wells was seen in the increase of LMW fraction VI, which shows an increased nitrate concentration. Nitrate concentration can be determined with precision by HPLC–SEC using UV detection at 224 nm.