Size exclusion chromatography (SEC) in combination with continuous organic carbon detection (OCD) is a powerful analytical technique that enables characterization of dissolved organic water constituents. Low molecular weight organic water constituents are ubiquitous but their behaviour in SEC analyses is not yet fully clarified. Therefore, we analysed a number of low molecular weight organic model compounds with various structural and functional characteristics by size exclusion chromatography combined with online OCD and ultraviolet light absorption measurement (UVD). The detection times of some low molecular weight organic compounds were much lower than expected. Elution behaviour of low molecular weight compounds (below 300 g/mol) was determined by functional groups rather than by molecular weight. Retention times of low molecular weight compounds varied between 51.9 min, close to that of humic substances, and 235 min of benzaldehyde, the double value of a standard chromatogram runtime of 120 min. Comparisons of both detectors' signals reveal that elution times and detection times are not identical. The elution sequence of various model compounds provided here facilitates identification of peaks in the low molecular weight range of SEC chromatograms.
Keywords: humic substance, low molecular weight compound, NOM, organic carbon detection, size-exclusion chromatography