Conservative behavior of fluorescence EEM-PARAFAC components in resin fractionation processes and its applicability for characterizing dissolved organic matter.

In this study, the applicability of the fluorescence excitation-emission matrix combined with parallel factor analysis (EEM-PARAFAC) was verified for resin fractionation processes, in which bulk dissolved organic matter (DOM) is separated into several fractions presumably having similar chemical structures. Here, four PARAFAC components, including three humic-like and one protein-like components, were identified from the EEMs of all DOM samples through fractionation procedures and the subtracted EEMs between before and after resins for different DOM sources (effluent, limnic, and riverine). The PARAFAC components exhibited conservative behavior upon resin fractionation, as indicated by the minimal difference in the PARAFAC components retained on resins calculated based on the direct subtraction of the components and the subtracted EEMs. The conservative behavior of PARAFAC components was more obvious compared with other fluorescent DOM (FDOM) indicators derived from peak-picking and fluorescence regional integration (FRI) methods. Humic-like components were more insensitive to resin fractionation than protein-like component. No consistency was found in the relative abundances of the PARAFAC components for the same resin fractions with different DOM sources, suggesting that the FDOM composition is more affected by DOM sources rather than by the resin fractions. Our study demonstrated that EEM-PARAFAC coupled with resin fractionation could provide detailed information on DOM by quantitatively comparing the individual PARAFAC components within different resin fractions.