Characterization and modification of the molecular weight distribution within dissolved organic matter using flow field‐flow fractionation

Abstract

AbstractDissolved organic matter (DOM) exists ubiquitously in the aquatic environment with varying chemical compositions and a wide molecular weight (MW) distribution, which, as a result, exhibits differing impacts on the behavior and fate of contaminants. The current methods for the MW characterization of DOM usually possess some weaknesses and therefore, some novel techniques are needed. In this study, the feasibility and sensitivity of flow field‐flow fractionation (FlFFF) system were studied for the MW characterization of DOMs from various origins. The systematic evaluation of FlFFF indicated that a mobile phase consisting of 10 mM NaCl and 5 mM H3BO3 and with a pH of 8 was optimal, and the fractionation program with a cross‐flow rate of 2 mL/min and a focusing time of 2 min resulted in the most efficient MW fractionation. Compared to natural waters, the standard DOM materials possessed a high proportion of humic‐like substances and narrow MW distribution. The quantification analysis showed that chromophoric organic ligands were mainly distributed in the high (i.e., 100 kDa–0.45 μm) and low (i.e., 0.3–1 kDa) MW fractions for natural waters, but in the medium (i.e., 1–100 kDa) and low MW fractions for the standard DOM materials. However, the fluorescent humic‐like substances were predominantly distributed within the medium and low MW fractions, irrespective of DOM types. This study showed the feasibility and sensibility of FlFFF in fractionating DOM samples, and can be used to quantify the different MW distribution of chromophoric and fluorescent components in standard and natural DOM.