High-pressure size exclusion chromatography analysis of dissolved organic matter isolated by tangential-flow ultrafiltration

A 1,000-Dalton tangential-how ultrafiltration (TFUF) membrane was used to i solate dissolved organic matter (DOM) from several freshwater environments. The TFUF unit used in this study was able to completely retain a polystyre ne sulfonate 1,800-Dalton standard. Unaltered and TFUF-fractionated DOM mol ecular weights were assayed by high-pressure size exclusion chromatography (HPSEC). The weight-averaged molecular weights of the retentates were large r than those of the raw water samples, whereas the filtrates were all signi ficantly smaller and approximately the same size or smaller than the manufa cturer-specified pore size of the membrane. Moreover, at 280 nm the molar a bsorptivity of the DOM retained by the ultrafilter is significantly larger than the material in the filtrate. This observation suggests that most of t he chromophoric components are associated with the higher molecular weight fraction of the DOM pool. Multivalent metals in the aqueous matrix also aff ected the molecular weights of the DOM molecules. Typically, proton-exchang ed DOM retentates were smaller than untreated samples. This TFUF system app ears to be an effective means of isolating aquatic DOM by size, but the ult imate size of the retentates may be affected by the presence of metals and by configurational properties unique to the DOM phase.