The applicability of a PALL tangential flow filtration (TFF) system for size fractionation of natural dissolved organic matter was investigated. The performance of polyethersulfone membranes with nominal molecular weight cut-off of 1 kDa, 5 kDa and 50 kDa was examined for isolation of low and high molecular weight compounds in fresh and estuarine waters with diverse physico-chemical properties. Detailed protocols for operating the TFF- system and for membrane cleaning are proposed. The ultrafiltration membranes can be efficiently cleaned to provide low carbon blanks (<0.09 mg/l). Standard colloid tests confirmed that the higher molecular weight compounds were isolated in the retentate and the lower molecular weight compounds remain in the permeate. Mass balance of fractionated natural samples showed good recoveries for dissolved organic carbon (DOC) (99±13% (1 kDa); 103±20% (5 kDa); 94±14% (50 kDa) (n=9). Moreover, high ionic strength or high DOC content did not enhance either fouling or contamination of the membrane. These findings demonstrate that the PALL TFF system is reliable for natural organic colloids fractionation in aquatic systems across both salinity and DOC gradients.

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