A major portion of the total organic halogen formed during chlorination is likely attributable to high molecular weight (MW) DBPs (above 500 Da), which may have potential adverse health effects. In this work, highly dosed chlorinated Suwannee River fulvic acid samples with and without coagulation pretreatment were separated and fractionated by using ultrafiltration (UF) and size exclusion chromatography (SEC) techniques. The SEC fractions corresponding to the high MW region were concentrated with nitrogen sparging and characterized by negative ion electrospray ionization/mass spectrometry (ESI-MS). The SEC–UV chromatograms and SEC–ESI-MS spectra show that coagulation greatly reduced the formation of high MW DBPs. It is of note that phosphate from the buffer could affect the ESI-MS characterization in 2–3 SEC fractions although most of the phosphate had been removed by UF.

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