XAD fractionation has been widely used for isolating natural organic carbon into different fractions for disinfection by-product (DBP) formation tests. The widely used Amberlite® XAD-8 resin is no longer commercially available and Supelite™ DAX-8 resin has been substituted in recent research. The objective of this study was to evaluate the differences, in terms of reactivity in DBP formation, among the dissolved organic carbon (DOC) fractions isolated by these two resins. DOC collected from two rivers and two soils in the Sacramento–San Joaquin Watershed was fractionated in parallel by the non-ionic macroporous DAX-8 and XAD-8 resins into hydrophobic and hydrophilic fractions. Four parameters used to predict DBP formation in the water industry were evaluated: specific ultraviolet absorbance at 254 nm (SUVA254), differential ultraviolet absorbance at 272 nm (ΔUVA272), specific trihalomethane formation (STHMFP) and specific haloacetic acid formation (SHAAFP). Results indicated that the sorption efficiency of DAX-8 resin was systematically greater than that of XAD-8 resin in our testing conditions and separated an average of 4% more humic substances. Hydrophobic and hydrophilic fractions isolated by XAD-8 and DAX-8 resins showed no significant difference in DBP reactivity (p>0.05), except for the hydrophilic fraction of the peat soil extracts. Our results indicated their comparability in general use for isolating DBP precursors from bulk aquatic humic substances. However, the fractions of soil humic substances, particularly organic-rich soil, isolated by these two resins may have different chemical characteristics.

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