Abstract
To characterize dissolved organic matter (DOM) in natural waters, a procedure called dissolved organic carbon (DOC) fractionation analysis is useful, in which DOM is fractionated into hydrophobic-hydrophilic fractions using XAD-8 resin of an acrylic ester polymer, and into acid-neutral-base fractions using ion exchange resins. However, the difficulties in XAD-8 purification and handling have limited the use of the fractionation procedure to a few research groups; thus, we have developed a new fractionation procedure using PS-2 cartridges packed with purified styrene divinylbenzene copolymer resins, instead of XAD-8. Recovery studies of model compounds such as humic and fulvic acids were conducted to compare the fractionation properties of PS-2 with those of XAD-8. The added hydrophobic and hydrophilic compounds were found at recoveries of 81∼103 % in the hydrophobic and hydrophilic fractions, respectively. The results of the recovery tests showed that PS-2 and XAD-8 have the same fractionation properties for hydrophobic DOM and hydrophilic DOM. By using a similar conditioning of PS-2 cartridges in the solid-phase extraction of the water samples, the blank DOC level in this procedure was easily reduced to 0.4∼0.5 mgC · l-1, corresponding to the levels obtained using purified XAD-8. For the repeatability of the fractionated DOC measurement, the relative standard deviation was ca. 10% when the measured DOC level was higher than threefold of the blank DOC; it was ca. 30% when the measured DOC level was between two- and threefold of the blank DOC. It was found from the data for the application to river and lake waters that the obtained composition data of hydrophobic DOM and hydrophilic DOM agreed with the reported composition data obtained using XAD-8. This procedure using PS-2 can be used for the hydrophobic-hydrophilic fractionation of DOM in natural water samples as an alternative to the conventional procedure using XAD-8.
