ONLINE FRACTIONATION AND CHARACTERIZATION OF AQUATIC HUMIC SUBSTANCESBY MEANS OF SEQUENTIAL-STAGE ULTRAFILTRATION

A five-stage tangential-flow ultrafiltration (UF) device equipped with advanced membrane filters (molecular weight cut-off: 1, 5, 10, 50 and 100 kDalton) of the polyethersulfone type is described and applied fo r the analytical on-line fractionation of a series of aquatic humic su bstances (HS) originating from surface or groundwaters. Fractionation patterns of HS (6 fractions each) evaluated by this UF device exhibit their particular dependence on the HS concentration, the pH-value and the salt content of the sample (10 mi) to be analyzed. Fundamental par ameters (e.g., washing volume) governing the molecular-size fractionat ion of HS by means of multistage UF are discussed, too. The fractionat ion of an aquatic reference HS (BOG 3/9.5) by means of the above UF pr ocedure reveals considerable differences preferably characterized by t he UV-VIS absorption ratio E(350)/E(450) and metal complexing capacity (Cu(II)) of the produced fractions. Moreover, molecular spectroscopy investigations (FTIR, H-1-NMR) of the fraction series of this HS indic ate that carbohydrate substructures (preferably found in fractions >50 kDalton) and aromatic ones (preferably in fractions <5 kDalton) are u nevenly distributed.