Simultaneous determinations of the concentration and molecular weight of humic substances in environmental water by gel chromatography with a fluorescence detector

Simultaneous determinations of the concentration and molecular weight of humic substances in concentrated and unconcentrated environmental water samples by gel chromatography with a fluorescence detector were carried out. The calibration curves of humic acid and fulvic acid were linear in the concentration range of 0.1 to 10 mg/l. The relative standard deviations of humic substances were less than 10%. The concentrations of aquatic humic substances in rivers were high in the summer and low in the winter. The molecular weight of most humic substances in Katsura, Uji, Kidzu and Yodo Rivers was estimated to be about 3000 - 10000. The ratio of the higher molecular weight of humic substances was larger in the warmer season than that in the cooler season. The main origin of aquatic humic substances in river water may be humic substances from soils around the rivers.