DIRECT MEASUREMENT OF THE FLUORESCENCE CH ARACTERISTICS OF AQUATIC HUMIC SUBSTANCES BY A 3-DIMENSIONAL FLUORESCENCE SPECTROPHOTOMETER

Humic substances play an important role in the transport of trace meta ls and insoluble organic materials. They are also considered to be pre cursors of trihalomethane in aquatic environments. The direct measurem ent of humic substances was carried out with a three-dimensional fluor escence spectrophotometer after filtering natural-water samples throug h a GF/F glass fiber filter. Because the influence of the humic concen tration, pH and ionic strength on the three-dimensional excitation emi ssion matrix spectra is negligible, the proposed method can be directl y applied to the characterization of humic substances in freshwater sa mples (humic concentration 0.5 similar to 10 mg l(-1), pH 6 similar to 9 and ionic strength <0.04 M) and sea-water samples (ionic strength 0 .75 M). Humic substances in river, lake and pore water samples exhibit 2 similar to 3 peaks at excitation 305 similar to 340 nm/emission 415 similar to 440 nm and excitation 250 similar to 270 nm/emission 440 s imilar to 450 nm. These peak positions correspond to those of fulvic a cids isolated from soil.