[M-IS21_28AM2] Biogeochemistry

[MIS21-11] Pseudopolarographic estimation of copper complexing ligands in freshwater of Lake Biwa, Japan

*Masahiro MARUO¹, Hajime OBATA² (1.School of Environmantal Science, The University of Shiga Prefecture, 2.Atmosphere and Ocean Research Institute, The University of Tokyo)

Keywords:freshwater, Lake Biwa, copper, ligand, electroanalysis

Pseudopolarography (Croot P. L. et al., Mar. Chem., 67, 219-232 (1999), Wiramanaden C. I. E., et al., Mar Chem., 110, 28-41 (2008)) is useful method to detect metal (copper) complexation that is very stable compared with that detected by other methods: AdCSV: adsorptive cathodic stripping voltammetry, ion selective electrode etc. in water. It was applied in seawater analysis especially for coastal area where large amount of organic material with high complexing capacity was detected. Also in freshwater lake, there is high potential of existence of very stable copper complexes in water, as it sometimes includes high concentration of sulfur containing compounds and concentration of competing metals such as calcium and magnesium are very low compared with those in seawater. Existence of very stable ligands was investigated using freshwater sampled in Lake Biwa, Japan.As reference ligands, EDTA, DPTA and CDTA were used at pH 8.8 using borate buffer solution. Copper was deposited on HDME (hanging mercury drop electrode) by varying potential from -0.2 to -1.5 V, and deposition time was 420 s. After deposition, deposited copper was stripped by scanning from the deposition potential to 0 V. Peak height was plotted against deposition potential, and half wave potential was determined. By comparing the half wave potential with that of reference ligands, stability of copper complexing ligands in the sample was estimated.Half wave potentials measured by references were -0.4 V for EDTA, -0.58V for CDTA, and -0.65 V for DTPA, respectively. By measuring water sampled at north basin of Lake Biwa, half wave potentials at -0.5 V and -1.1 V was obtained for surface water. Only single half wave potential at -0.5 V was obtained for waters at 2m and 10m depth. Existence of strong ligands that has stability close to EDTA was detected all samples tested. These ligands were also detected by AdCSV using salicylaldoxime as competing ligands. But ligand detected at half wave potential at -1.1 V is not detected or undetectable. It might suggest significance of very stable complexes in water of Lake Biwa.