Analytical Sciences

Evaluation of the Copper(II) Complexing Ability of Ultrafiltered Humic Acid by the Solvent Extraction Method

Hideyuki ITABASHI, Yusuke KAMATA, Daisuke KAWAGUCHI, and Hiroshi KAWAMOTO

Department of Applied Chemistry, Faculty of Engineering, Gunma University, Kiryu, Gunma 376-8515, Japan

A commercial humic acid dissolved in water was fractionated to nine samples by means of ultrafiltration (UF); the nominal molecular weight used for UF membranes was 1 k - 200 kDa. Concerning the nine samples, copper(II) complexing capacities (CuCC) and conditional stability constants (beta) of the formed copper(II) complexes were measured by a solvent extraction method. A total organic carbon (TOC) and the UV-VIS absorption ratio (E_{350 nm}/E_{450 nm}) were also measured. From a comparison of these data, it was found that a) humic acids in each fraction formed two kinds of copper(II) complexes with different stability; b) the beta values obtained from each fraction were almost the same; c) large CuCC values were observed in the molecular weight range from 10 kDa to 20 kDa and below 1 kDa; d) molecules with molecular weight higher than 50 kDa scarcely had any copper(II) complexing ability; e) the values of CuCC/TOC of each fraction were in the range from 1.7 to 3.4 x 10^-7 mol mg^-1.

J-STAGE: View this article in J-STAGE