Simultaneous determination of the complexing capacity and conditional stability constant of soluble copper(II) complexes in natural-water samples by using a chelate extraction technique

Abstract

Based on a back-extraction of bis(4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedionato)copper(II), a method for the simultaneous determination of the copper(II) complexing capacity of natural water and the conditional stability constant of copper(II) complex with naturally occurring ligands was developed. The feasibility of the proposed method was confirmed using nitrilotriacetic acid and ethylenediamine-N,N'-dipropionic acid instead of naturally occurring ligands. It was then applied to a pond-water sample. The results indicated that two types of copper(II) complexes having different stabilities were formed upon the addition of copper(II) to the sample. By using the copper(II) complexing capacity and the conditional stability constant, the distribution of copper(II) species in pond water was calculated. It was found that most of the copper(II) in pond water exists as a complex with a naturally occurring ligand, and that the concentration of free copper(II) ion is extremely low.