A novel spectrophotometric determination of trace copper based on charge transfer complex

A new type of colored complex, the charge transfer complex, was used to develop the spectrophotometric determination of copper. The method was based on the formation of a colored product, the charge transfer complex of copper substituted tungstophosphate with 3,3′,5,5′-tetramethybenzidine (TMB), which was stabilized and sensitized by the addition of polyvinyl alcohol (PVA) in aqueous solution. The structure of copper substituted tungstophosphate was Keggin-type according to the results of infrared (IR) spectra. The optimum reaction conditions and other important analytic parameters had been investigated. Beer's law was obeyed in the copper(II) concentration range of 0.003-0.1 μg mL−1, and the molar absorptivity at 660 nm is 2.54×105 L mol−1 cm−1. The proposed method was simple, selective, and sensitive. It was applied to the analytic samples with satisfactory results.