Copper(II)-2,2'-bipyridine-eriochrome cyanine R ternary complex and its application to the spectrophotometric determination of copper(II).

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Copper(II) ion reacted with 2,2′-bipyridine (bpy) and Eriochrome Cyanine R (ECR) to give one of two kinds of ternary complexes according to the amount of reagents in a weakly basic medium. The combining ratios of three components in the complexes were estimated to be Cu(II): bpy: ECR= 1 : 1 : 2 and 1 : 1 : 1, respectively, the former having an absorption maximum at 515 nm and the latter at 550 nm. The color development of the 1 : 1 : 2 complex was utilized in the spectrophotometric determination of copper(II) at microgram level. The ternary complex gave a maximum absorbance at 515 nm in the pH range 10.2–10.6. Under optimum pH, 2,2′-bipyridine and Eriochrome Cyanine R concentrations, a linear relationship holds between the absorbance of the complex and copper(II) concentration up to 6×10−5 mol dm−3. The apparent molar absorption coefficient at 515 nm is about 20400 dm3 mol−1 cm−1, corresponding to Sandell's sensitivity index of 0.0031 μg cm−2.
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