Spectrophotometric Determination of Copper(II) with 4-(2-Pyridylazo)-resorcinol Disodium in Pharmaceuticals

Abstract

Spectrophotometric determination of copper(II) with 4-(2-pyridylazo)- resorcinol disodium salt dihydrate (PAR) in aqueous phosphate buffer at pH = 10 was studied. It was suggested in this study that two complexes are formed. The first is Cu(PAR) with absorption maxima at 510 nm, ε = 4.0 × 10⁴ mol^-1 cm^-1 L and the second is Cu(PAR)₂ with absorption maxima in the range 495-500 nm, ε = 7.62 × 10⁴ and 7.12 × 10⁴ mol^-1 cm^-1 L in absence and presence EDTA respectively. The formation constant pK for the Cu(PAR)₂ complex is in order of 10¹². Beer's law is obeyed for Cu-PAR complex, ratio of 1:2, on the range of 1 × 10^-6-2.5 × 10^-5 M and 0.1 × 10^-6-2.5 × 10^-5 M with relative standard deviation 1.7 and 2.2 % in absence and presence of EDTA respectively. Cr³⁺, As³⁺, Ni²⁺, Co²⁺, Fe³⁺ and Pb²⁺ do not cause any considerable interference. Whereas, Hg²⁺, Zn²⁺ and Cd²⁺ do not interfere in presence of EDTA. This method was also applied successfully for determination of copper(II) in some pharmaceuticals in the presence of EDTA. The relative standard deviation did not exceed ± 1.5 %.