Colorimetric Determination of Stability Constant of Acetaminophen-Cu(II) complex by Classical Equation Depending on Stoichiometric Curves

Abstract

Acetaminophen is a nonsteroidal anti-inflammatory drug (NSAID) that is used for the treatment of pain, fever and headache. Classical equation has been used in the calculation of stability constant of acetaminophen-Cu(II) complex depending on the theoretical explanation of the stoichiometry, continuous variation and mole ratio methods.The formation of Cu(II) complex with acetaminophen was studied colorimetrically at an absorption maximum of 630 nm at 25 and 40 ^oC. The data showed that Cu(II) and acetaminophen combine in the molar ratio of 1:1  at pH 7.4 with ionic strength maintained using 0.1M KNO₃. Calculated stability constants values were 1.18 x 10² and 1.11 x 10² using continuous variation method and 1.25 x 10² and 1.11 x 10² using mole ratio methods at 25 and 40 ^oC respectively. Calculated ∆G^Ɵ for the complex were - 1.18 x 10⁴ and-1.23 x 10⁴ J using continuous variation method and - 1.20 x 10⁴ J and -1.23 x 10⁴ J using mole ratio method at 25 and 40 ^oC respectively. The stoichiometry, stability constant and Gibbs free energy results suggested that acetaminophen used in the study is a good chelating agent and can be an efficient antidote in the therapy of Cu(II) overload or poisoning