Spectrophotometric investigation of the complexing reaction between rutin and titanyloxalate anion in 50% ethanol

Abstract

In the present work, rutin (3,3',4',5,7-pentahydrohyflavone-3-rhamnoglucoside) was determinated via a complexing reaction with a titanyloxalate anion. K-2[TiO(C2O4)(2)] and rutin react in 50% ethanol forming a 1:2 complex in a pH range from 4.00 to 11.50, in which the TiO(C2O4)(2)(2-) ion is linked to rutin through the 4-carbonyl and 5-hydroxyl group. The thermodynamic stability constant log beta(2)(0) of the complex is determined to 10.80 at pH = 6.50. The change of the standard Gibbs free energy Delta G(0) amounts to -61 kJ . mol(-1), indicating that the process of complex formation is spontaneous. The optimal conditions for the spectrophotometric determination of microconcentrations of rutin are at pH = 6.40 and lambda = 430 nm, where the complex shows an absorption maximum with a molar absorption coefficient a(430) = (60+/-2) . 10(3) dm(3) . mol(-1) . cm(-1). The method is applied rutin determination from tablets.