Acridine orange and chlorite reaction — An indicator reaction for the trace determination of Ru(III)

Abstract

Catalysis by transition metal ions plays an important role in understanding the mechanistic aspects of a particular redox reaction. Ru(III) acts as an efficient and potential catalyst in many redox reactions. Hence the use of Ru(III) chloride as a homogeneous catalyst in acidic medium is of present interest. Based on the highly selective catalytic efficiency of Ru(III) on the oxidation of acridine orange {3,6-bis (dimethylamino) acridine zinc chloride double salt}(AO⁺) by acidic chlorite, a fixed-time kinetic analytical procedure for determination of Ru(III) is developed. The lowest determination limit attainable with the developed method is 1.01 ng/mL. The method allows determination of Ru(III) with no interference from a wide range of cations. Tolerance ratios have also been computed. With excess concentration of reactants, both un-catalyzed and catalyzed reactions follow a pseudo-first order kinetics in [AO⁺], fractional order kinetics in oxidant and first order kinetics in catalyst [Ru(III)]. The rate coefficient of the un-catalyzed reaction is 4.45<img src='/image/spc_char/cross.gif' border=0>10^-4s^-1 while the catalytic constant for the catalyzed reaction is 8.00<img src='/image/spc_char/cross.gif' border=0>10^-4s^-1. Retarding effect of increasing ionic strength suggests the involvement of oppositely charged species in rate determining step. A tentative mechanism has also been proposed based on the results of variation of various factors.