Spectrophotometric and spectrofluorimetric study of Rose Bengal B and its reaction with platinum(IV)

Abstract

Aqueous solutions of Rose Bengal B contain four ionic species: H₃R⁺ at H_o <–4.75 (where H_o is the Hammet acidity function for strongly acidic solutions); H₂R at H₀>–4.75, pH <3.6; HR^– at 3.51 < pH <4.05; and R^2– at pH >4.05. The pK for these equilibria in the pH zone are pK₁= 3.51 and pK₂= 4.05 and in the acid function (Hammet function) pK_a1. Polymeric species and excimers have been found in the ground and in first excited state, respectively, at concentrations higher than 10^–4M. Pt(IV) reacts with Rose Bengal B giving a colourless solution that does not show any fluorescence. Platinum(IV) has been determined fluorimetrically at concentrations higher than 0.2 p.p.m. The other noble metals do not interfere.