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 Ho <–4.75 (where Ho 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 R2– 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) pKa1. 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.