Bromopyrogallol Red: A New Microanalytical Reagent for Amperometric Estimation of Dy(III) and Gd(III)†

Abstract

Bromopyrogallol Red (BPR) has been extensively used as an indicator
but its electro-reducibility has proved it to be a very useful amperometric
reagent. BPR reduces on a DME in KNO₃ in the entire pH range 2.4 to
9.5. It produces single stage reduction wave below pH 4, but a two stage
reduction wave in the basic range. Progressive ionization of hydroxyl group
and distinct colour species of BPR, have also been studied using a Bausch
and Lomb spectronic-20 spectrophotometer in order to support
electroanalytical studies. On performing amperometric titrations of Dy(III)
and Gd(III) with BPR at its plateau potential 1.0 V at pH 2.6 and
μ= 0.4, reversed L-shaped titration curves have been observed indicating
metal to BPR ratio 1 : 1 and the colour changes from claret red to orange
yellow. The reagents have been tested in presence of various diverse ions
and tolerance limits have been computed. Na⁺, K⁺, Li⁺, Cl^-, ClO₄^-,
CH₃COO^-, Pd²⁺, Fe³⁺ ions did not interfere in the titrimetric Rrocedure.
However, small amounts of Bi³⁺, Pb²⁺, Ni²⁺, CO²⁺, Cd²⁺, Mg²⁺ and rare
earth metals have hampered the titrimetric estimations.