Spectrophotometric study on the reactions of iron(II) and iron(III) with Bromopyrogallol Red and hexadecyltrimethylammonium bromide

Abstract

Bromopyrogallol Red (BPR) combines with iron(III) in the presence of hexadecyltrimethylammonium bromide (CTMAB) to form an intensely blue complex having a molar absorptivity of 5.20 × 10 4l. mole −1.cm −1 at 635 nm. The complex contains three molecules of BPR co-ordinated to an iron(III) ion, and two molecules of CTMAB associated with each BPR molecule, giving the overall formula (CTMAB) 6(BPR) 3Fe(III). Iron(II) also reacts with BPR and CTMAB in the presence of dissolved oxygen to form the iron(III) complex. No oxidizing or reducing agents are required for the determination of total iron in mixtures of iron(III) and iron(II), and Beer's law is followed from 0.05 to 0.5 ppm iron (1.00-cm cells). Of nine metal ions tested at the 1-ppm level, only manganese(II) and vanadium(V) interfere. Copper(II), cobalt(II), zinc, lead, nickel, aluminium and chromium(III) produce little or no interference when present at 100 ppm concentration.