Titrimetric methods for the determination of sulphonphthalein dyes

Abstract

Simple methods are described for the determination of sulphonphthalein dyes, based on titration procedures with electrometric end-point detection. In the first method, titrations of sulphonphthaleins in the form of univalent anions were monitored potentiometrically with a PVC membrane coated-wire electrode. The value of the potentiometric titration break depended on the substituents of the dye and could be correlated with Charton's steric parameters, which permited the titratability of the dyes as a function of their structure to be predicted. For the dyes that were not titratable on the basis of ion-pair formation, a second method is recommended, based on bromination followed by iodimetric titration with sodium thiosulphate using biamperometric end-point detection. Both methods were simple and rapid and the results were satisfactory.