Self-indicating flow visible spectrophotometric titrations in a variable-volume tank reactor

Abstract

Spectrophotometric titrations were carried out in an emptying tank stirred reactor, in which linear concentration gradients were produced. These gradients were utilized to titrate the analyte within the tank by means of a titrant delivered by pump flow: spectrophotometric detection was made in the exit stream. Self-indicating titrations, in which changes in the absorbance of the analyte, titrant or reaction product were monitored, were performed and found to conform to the theoretical prediction. Owing to the external detection system employed, dispersion and transportation lag effects were observed, and these were accounted for theoretically. The precision of the titrations was affected by the precision of the flow rates employed. The relative errors were between 1 and 2% using peristaltic pumps. The titrations studied were iron(III) salicylate with ethylenediaminetetraacetic acid, iron(II) with permanganate, iron(III) with thiocyanate, and 2,4-dinitrophenol with hydroxyl. These linear concentration gradient titrations, in which the absorbance of the product is monitored, fulfil the conditions of the continuous variations or Job's method for determining the stoichiometry of complexes, and are a means of automating the procedure.