Coulometric microflow titrations with chemiluminescent and amperometric detection of the equivalence points — basic investigations and bromimetric titration of low concentration solutions of arsenite

Abstract

Coulometric flow titrations were combined with chemiluminescent detection of the equivalence points. The flow channel system consists of a miniaturized flow electrolytic cell, a knotted type tubular reactor and a capillary wall-jet chemiluminescence detector with an outer tube for the addition of luminol reagent solution. The chemiluminescence detector can be used to determine bromine in the range between 0.1 μM and 1 mM opening up a sensitive way to follow flow titrations with linear concentration gradients of bromine. Very low concentrations of arsenite can be titrated in a sample flow channel system with electrogenerated bromine. The chemiluminescence detection was compared with the amperometric monitoring of the titration curves. To perform such gradient controlled flow titrations without calibration, it was necessary to minimize the so-called tailing. At gradient generation times ≥120 s, arsenite can be titrated almost without calibration in the range between 0.05 and 100 μM. The accessible determination range is determined by the maximum electrolysis current and the sample flow rate. Added micromolar concentrations of arsenite were accurately determined in river water and phosphate solutions.