Coulometric detector cell for use with flow injection

Abstract

A two-electrode cell for constant potential coulometric detection in flow injection systems has been developed. The cell has a saturated calomel electrode with a large surface area and a porous working electrode made of platinum particles. The calomel electrode is not polarised, the potential is kept constant and the electrode serves as both reference and counter electrode. This design of the calomel electrode provides a detector that is simple to construct and easy to use. The cell was tested with the coulometric determination of thallium(I) by means of its oxidation reaction to thallium(III) in a 0.1 M hydrochloric acid medium. A 1.025 V constant potential was applied. Amounts of 0.02–0.17 µequiv. of thallium(I) were determined at flow-rates of 0.2–1.0 ml min^–1, respectively. The detection limit was 8 pequiv. of thallium(I) at a signal to noise ratio of 2:1 and a flow-rate of 1.0 ml min^–1. Amounts between 0.006 and 5.80 µg of thallium(I) were determined by flow injection with a relative standard deviation of 3–6%. A procedure is proposed for calculation of the dispersion in a flow-injection system with coulometric detection.