Spectrophotometric titration of some thiazine dyes with iron(II) in buffer medium in the presence of oxalate

Abstract

An accurate and convenient spectrophotometric titration method was developed for the determination of microgram amounts of seven thiazine dyes employing iron(II) as a reductant in buffer medium (optimum pH 3.7–4.7) in the presence of sodium oxalate (optimum concentration 0.06–0.12 mol l^–1). All the dyes are rapidly and quantitatively reduced to their colourless leuco-bases in a two-electron reduction with iron(II). The redox potentials of the iron(III)–iron(II) couple in buffer media of different pH and oxalate ion concentrations were measured. The function of pH and oxalate ion in the reaction medium is discussed.