Photochemical redox titrations with tungsten(V)

A titration method has been developed for the determination of micromolar quantities of dichromate, vanadate and hexacyanoferrate(III) with in situ photochemical generation of tungsten(V) as the titrant. Precision of 1–3% was obtained. Spectrophotometric end-points were utilized because of the intense blue color of the titrant (λ_max 770nm; _max7.10³). Because the titrant reacts with oxygen, a closed, argon-flushed, circulating photolysis apparatus was constructed. Optimal solution condi- tions were investigated ; tungsten reagent must be added as the solid just before titra-tion. An induced reaction between dichromate and glucose was found, but satisfactory linear calibration curves were obtained. With reduced photolytic intensity, 0.2 μeq of dichromate can be determined.