Thallium determination using catalytic redox reaction between methylene blue and ascorbic acid

Methylene blue has been proposed as a new analytical reagent for the catalytic spectrophotometric determination of thallium (I). It reacts with ascorbic acid in acidic medium to form a colorless product. Thallium (I) increases the rate of reaction and it can be determined base on its catalytic effect on the reaction. The reagents and manifold variables influences on the sensitivity were investigated and the optimum conditions were established. The reaction has been followed spectrophotometrically by measuring the decrease in the absorbance of methylene blue at 664 nm. A fixed time method of 180.0 s from initiation of the reaction was used. Under optimum conditions, the proposed method allows the determination of thallium concentrations in the range 3.0 - 200 mu g/mL with a detection limit of 0.09 mu g/mL. This method is free from of most interference. The results of the proposed method for water samples were comparable with atomic absorption spectroscopy and were found to be in good agreement.