Catalytic spectrophotometry for the determination of manganese at trace levels by a novel indicator reaction
A new kinetic spectrophotometric method is developed for the measurement of Mn(II) in natural water samples. The method is based on the catalytic effect of Mn(II) with the oxidation of Gallocyanin by KIO4 using nitrilotriacetic acid (NTA) as an activation reagent at 620 nm. The optimum conditions obtained are 4.00 × 10-5 M Gallocyanin, 1.00 × 10-4 M KIO4, 1.00 × 10-4 M NTA, 0.1 M HAc/NaAc buffer of pH = 3.50, the reaction time of 5 min and the temperature of 30 °C. Under the optimum conditions, the proposed method allows the measurement of Mn(II) in a range of 0.1-4.0 ng mL-1 and with a detection limit of down to 0.025 ng mL-1. The recovery efficiency in measuring the standard Mn(II) solution is in a range of 98.5-102%, and the RSD is in a range of 0.76-1.25%. The newly developed kinetic method has been successfully applied to the measurement of Mn(II) in both some environmental water samples and certified standard reference river water sample, JAC-0031 with satisfying results. Moreover, few cations and anions interfere with the measurement of Mn(II). Compared with the other catalytic-kinetic methods and instrumental methods, the proposed kinetic method shows fairly good selectivity and sensitivity, low cost, cheapness, low detection limit and rapidity. It can easily and successfully be applied to the real water samples with relatively low salt content and complex matrices such as bottled drinking water, cold and hot spring waters, lake water, river water samples.