Determination of trace amounts of mercury(II) in water samples using a novel kinetic catalytic ligand substitution reaction of hexacyanoruthenate(II)

A simple, sensitive, selective and rapid kinetic catalytic method has been developed for the determination of Hg(II) ions at micro-level. This method is based on the catalytic effect of Hg(II) ion on the rate of substitution of cyanide in hexacyanoruthenate(II) with nitroso-R-salt (NRS) in aqueous medium and provides good accuracy and precision. The concentration of Hg(II) catalyst varied from 4.0 to 10.0 × 10⁻⁶ M and the progress of reaction was followed spectrophotometrically at 525 nm (λ_max of purple-red complex Ru(CN)₅NRS]³⁻,  = 3.1 × 10³ M⁻¹ s⁻¹) under the optimized reaction conditions; 8.75 × 10⁻⁵ M Ru(CN)₆⁴⁻], 3.50 × 10⁻⁴ M nitroso-R-salt], pH 7.00 ± 0.02, ionic strength, I = 0.1 M (KCl), temp 45.0 ± 0.1 °C. The linear calibration curves, i.e. calibration equations between the absorbance at fixed times (t = 15, 20 and 25 min) versus concentration of Hg(II) ions were established under the optimized experimental conditions. The detection limit was found to be 1.0 × 10⁻⁷ M of Hg(II). The effect of various foreign ions on the proposed method has also been studied and discussed. The method has been applied to the determination of mercury(II) in aqueous solutions.