Kinetic-Catalytic and Spectrophotometric Determination of Hg(II) Using its Catalytic Effect on Ligand Substitution Reaction between Hexacyanoferrate(II) and Pyrazine

A sensitive, simple and rapid spectrophotometric method for the determination of mercury (II) based on its catalytic effect on the abstraction of coordinated cyanide from hexacyanoferrate (II) by pyrazine has been developed using fixed time procedure. The extent of the reaction is monitored spectrophotometrically by measuring the increase in absorbance at λ_max=440 nm of the yellow colored complex, [Fe(CN)₅Pz]³⁻ under the reaction conditions; [Fe(CN)₆]⁴⁻=7.2×10⁻³ mol L⁻¹, [P_z]=3.75×10⁻⁴ mol L⁻¹, temperature=25.0±0.1 °C, pH= 2.50±0.02 and I=0.1 mol L⁻¹(KNO₃). The experimental rate data under the conditions used in the present study exhibited a linear dependence between absorbance and [Hg²⁺] catalyst in the range 5.065–50.15 ng mL⁻¹. The detection limit is found to be 4.01 ng mL⁻¹. The maximum relative standard deviations and percentage errors for mercury(II) determination are found to be 2.2 and 3 % respectively. The percentage recoveries are found to be in the range of 99–102 %. Analytical data fordetermination of mercury(II) is presented together with the application of proposed method in water spiked synthetic mixtures. The validity of the proposed method is tested by comparing the results obtained by present method with atomic absorption spectrometry.