Catalytic effect of some inorganic ligands on a ligand substitution reaction involving mercury(II) and its application as a differential kinetic method of analysis

To design a sensitive and selective kinetic method for determining a catalyst, the kinetics of the ligand substitution reaction between the mercury(II)-4-(2-pyridylazo)resorcinol complex and 1,2-cyclohexanediamine-N,N,N',N'-tetraacetic acid together with the catalytic effect of some inorganic ligands on this reaction were studied. The rate constant for a catalyzed reaction path was found to be linearly correlated with the electron donor constant of the catalyst. From this correlation, the difference in reactivity between sulfite or thiosulfate and sulfate was established. Under the selected conditions, sulfite up to 1.5 x 10(-6) M and thiosulfate up to 7 x 10(-7) M could be determined with detection limits of 3 x 10(-8) and 2 x 10(-8) M in the presence of 10 000 and 25 000-fold molar amounts of sulfate, respectively. The tolerance level in the determination of 1 x 10(-6) M of sulfite and 4 x 10(-7) M of thiosulfate was studied for 15 inorganic anions and 44 metal ions.