Kinetic-fluorimetric study of the activator effect of zirconium(IV) on the air oxidation of morin catalysed by manganese(II)

Abstract

A kinetic study of the activator effect of zirconium(IV) on the manganese(II)-catalysed air oxidation of morin has been made. The effect of ammonia, ethanol, morin, manganese(II) and zirconium(IV) concentrations and of temperature was examined in order to obtain the optimum conditions for the determination of zirconium(IV) and to establish the kinetic dependence of each of these variables for the catalysed and activated reactions. The reaction was followed by measuring the decrease in fluorescence at 548 nm, with an excitation wavelength of 417 nm. A kinetic-fluorimetric method for the determination of zirconium(IV) is proposed. The calibration graphs were obtained by applying the fixed time, fixed concentration, initial rate and rate constant methods. The method is linear up to 250 ng ml^–1 of zirconium(IV). The precision was calculated for the different methods applied and was always smaller than 3%. The main interferences were due to Be^II, Cu^II and Mg^II. Moreover, the zirconium(IV)'s activator effect has been used to improve the kinetic-fluorimetric determination of manganese(II). The method is linear up to 60 ng ml^–1, with a detection limit of 0.26 ng ml^–1 for manganese(II), and a sensitivity enhancement of about 50% is obtained in the presence of the activator.