Kinetic-fluorimetric determination of copper(II), based on its catalytic effect on the oxidation of morin with hydrogen peroxide
Abstract
A kinetic method is described for the determination of trace amounts of copper(II) based on its catalytic effect on the oxidation of 3,5,7,2′,4′-pentahydroxyflavone (morin) by hydrogen peroxide. The reaction is followed by measuring the rate of decrease in fluorescence (λex.= 463 nm, λem.= 548 nm). The optimum conditions are as follows: pH 10.5 (ammonium chloride-ammonia buffer), 0.005% morin, 20% ethanol, 0.9% hydrogen peroxide and 25 °C. The calibration is linear for concentrations up to 50 ng ml–1 with a precision of 1.7% and the detection limit is 0.4 ng ml–1 of Cu(II). The main interferences are due to Be(II), Mn(II), Zr(IV), Fe(III) and Mn(VII).
In the absence of H2O2, higher amounts of Cu(II) catalyse the air oxidation of morin. In this instance, the calibration graph is linear between 150 and 500 ng ml–1.