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 (λ_ex.= 463 nm, λ_em.= 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.