Amperometric determination of p-hydroxybenzoic acid esters using an oxygen electrode

An enzyme method for the determination of p-hydroxybenzoic acid esters is described based on the indirect electrochemical monitoring of p-hydroxybenzoic acid via its reaction with oxygen in the presence of p-hydroxybenzoate hydroxylase. Derivative amperometric signals due to oxygen depletion enable a one-point kinetic analysis to be carried out. Esterase hydrolyses p-hydroxybenzoic acid esters to the free acid and p-hydroxybenzoate hydroxylase catalyses the reaction of p-hydroxybenzoic acid with NADPH to produce NADP+, which is accompanied by a stoicheiometric consumption of oxygen. The method has been successfully applied to the analysis of real soft drink samples.