Development of amperometric biosensors for the determination of glycolic acid in real samples.

The first enzyme-based biosensors capable of determining glycolic acid in various complex matrixes, such as cosmetics, instant coffee, and urine, are presented in this paper. Two separate designs, both based on a three-membrane configuration consisting of an inner cellulose acetate membrane (CA) and an outer polycarbonate membrane (PC), which sandwich a membrane bearing the biomolecule(s), are proposed. Glycolate oxidase was immobilized onto a modified polyethersulfonate membrane by means of chemical bonding, and glycolate oxidase/catalase enzyme mixture was immobilized into a mixed-ester cellulose acetate membrane through physical adsorption. The membrane assemblies were mounted on an amperometric flow cell (hydrogen peroxide detection at a platinum anode poised at +0.65 V vs Ag/AgCl/3 KCl) or on an oxygen electrode, respectively. Both configurations were optimized with respect to various working parameters. The proposed biosensors are interference-free to common electroactive species and were successfully applied for the determination of glycolic acid in various samples, showing an excellent agreement with a reference photometric method. The validity of the proposed method in samples, in which the reference method was not applicable, was tested with recovery studies. Values of 102 +/- % were obtained. Inherent interference of oxalic acid was manipulated by using a primary amine-containing buffer and the enzyme catalase. Both systems were designed in order to be compatible with the current technology of the most widely used commercial analyzers.