AN AMPEROMETRIC BIENZYME SENSOR FOR GLYCOLIC ACID DETERMINATION BASEDON SPINACH TISSUE AND FERROCENE-MEDIATION

A new amperometric plant tissue biosensor based on the co-immobilisati on of ground spinach leaves and ferrocene in a carbon paste matrix is described for the determination of glycolic acid. The spinach tissue a cts as a source of glycolate oxidase and peroxidase. Ferrocene is empl oyed as a mediator which facilitates electron transfer between the ele ctrode surface and hydrogen peroxide. The glycolic acid assay is based on the amperometric measurement of a reduction current corresponding to the reduction at the electrode surface of ferricinium ion generated from the enzymatic reaction at 0.00 mV vs. Ag/AgCl. The effect of var ious experimental parameters such as pH, working buffer, applied poten tial and paste composition is explored for optimum analytical performa nce. The bioelectrode exhibits linear response up to 5X10(-4) M glycol ic acid with a relative standard deviation of 1.50% (n = 30) and a det ection limit of 1 x 10(-6) M. The bioelectrode responds rapidly to gly colic acid, with steady state current responses achieved in less than 1 min. The sensitivity of the bioelectrode decreased to 50% of the ori ginal value after 12 days of continuous use.