ASCORBIC-ACID DETERMINATION IN BIOLOGICAL-FLUIDS USING ASCORBATE OXIDASE IMMOBILIZED ON ALKYLAMINE GLASS-BEADS IN A FLOW-INJECTION POTENTIOMETRIC SYSTEM

A flow injection method was developed aimed at the determination of as corbic acid in biological fluids, particularly fruit juices. The enzym e ascorbic oxidoreductase (EC 1.10.3.3), extracted from Cucurbita maxi ma, was immobilized onto alkylamine glass beads using glutaraldehyde a s a bifunctional agent. The ascorbic acid concentration was related to oxygen saturation. Fall in oxygen concentration, as a result of ascor bic acid oxidation, was detected by a low cost, homemade oxygen electr ode. The calibration graph was linear over the range 0.05 to 3.00 mM ( RSD 1%), the maximum number of samples that could be analysed was 90/h . The immobilized enzyme retained its initial activity for 2 mo with m ore than 600 assays.