IMMOBILIZATION OF GLUTAMATE OXIDASE ON NONPOROUS GLASS-BEADS - AUTOMATED FLOW-INJECTION SYSTEM FOR THE ASSAY OF GLUTAMIC-ACID IN FOOD SAMPLES AND PHARMACEUTICALS

An enzymic method is proposed for the determination of glutamic acid i n food samples and pharmaceuticals. The method is useful in the range 0.01-0.5 mmol 1-1, with a detection limit of 0.005 mmol l-1 for an inj ection volume of 52 mul. L-Glutamate oxidase from Streptomyces sp. X-1 19-6 was immobilized on non-porous glass beads, and the H2O2 produced was caused to react with Trinder's reagent. Various parameters were s tudied for the establishment of the optimum operating conditions for a n in-house flow injection manifold with a spectrophotometric detector. Many interfering species and several amino acids were tested in order to verify the specificity of the enzyme reactor. Experimental data fo r interfering organic and inorganic substances are reported. The syste m works very selectively for glutamic acid and glutamates. The method is ideally suited to the assay of glutamates in a large number of samp les within a single working day, as the frequency is 40 samples h-1. T he relative standard deviation is 1.8% for six assays. The immobilized reactor is stable for a long period under proper conditions of storag e. The accuracy of the proposed method was tested by comparison of the results with those of the Association of Official Analytical Chemist' s method and with the manufacturer's specifications for the analysed s amples, where available. Good agreement was obtained. Recovery studies yielded results between 97 and 105%.