COMPARISON OF 2 FIBEROPTIC L-GLUTAMATE BIOSENSORS BASED ON THE DETECTION OF OXYGEN OR CARBON-DIOXIDE, AND THEIR APPLICATION IN COMBINATION WITH FLOW-INJECTION ANALYSIS TO THE DETERMINATION OF GLUTAMATE

A flow-injection system for the fibre-optical determination of L-glutamate in food and pharmaceutical preparations that makes use of two kinds of fibre-optic biosensors is presented. In the first type, an oxygen-sensitive optrode was covered with a membrane onto which was immobilized L-glutamate oxidase. The decrease in oxygen partial pressure in the presence of glutamate as a result of enzymatic reaction was determined via dynamic quenching of the fluorescence of an oxygen-sensitive indicator dye. In the second type, a carbon dioxide-sensitive optrode was covered with a membrane of immobilized L-glutamate decarboxylase. The production of carbon dioxide in the presence of substrate was determined via the changes in the pH of a carbon dioxide sensor consisting of a membrane-covered pH-sensitive fluorescent pH indicator dye entrapped in a hydrogencarbonate buffer. The oxygen optrode-based glutamate biosensor shows a linear response from 0.02 to 1.0 mM glutamate with an relative standard deviation (r.s.d.) of 3% at the 2 mM level (5 measurements). The carbon dioxide optrode-based glutamate biosensor shows a linear response from 0.1 to 2.5 mM glutamate, with an r.s.d. of 3% at the 2.5 mM level (5 measurements). The application of both biosensor optrodes to determinations of L-glutamate in food and pharmaceutical samples is demonstrated. The advantages and disadvantages of both the oxygen and carbon dioxide optrodes are discussed in terms of sensitivity, selectivity and response time.