AMPEROMETRIC FLOW-INJECTION ANALYSIS OF L-GLUTAMATE USING AN IMMOBILIZED ENZYME REACTOR - AMPLIFICATION BY SUBSTRATE RECYCLING

An amperometric flow injection system with an immobilized enzyme reactor that gives responses amplified by substrate recycling was employed for the highly sensitive determination of L‐glutamate. An L‐glutamate oxidase/glutamic‐pyruvic transaminase coimmobilized reactor was incorporated at fixed positions in a flow system. In the presence of sufficient amounts of L‐alanine and oxygen in the carrier solution, L‐glutamate was repeatedly converted to 2‐oxoglutarate by L‐glutamate oxidase, and the 2‐oxoglutarate produced was subsequently converted back to L‐glutamate by glutamic‐pyruvic transaminase during the passage through the enzyme reactor. As a result of this recycling reaction, a large amount of hydrogen peroxide was produced in the reactor and could be detected amperometrically at a downstream platinum detector. L‐Glutamate was determined with a 20‐ to 30‐fold increase in sensitivity compared to the unamplified responses. The detection limit was 1 pmol of L‐glutamate. Copyright © 1990 VCH Publishers, Inc.