Flow monitoring of glutamate and aspartate in foods and pharmaceutical products with immobilized bienzyme electrochemical cells

Electrochemical enzyme cells for glutamate and aspartate analysis have been assembled and used in continous-flow and in flow-injection analysis. The enzymes, glutamate oxidase (GOD) and aspartate amino-transferase (AST), were co-immobilized on an Immobilon Immuno-affinity membrane, which was placed into a three-electrode, flow-through cell. Additional protective membranes were used to reduce the electrochemical interferences and to protect the immobilized enzymes. Thin-layer and walljet cells were used and compared. Calibration curves for glutamate and aspartate showed a linearity range of 1–500 μmol/L and 10–500 μmol/L respectively. The sensitivity was higher using the flow-through system with a response time of 2 min. Better reproducibility was achieved using the FIA procedure with a response time of less than 1 min. Glutamate in foodstuffs and asparatate in some pharmaceutical products were analyzed. Results were compared and correlated well with an HPLC procedure.