Amperometric enzyme electrodes for the determination of l-glutamate

Electrodes for amperometric measurement of l-glutamate were prepared by immobilization of l-glutamate oxidase on an Immobilon-AV Affinity membrane and attachment to an oxygen/hydrogen peroxide sensor. The response of the hydrogen peroxide sensor was linear over the concentration range 5.0 x 10(-8)-5.0 x 10(-4)Ml-glutamate, with a limit of detection of 35nM. Attachment of a size-exclusion membrane (cut-off for molecular weight > 100) or of a hydrophobic oxygen membrane eliminated electro-oxidizable interferences, but the response was attenuated by a factor of 2-3. The response may be amplified 10-fold by co-immobilizing l-glutamate dehydrogenase with the l-glutamate oxidase. The electrode initially lost 25% of its activity but was then stable for more than 320 days and at least 200 assays. The electrode was successfully used to assay glutamate in a protein tablet and in several food products. A flow-injection system was assembled for the continuous assay of l-glutamate.