An automated flow-injection analytical system, equipped with an immobilized L-lysine-a-oxidase reactor (stable for over 6 months) and having a hydrogen peroxide electrode in the manifold, was developed for biosensing L-lysine. A substantial improvement in the selectivity for lysine was achieved by lowering the system temperature to 10°C; the sensor response was linearly dependent on the L-lysine concentration (from tens of µM to mM order). The analytical results were verified by HPLC using protein hydrolyzates as test solutions comprising various interfering amino acids. By the aid of an in-line filter, the leaching of lysine from L-lysine-enriched fish feed into an aqueous buffer was automatically monitored.

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