A catalytic detection system based on the use of immobilized tyrosinase and two different transducers (photometric and electrochemical) is described. Comparison between tyrosinase immobilized in a packed-bed reactor and at the surface of a graphite electrode is discussed in terms of sensitivity in a flow injection system. The enzyme electrode configuration gives the highest sensitivity for the quantitation of dopamine. For the immobilized tyrosinase reactor with photometric detection the range for dopamine is linear up to 0.75 mM (136 micrograms ml-1) and the immobilized tyrosinase reactor with electrochemical detection and the tyrosinase electrode extends this dynamic range to 1 mM (181 micrograms ml-1). Liquid chromatographic separation and post-column detection using the tyrosinase electrode is shown for spiked samples of serum.
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