Enzymatic sensor coupled to a flow-injection analysis system for the determination of salicylate

A quick and reliable enzymatic method for the direct determination of salicylate in pharmaceuticals after appropriate dilution is described. The enzyme salicylate hydroxylase was attached directly onto a platinum working electrode of a wall-jet cell coupled with a flow-injection analysis system. Therefore, the platinum electrode was oxidized, silanized and derivatized with p-tetrachloroquinone, then the enzyme was covalently bound to the quinone and afterwards crosslinked with glutardialdehyde. The enzymatic conversion of salicylate to the electrochemically detectable catechol is about 25%. It can mainly be influenced by the amount of coenzyme added and by the flow velocity. The response of the biosensor is linearly proportional to the concentration of salicylate between 7.25 μ M and 4.35 mM. A high sample throughput (60 h−1) is possible, and the biosensor is stable for at least three months. The assayed samples yielded relative standard deviations between 1.7 and 4.3% and recoveries between 83 and 104%.