Amperometric flow-injection determination of phenolic compounds at self-assembled monolayer-based tyrosinase biosensors Original Research Article

The performance of a tyrosinase (Tyr) biosensor, constructed by immobilisation of the enzyme by cross-linking atop a 3-mercaptopropionic acid (MPA) self-assembled monolayer (SAM) on a Au disk electrode, is reported for the amperometric detection under flow-injection (FI) conditions of several phenolic compounds (phenol, catechol, m-cresol, p-cresol, 4-chloro-3-methylphenol, 3-chlorophenol, 4-chlorophenol, 2,4-dimethylphenol, 3,4-dimethylphenol, and 2-aminophenol). Experimental variables such as the detection potential (−100 mV versus Ag|AgCl|KCl 3 M), flow rate (1.02 ml min−1), injection volume (350 μl), and pH of the carrier solution (0.05 M phosphate buffer of pH 7.0) were optimised. Under these conditions, the Tyr biosensor exhibited a good reproducibility of the FI measurements, with no need to apply a cleaning or pre-treatment procedure. The useful lifetime of one single biosensor was 5 days. The kinetic parameters of the Tyr reaction were calculated for the 10 phenolic compounds. The analytical performance of the Tyr–MPA–Au electrode under flow through conditions was compared with that of other Tyr electrochemical biosensors reported in the literature. The usefulness of the biosensor for the analysis of real samples was proved by performing the estimation of the content of phenolic compounds in waste waters from a refinery at three different stages in the waste purification process.