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Visual Discrimination of Phenolic Group β2-Agonists and the Ultrasensitive Identification of Their Oxidation Products by Use of a Tyrosinase-Based Catalytic Reaction

Xiong, Huayu, Guo, Chunhui, Liu, Ping, Xu, Wei, Zhang, Xiuhua, Wang, Shengfu
Analytical chemistry 2014 v.86 no.10 pp. 4729-4738
absorbance, aniline, benzene, blood, color, colorimetry, electrochemistry, isoxsuprine, mass spectrometry, oxidation, pH, phenol, ractopamine, reaction mechanisms, resorcinol, screening, urine
The fast, visual discrimination of β₂-agonist drugs is needed for the on-site screening of various types of β₂-agonists in blood and urine samples. We developed a simple, rapid, one-step colorimetric method to detect phenolic β₂-agonists by use of a tyrosinase catalytic reaction, which involved the oxidation of the phenol group on the benzene rings of β₂-agonists. The enzymatic oxidation products of β₂-agonists with phenolic groups exhibited different color transitions based on the different substituent groups on the aromatic ring, whereas β₂-agonists with the aniline group or the resorcinol group remained colorless. This visual color discrepancy has been used to intuitively and conveniently differentiate the phenolic group β₂-agonists, such as ractopamine, isoxsuprine, ritodrine, and fenoterol. The oxidation products of these compounds have been identified using mass spectrometry, and the possible reaction mechanisms between β₂-agonists and tyrosinase have been deduced. The parameters that govern the analytical performance of the reaction product, including the pH of the buffer solution, the concentration of tyrosinase, and the incubation time, have been studied and optimized using ultraviolet–visible (UV–vis) spectroscopy and electrochemical methods. Under the optimal experimental conditions, the absorbance intensity and electrochemical signal were found to increase proportionally to the concentrations of the phenolic group β₂-agonists, which gave a quantitative description of the β₂-agonists in solution.