Semi-automated kinetic determination of phenolic compounds using a fluoride-selective electrode and based on their micellar-catalysed reaction with 1-fluoro-2,4-dinitrobenzene
A kinetic-potentiometric method is described for the determination of phenol and phenolic drugs based on monitoring their reaction with 1-fluoro-2,4-dinitrobenzene, catalysed by cetyltrimethylammonium bromide micelles, using a fluoride-selective electrode. The measurement step was automated by interfacing a digital electrometer to a microcomputer. By measuring the initial slopes (ΔE/Δt), kinetic parameters (reaction order and rate constants) were obtained and kinetic determinations in the range 6 × 10–6–7 × 10–4M were performed for phenol, acetaminophen, isoxsuprine, nylidrin, isoproterenol and metaraminol. Micellar catalysis was found to enhance the reaction rate of the various phenolic compounds tested by between 37 and 290 times. The proposed method did not suffer any interference from excipients or from cloudy and coloured solutions and was evaluated by assaying acetaminophen in commercial formulations. The results showed good agreement with those obtained using established methods.