Spectrophotometric determination of phenols by coupling with diazotized 2,4,6-trimethylaniline in a micellar medium

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Abstract
The unstable absorbances and large values of the blanks obtained when a phenol is determined by coupling with a diazotized arylamine are caused by hydroxy-de-diazoniation of the diazonium ions, followed by coupling of the resulting phenol with the reagent excess in the basic medium. Diazotized 2,4,6-trimethylaniline (TMA) produces 2,4,6-trimethylphenol, which does not couple with the reagent excess, and gives low blanks. A sodium dodecyl sulfate micellar medium is used to prepare the TMA solutions and to catalyse the coupling reaction. The limits of detection were in the range 0.2–4.6 µmol dm–3, with a repeatability of about 2%. The procedure was applied to the determination of epinephrine and paracetamol in pharmaceutical preparations.