Simultaneous spectrophotometric determination of o-cresol and m-cresol in urine by use of the kinetic wavelength-pair method

Abstract

The kinetic wavelength-pair method was applied to the simultaneous determination of o-cresol and m-cresol, based on their oxidative coupling with aniline in the presence of hypochlorite as oxidant and nitroprusside as catalyst. The benzoquinoneanils produced exhibited severe spectral overlap. Resolution of this isomer mixture by using discrete wavelengths was subject to a high degree of error for the determination of m-cresol since the ratios v_o-cresol/v_m-cresol(where v denotes initial rate for the oxidative coupling reaction) and ε_o-cresol/ε_m-cresol(where ε is the absorptivity of reaction products) were greater than unity at any given wavelength. Selectivity in the resolution was achieved by measuring the initial rate difference at the wavelength pair 666–566 nm where the contribution of o-cresol was removed. o-Cresol and m-cresol were simultaneously determined at mass ratios between 5 : 1 and 1 : 5 at concentrations from 1 to 5 µg ml^–1, with relative standard deviations of less than 3%. The proposed method was applied to the determination of o-cresol and m-cresol in urine samples, with analytical recoveries ranging between 95 and 105%.