SIMULTANEOUS SPECTROPHOTOMETRIC DETERMINATION OF O-CRESOL AND M-CRESOL IN URINE BY USE OF THE KINETIC WAVELENGTH-PAIR METHOD

The kinetic wavelength-pair method was applied to the simultaneous det ermination of o-cresol and m-cresol, based on their oxidative coupling with aniline in the presence of hypochlorite as oxidant and nitroprus side as catalyst. The benzoquinoneanils produced exhibited severe spec tral overlap. Resolution of this isomer mixture by using discrete wave lengths was subject to a high degree of error for the determination of m-cresol since the ratios nu(o-cresol)/nu(m-cresol) (where nu denotes initial rate for the oxidative coupling reaction) and epsilon(o-creso l)/epsilon(m-cresol) (where epsilon is the absorptivity of reaction pr oducts) were greater than unity at any given wavelength, Selectivity i n 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 m ass ratios between 5:1 and 1:5 at concentrations from 1 to 5 mu g ml(- 1), with relative standard deviations of less than 3%, The proposed me thod was applied to the determination of o-cresol and m-cresol in urin e samples, with analytical recoveries ranging between 95 and 105%.