A method for the analysis of intermediates of oxidative hair dyes in cosmetic products

A method has been developed and validated for the analysis of some commonly used intermediates of oxidative hair dyes: phenylenediamines, toluenediamines, aminophenols, l-naphthol, resorcinol, and hydroquinone. The target analytes are ion-paired prior to HPLC analysis with gradient elution employing phosphate buffer-acetonitrile as mobile phase and detection in the wavelength range 220-400 nm by a photodiode array detector. A spectral-library, consisting of 220-400 nm spectra of the target substances and their HPLC retention times, has been prepared for the identification. A method of sample preparation was established and applied to the analysis of a series of cosmetic formulations for hair dyeing. The method has been found to be suitable for routine analysis of the target intermediates of oxidative hair dyes, and it may also be suitable for the analysis of some non-target intermediates of these substances.