Simultaneous determination of hydroquinone ethers in cosmetics after preconcentration at a carbon paste electrode

Abstract

A simple electroanalytical method for the simultaneous determination of hydroquinone ethers has been developed using a carbon paste electrode. Hydroquinone (HQ), hydroquinone monobenzyl ether (MBHQ) and hydroquinone dimethyl ether (DMHQ) can be preconcentrated at the electrode surface prior to voltammetric determination. For differential pulse voltammetric measurements with suitable methodical parameters, linear concentrations are found over the ranges 0.07–8.8 mg l^–1, 0.13–31.4 mg l^–1 and 0.15–33 mg l^–1 for HQ, MBHQ and DMHQ, respectively. A comparison is made between the detection limit of platinium, glassy carbon and carbon paste electrodes. The method is applicable to the quantitative determination of hydroquinone ethers in skin lighteners and bleaching creams. The depigmenting agents of bleaching cream in 0.1 mol l^–1 phosphate buffer (pH 2.1) have a stripping peak at +0.220, +0.448 and +0.780 V for HQ, MBHQ and DMHQ, respectively. Comparison with results obtained from capillary gas chromatography shows good agreement, to within, on average 2.7%.