Estudo de métodos para determinação de hidroquinona em formulações farmacêuticas

Abstract

Hydroquinone is a phenolic compound used as a reference substance in pharmaceuticals designed for treatments of dyschromias induced by hyperpigmentation processes. Dermatological diseases of this segment are very ordinary and appear among the main causes of the medical advice demand, according to recent data published by the Brazilian Society of Dermatology. In Brazil, hydroquinone is found in some skin-bleaching formulations with up to 4% concentration, however, despite of being widely used, some authors have been published papers warning about the adverse effects caused by its long-term use. One of the criteria considered is the molecule stability, since the hydroquinone easily undergoes oxidation and its product, benzoquinone, could be associated with genotoxic mechanisms. Therefore, the dosage of these drugs is important to guarantee their quality, safety and efficacy. Thus, the aim of this work was to develop an investigative study to enlighten the chemical stability of hydroquinone in those products, as well as the development of an analytical quantitative methodology. Over the experimental procedure, spectroscopic, electroanalytical and electromigration techniques were explored. Once stablished the standard materials acquired for this work are within the purity certification parameters and the pH is a determining factor due its directly relation to the redox reaction of the analyte, an analytical method for quantifying hydroquinone by chronoamperometry has been developed. A glassy-carbon working electrode, a reference electrode (Ag/AgCl) and a platinum auxiliary electrode were used. All of them immersed in an electrolytic cell filled with BR buffer solution adjusted to pH 5.5. The pH was chosen according to the condition the sample is kept. The optimized method is based on the hydroquinone oxidation by a 0.4 V fixed potential application, after the solution been kept stirring for 20 s. Some analytical validation parameters were verified. Selectivity and linearity were certified and the accuracy of the method was calculated by recovery tests at three concentration levels leading to a 98-111% range. A skin-bleaching gel sample containing 4% (w/w) of hydroquinone was tested following the optimized method. As a result, a concentration of 3.62% (w/w) was obtained. No trace of hydroquinone oxidation was found in the analyzed sample.