Highly sensitive spectrometric method for determination of hydroquinone in skin lightening creams: application in cosmetics.

A highly sensitive, simpler, faster and economical UV/visible spectrophotometric method has been established for the estimation of hydroquinone (HQ) in dilute organic matrices. The method is based on using ammonium meta-vanadate as an oxidizing catalyst for conversion of HQ to p-benzoquinone (BQ) in the presence of oxygen. As a result of higher absorption of UV light by BQ than by HQ, its signal has been utilized for determining HQ at the trace level. The effect of various parameters such as amount of oxidizing agent, stability time, temperature, acids and bases, solvents and interference by various compounds has been studied upon the absorption of BQ as HQ. Under optimized conditions, Beer's Law was obeyed in the range of 0.025-2.00 μg ml(-1) HQ at 245.5 nm using 1 : 1 (V/V) 2-propanol/water system with a lower detection limit of 7 ng ml(-1) and linear regression coefficient of 0.9998. Relative standard deviation of 1.5% was observed for 0.5 μg ml(-1) HQ solution (n = 11). The newly developed method has been successfully applied to diluted samples of various skin lightening creams for free HQ determination at the trace level. Comparison of the results obtained by the proposed method with those by a previously reported method proved its validity.