Indirect Spectrophotometry Method Based on the Formation of Chromium(VI)-Diphenylcarbazide Complex for Determination of Hydroquinone in Cosmetics

This research is focused on the development of a new indirect spectrophotometry for the determination of hydroquinone in cosmetics based on the capability of hydroquinone as reducing agent for chromium(VI). The principle of the determination is based on the decrease of the color intensity of the red-violet complex of chromium(VI)-Diphenylcarbazide (DPC) due to the reduction of the available chromium(VI) by hydroquinone to chromium(III). Thus, only the remaining chromium(VI) reacted with DPC to form a red-violet complex detected by spectrophotometry at 542 nm. All chemical parameters were optimized with respect to sensitivity and selectivity of measurements. Under the obtained optimum conditions (reaction time of 5 minutes, chromium(VI) of 1 mgL −1 , sulfuric acid of 0.05 M, and DPC of 0.0125%), the method gave linear calibration for hydroquinone concentration from 0.2-2.5 mgL −1 (R 2 = 0.996). The proposed method also provided good sensitivity shown by low values of LoD and LoQ (0.07 and 0.1 mgL −1 ) and satisfactory selectivity towards the common interfering ions present in cosmetics. Satisfactory results with recoveries of close to 100 % were observed when the method was applied to facial whitening and black spot removal cosmetics. This result suggests that the developed method is able to be used for monitoring of hydroquinone in skin lightening cosmetics.