Curcumin quantification in skin and mucosa: Optimization of extraction and chromatographic method validation

Curcumin is a natural phenol found in the rhizome of Curcuma longa. It has been studied to treat several human carcinomas, such as melanomas and breast, head and neck, prostate, and ovary cancers. Here, we develop and validate a method for recovering curcumin from the skin layers and mucosa and selectively quantifying it, aiming to support permeation studies in developing topical formulations containing the natural compound. Recovery of curcumin from the stratum corneum, remaining skin, and mucosa was performed using ethanol, DMSO/ethanol, and DMSO, respectively, under mild stirring for specific periods. The separation of curcumin from the other curcuminoids, skin, and mucosa interferents was obtained using a C₁₈ column as a stationary phase. The mobile phase was composed of pH 3.0 phosphoric acid at 1.0 mmol/L and acetonitrile (47:53, v/v), which flowed at 1 mL min^-1. UV-Vis detection of curcumin was at 424 nm. The chromatographic method was selective, linear (r > 0.999), with a regression curve in the concentration range from 1.0 to 30.0 μg mL^-1, robust, precise, and accurate, with curcumin recovery rates higher than 95 ± 7 % from the mucosa, 82 ± 2 % from the stratum corneum, and 65 ± 10 % from the remaining skin. Finally, the method was successfully used in a skin permeation test performed with porcine skin and mucosa. The validated method is, therefore, suitable for the recovery and quantification of curcumin from the skin layers and mucosa, favoring the development of new topical formulations destined for these sites of administration.