Introduction: Three original cosmetic formulations containing retinol as an active component with liquid crystal, lamellar, and lipid bases were prepared. The formulas contain different concentrations of retinol, that is, 0.5%, 0.3%, and 0.15%.
Objectives: The aim of the study was to evaluate a spectrophotometric method for assessing the quantity of retinol in the nine cosmetic products and to determine the viscosity of each formula.
Materials and methods: The formulations were tested for stability; final product testing was preceded by sample weighing and pH measurement as well as exposure to the light source from xenon lamp that maps solar radiation in the range of 310-800 nm. Microbiological purity test was performed according to the PN-EN ISO 29621:2011 method and viscosity carried out using a cone-plate digital rheometer (DV-III Brookfield, version 3.0) on 0.5 cm3 emulsion samples at 32°C. The retinol content in preparations was assayed by UV spectrophotometry.
Results: Each of prepared cosmetic products with retinol storing in a room temperature occurred to be stable. The liquid crystal emulsion has the higher viscosity than lamellar and lipid emulsions. Although the retinol concentration in lipid serum was determined with high accuracy, the method has some limitations associated with differences between the lipid cosmetic base and the lamellar and liquid crystal sera. Nevertheless, the UV spectrophotometric method described herein is a simple and highly accurate approach for determining the retinol content in lipid cosmetics: Its coefficient of correlation was R2 = 0.9982 with a relative standard deviation (n = 3) in the range of 0.5%-1.5%.
Conclusion: The presented UV spectrophotometric method represents an effective tool for fast and accurate determination of retinol content in lipid formulations. Probably, the method could be used in studies of other retinol-based preparations, for example, medications, and for determining the effective life of retinol-containing products in storage.
Keywords: cosmeceuticals; lipid; liquid crystal; retinoids; spectrophotometry; viscosity.
© 2020 Wiley Periodicals, Inc.