Coenzyme Q10 and vitamin E are lipid-soluble antioxidants, which protect the skin from free radicals and are therefore widely used in anti-age cosmetics. Since the concentration of these compounds is not declared on any of the products on the market, our main goal was to determine whether they are present in the selected products, to evaluate their concentrations as well as their stability under different conditions. For such purposes previously developed HPLC-UV method was used. The method was validated in terms of selectivity, linearity, repeatability, precision, accuracy, and sample stability. Simple extraction procedure was optimized and validated, confirming high extraction recovery and good repeatability of the sample preparation. 22 cosmetic products of different brands, price range and type, with declared coenzyme Q10 and/or vitamin E (single or as acetate) were analyzed and compared regarding to the brand, price range and type of cosmetic product. Majority of the products contained all the compounds listed on the packaging, although some products contained compound that was not specified. Coenzyme Q10 was found in all products which declared it, but its reduced form was not found in any of tested products. In the tested cosmetic products coenzyme Q10 and vitamin E were present in microgram and vitamin E acetate in miligram quantities (per 1 gram of product). Correlation between coenzyme Q10 concentration and the quality and price of the product was not found. Moreover, its concentrations in day and night skin care products were almost the same. The stability of these compounds in different products was further checked with accelerated tests (1 month, 40 °C), exposure to the UV light and storage at the room temperature in the original package for one month after opening. The results of accelerated testing showed that coenzyme Q10 and vitamin E acetate were stable under these conditions. All of the three compounds were found sensitive to UV light, among which vitamin E acetate was the most photostable. Coenzyme Q10 was also more stable in day creams with sun protection factor than in night creams. Based on the stability testing it can be concluded that coenzyme Q10 and vitamin E are not photostable so the protection of product and compound from UV light is very important.
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