J. Cosmet. Sci., 61, 353–365 (September/October 2010) 353 Analysis of vitamin E in commercial cosmetic preparations by HPLC ALY NADA, YELLELA S.R. KRISHNAIAH, ABDEL-AZIM ZAGHLOUL, and IBRAHIM KHATTAB, Faculty of Pharmacy, Kuwait University, Kuwait (A.N., A.-A.Z., I.K.), and College of Pharmacy, Nova Southeastern University, Ft. Lauderdale, Florida (Y.S.R.K.). Accepted for publication May 13, 2010. Presented at the AAPS Physical Pharmacy and Biopharmaceutics Workshop, Baltimore, Maryland, May 13–15, 2009. Synopsis A specifi c HPLC method, with an RP–C-18 column and a UV detector, for simultaneous determination of vitamin E (tochopherol, T)/T acetate (TA) in four commercial and two experimental cosmetic products is de- scribed. Three solvent systems for extraction of T/TA were assessed: isopropyl alcohol 10:90 v/v hexane-methanol mixture (method 1) and methanol alone (method 2). The procedure was accurate, as indicated by high recov- ery (97.8–101.8% and 100.1–102.5% for T and TA, respectively) and precise (RSD was only 0.9–3.26% and 0.73–3.35% for T and TA, respectively). The limits of detection for T and TA were 200 and 300 ng/ml, re- spectively, while the limits of quantitation were 250 and 400 ng/ml, respectively. The range of reliable quan- tifi cation was 5–50 μg/ml. Isopropanol as solvent resulted in a turbid extract. Method 1 and method 2 of extraction showed high recovery (98.5–99.9% and 97.2–97.9% for T and TA, respectively). After a few weeks of analysis, method 1 resulted in retention time drift, peak broadening, non-reproducible results, and progres- sive loss of HPLC-column integrity. Methanol alone (method 2) was equally as effi cient as that of the mixture of methanol with 10% hexane (method 1) for extraction. The described analytical procedure proved to be ac- curate, precise, and suitable for simultaneous determination of T and TA in real commercial cosmetic products. INTRODUCTION Cosmetic changes associated with aging, especially in the face, are particularly concern- ing to the patient/consumer population that wishes to remain looking youthful all the time. Inclusion of botanical extracts such as vitamins and anti-microbials to cosmetics has become an important marketing advantage. These ingredients have the appeal of appear- ing wholesome and “organic.” Although scientifi c evidence shows that some of these in- gredients do have some in vitro anti-aging activity, the question remains as to whether it is possible to deliver adequate doses to the skin in vivo (1). Vitamin E is one of the best established ingredients in OTC products for skin aging. It is a lipid-soluble antioxidant that plays key roles in protecting cell membranes from lipid peroxidation by free radicals and in reducing photocarcinogesis (2–4). Thiele et al. concluded that α-tocopherol is the Address all correspondence to Aly Nada.
JOURNAL OF COSMETIC SCIENCE 354 major antioxidant in the human epidermis, and that its depletion is an early and sensitive marker of environmental oxidative damage (5). Vitamin E is available as the free alcohol or its esters, and the benefi cial effects of vitamin E-containing cosmetic products depend on the concentration of added T and/or TA as well as their stability. Several analytical methods have been used to estimate the concentration of T and TA in pharmaceutical/cosmetic products and food supplements (6–8). Ruperes et al. reviewed chromatographic analysis of T and related compounds in food, pharmaceu- ticals, plants, animal tissues, etc., and pointed out the complications of the matrix in the analytical method (9). The authors indicated that sample preparation is a critical step, is time-consuming and expensive, and is the main source of errors in the analytical method. Moreover, it is worthwhile to mention that working with cosmetic products represents additional diffi culties due to the presence of many excipients/vehicles, e.g., fats, oils, and waxes, that possess a similar lipophylic nature as the analytes. Such materials are usually present in very high concentrations relative to the vitamins, which further complicates the analytical process. Although numerous methods for determination of T derivatives in pharmaceuticals such as tablets and capsules are described in the literature, no typical ana- lytical methods for determination of T and TA in actual commercial cosmetic products have been published (9). Guaratini et al. (8) reported on the stability of experimental cos- metic gel-cream formulations containing vitamin E acetate and vitamin A palmitate. Re- cently, Almeida et al. (10) documented an HPLC method for determination of tocopheyl acetate and ascorbyl tetraisopalmitate in an experimental cosmetic formulation. However, both studies (8,10) applied the proposed analytical methods on lab gel formulation, which in fact does not resemble the complex lipid matrices commonly encountered in commer- cial cosmetics. In addition, Dingler et al. (11) reported on an HPLC method for determina- tion of T in a dermal product however, the authors applied only cetyl palmitate as the lipid carrier, which does not simulate the actual complex nature of commercial products. Hence, the present study was carried out to develop a specifi c, precise, and accurate HPLC method for simultaneous determination of both T and TA in real commercial cosmetic prod- ucts. The investigation was focused on the development of an extraction procedure to selec- tively pick up the vitamin/ester from such cosmetics with good extraction effi ciency and to leave the commonly associated lipophylic materials. The results of the proposed HPLC method were validated using two experimental cosmetic creams simulating the complex cosmetic bases commonly experienced in real commercial products, each containing about 0.5% of T or TA, as well as four marketed cosmetic cream products containing TA. EXPERIMENTAL MATERIALS The methanol, acetonitrile, hexane, and ethanol used in the study were of HPLC grade (Merck, Darmstadt, Germany). Vitamin E acetate was obtained from BASF, Ludwig- shafen, Germany. Vitamin E, soybean oil, and corn oil were procured from Sigma Aldrich Chemie GmbH, Steinheim, Germany. Propylene glycol (Generico Medical Practice, AB Almere, Holland), stearic acid, white soft paraffi n, potassium hydroxide (Loba CHEMIE- India), lanoline, glycerol, sorbitol (Gainland Chemical Company, UK), Captex SBE, and Acconon S-35 (ABITEC Corporation, Janesville, USA) were of analytical grade.
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