| Popis: |
Different forms of tocopherols, together with tocotrienols, are collectively named as vitamin E (a lipid-soluble vitamin with antioxidation effect in several stages of peroxidation of lipids in vivo) and each possesses different degree of medical, biological and physiochemical significance. Among four tocopherols (α-, β-, γ- and δ-tocopherol), alpha-tocopherol has been reported to possess the highest biological activity. In order to obtain the larger amounts, vitamin E is synthesized as a racemic mixture of D- and L- forms which are optical isomers, unlike a natural tocopherol that is found only in the D-form. Synthetic vitamin E is derived from petroleum products as allracemic alpha tocopherol and its ester form all-racemic alpha tocopheryl acetate (or DL-tocopheryl acetate). The tocopheryl esters are more stable for an extended time of use. In the belief that vitamin E is a natural skin conditioner and humidifier, it is used in cosmetic industry in the preparation of lipsticks, shadows, powders, humidifiers, soaps, creams, shampoos etc. The recent popularity of vitamin E preparations for topical application, together with reports of adverse dermatological reactions linked to cosmetics containing this vitamin led to concern about the desirability of including these compounds in such products. Therefore, a sensitive, accurate and rapid HPLC method was developed for determination of alpha-tocopherol and its ester form in cosmetics. The chromatographic separation was performed on a column Purospher Star RP 18 (150 x 4.0 mm i.d., 5μm), with a mobile phase consisted of a methanol - n-hexane (90:10, V/V) The flow rate was kept at 1.2 ml min-1. Detection of all-racemic alpha-tocopherol and the ester form all-racemic alpha-tocopheryl acetate was carried out at 220 nm. Effect of various parameters (different concentration of methanol and n-hexane in the mobile phase composition and different columns used), and the separation of alpha-tocopherol and alpha-tocopheryl acetate from other numerous ingredients present in cosmetic preparations was studied. The proposed method was fully validated according to the ICH guidelines in terms of accuracy, precision, linearity, limit of detection and quantification and range (5). The method is sensitive and allows detection of active components in concentrations of 0,007 μg and 0,011 μg for α-tocopherol, and α-tocopherol acetate, respectively, while the lowest concentrations that could be determined were 0,023 μg, and 0,033 μg for α-tocopheryl acetate and α-tocopherol, respectively. |
