A New Visible Spectrophotometric (VIS) Method for the Quantitative Analysis of Vitamin E (alpha-D-Tocopherol) in Capsules of a Food Supplement

Vitamin E is an very effective and powerful antioxidant which inhibits and blocks the synthesis of free radicals, with high carcinogenic potential for humans. Alpha-D-Tocopherol is always brought in through a balanced food intake that includes the regular daily consumption of nuts, seeds ,almonds, peanuts, hazelnuts, and oils, as well as certain fish such as salmon, vegetables, such as red sweet pepper, and fresh fruits like avocado, mango, and kiwi fruit. Our main aim was to exactly determine the pure amount of vitamin E (alpha-D-Tocopherol as single active substance) in a soft-release capsule using a new spectrophotometric method in a visible range. Finally, the obtained result was compared with the official amount of active substance in the soft release capsule, according to Romanian and European Pharmacopoeias rules. The method was based on the complete oxidation of alpha-D-Tocopherol with an acidified solution of FeCl₃ in a H₂SO₄ 30% solution, obtaining a final oxidation product with the terminal CH₂-OH primary group (omega oxidation). At the same time, the ferric ions were reduced to ferrous ions Fe²⁺, which were quantitatively complexed in the dark with free unreacted ferric Fe³⁺ ions from a potassium ferricyanide K₃[Fe (CN)₆] solution. The Turnbull blue compound was quantitatively obtained and was dosed at its absorption maximum wavelength λ = 705 nm. The amount of alpha-D-Tocopherol found in the soft-prolonged-release capsule was 97.48 mg pure active substance/soft capsule. The amount found was very close to the reference value of 100 mg pure α-D-Tocopherol in prolonged-release capsules, in relation to the average mass of a capsule 270,2 mg, and corresponded to a real content percentage found of 97.48 mg % pure alpha-D-Tocopherol/prolonged-release capsule. The average percentage error was only 2.516 % below the reference value (100 mg). This method was subjected to full statistical validation and was validated. The sensitivity of the measurement was found to be S = 0.0158 µg/cm³ = 15.8 ng / cm³ for 97.48 mg pure content of alpha-D-Tocopherol in the capsule.