A spectrofluorimetric procedure for the determination of α-tocopherol in nutritional supplement products

A direct spectrofluorimetric method for the determination of vitamin E in nutritional supplement products is described. Samples analysed include single vitamin and multivitamin tablets and capsules as well as dietary formula preparations. The analytical procedure was carried out in a single reaction vessel and consisted of saponification of samples for 10 min in a water bath set at 85°C using absolute ethanol (5 ml) and 80% (w/v) potassium hydroxide solution (2 ml) as the saponification medium, with ascorbic acid (125 mg) as antioxidant. The analyte was extracted in situ with n-hexane (20 ml). Treatment of the n-hexane layer with 60% (v/v) sulphuric acid (2 ml) was sufficient to remove interference by retinol, and the n-hexane layer was then used for direct fluorescence measurement at 298 nm (excitation) and 330 nm (emission). The scanning of several excitation and emission spectra of sample extracts, showed no evidence of interference by any excipient matter or extraneous fluorescing lipid soluble components. Vitamin E values obtained using the described procedure showed good agreement with manufacturers' label expectations.