Flow injection spectrophotometric determination of vitamin E in pharmaceuticals, milk powder and blood serum using potassium ferricyanide-Fe(III) detection system

A simple and sensitive flow injection spectrophotometric method is reported for the determination of vitamin E using potassium ferricyanide-Fe(III) detection system. In the presence of vitamin E, Fe(III)/ferricyanide reduces. The in situ reduced ions are then reacted with unreduced portion of ferricyanide/Fe(III) to make soluble Prussian blue, which is monitored at absorption wavelength of 735 nm. Linear calibration graph was obtained in the concentration range of 0.1-40 μg mL−1. The relative standard deviations (n = 4) were in the range of 1.1-3.6%, with limits of detection (3 s blank) of 0.04 μg mL−1. The proposed method allowed 12 injections h−1. The method is applied to determine vitamin E in pharmaceuticals, infant milk and blood serum samples using hexane extraction with the recoveries in the range of 93 ± 3 to 97.5 ± 4%. The method is validated using certified reference materials SRM 968c for blood serum samples.