Simultaneous Determination of Vitamins A, D and E in Foods for Special Medical Purposes by Online Solid Phase Extraction Combined with Two-Dimensional Liquid Chromatography

A rapid method for the determination of VA, VD (VD₂, VD₃) and VE (α-, β-, γ-, and δ-vitamin E) in foods for special medical purposes was established using online solid phase extraction (SPE) combined with two-dimensional liquid chromatography (2D-LC). After saponification, enrichment and purification of VA, VD and VE from samples were accomplished on an online SPE cartridge. VA and four VEs were quantitatively analyzed by the first-dimensional LC, and VD was transferred by heart-cutting to the second-dimensional chromatographic system for separation and detection. SPE columns with different fillings, sample loading solvents, and eluent composition were evaluated, and 2D-LC conditions were systematically optimized. Good linearity was achieved for all vitamins tested with correlation coefficients (R²) greater than 0.997. The mean recoveries of the developed method were 84.4%–109.0% with relative standard deviation (RSD) of 0.34%–6.55% (n = 6). This method was highly automated with low detection errors and high detection efficiency, and could be used for the analysis of vitamins in foods for special medical purposes.