Interlaboratory verified liquid chromatographic method for analysis of vitamins A and E in soy-based infant formula...

An interlaboratory verified, liquid chromatographic (LC) method is presented for the analysis of all-rac-alpha-tocopheryl acetate and retinyl palmitate in soy-based infant formula. The extraction procedure uses sample dehydration with magnesium sulfate followed by extraction with isopropanol, hexane-ethyl acetate (85 + 15, v/v). After evaporation and filtration, the sample extract is injected directly onto a normal-phase LC system with fluorescence detection. All-rac-alpha-tocopheryl acetate and retinyl palmitate are quantitated isocratically with a mobile phase of hexane containing 0.50% (v/v) and 0.125% (v/v) isopropanol, respectively. A zero control reference material (ZRM) was spiked at 5 levels, with 5 replicate analyses of 1/2x, x, 2x, 4x, and 16x where "x" is the minimum level of 250 IU/100 kcal (vitamin A) and 0.7 IU/100 kcal (vitamin E) as specified in 21 Code of Federal Regulations 107.100. The following recoveries and RSD values represent an average (n = 25) of the 5 levels for each analyte: all-rac-alpha-tocopheryl acetate, 100% (RSD = 3.5%); retinyl palmitate, 97.2% (RSD = 2.1%). Two additional laboratories analyzed the fortified ZRM samples. Average recoveries (n = 24) of all-rac-alpha-tocopheryl acetate and retinyl palmitate at 4 levels were all-rac-alpha-tocopheryl acetate, 99.0% (RSD = 4.0%), and retinyl palmitate, 96.2% (RSD = 1.4%) at the second laboratory. Average recoveries (n = 24) of all-rac-alpha-tocopheryl acetate and retinyl palmitate at 4 levels were all-rac-alpha-tocopheryl acetate, 102% (RSD = 1.4%) and retinyl palmitate, 95.7% (RSD = 2.0%) at the third laboratory. In addition, 6 replicates of the same commercial soy-based infant formula powder were run by the 3 laboratories.