Quantitative analysis of retinol and retinol palmitate in vitamin tablets using 1H-nuclear magnetic resonance spectroscopy

1H-NMR spectrometry was applied to the quantitative analysis of Vitamin A in four different types of vitamin tablets without any chromatographic purification or saponification. The experiment was performed analysing the H-15 resonance, which appears at (delta) 4.32 for retinol and (delta) 4.69 for retinol palmitate, well separated from other resonances in the 1H-NMR spectrum. Compounds were quantified using the relative ratio of the integral of the H-15 signal to that of a known amount of internal standard (200 (mu)g/ml), anthracene. In order to evaluate the feasibility of avoiding the saponification of retinol palmitate in the preparation of samples, several solvents such as dimethylsulfoxide, n-hexane, methanol, water, and 0.1 M of HCl were tested as possible extraction solvents. Among these, dimethylsulfoxide showed the best yield of retinol palmitate. This method, using dimethylsulfoxide extraction and 1H-NMR, allows rapid and simple quantitation of retinol palmitate in tablets avoiding tedious saponification.