Simultaneous determination of retinol and alpha-tocopherol in polymeric diets for enteral nutrition

Existing methods for simultaneous measurements of retinol and alpha-tocopherol in enteral formulas require large sample and solvent volumes and are time-consuming and costly. We have developed a simple, sensitive, cost-effective method for the determination of these vitamins in polymeric diets that can easily be applied to standard quality control of large numbers of samples. Our analytical procedure comprises deproteinization with pure ethanol, saponification with a 3.6M KOH solution in a sonicator for 30 min at 65 degrees C under a nitrogen atmosphere, solubilization of samples in phosphate buffer and extraction with hexane. Vitamins are separated by reversed-phase HPLC and quantified by dual-wavelength spectrophotometry. The method gives satisfactory results, with recovery rates of 106.3+/-1.5% for retinol and 102.3+/-1.5% for alpha-tocopherol and RSDs ranging between 1.2 and 4.8% for precision. This method is suitable for the quality control of enteral formulas.