Determination and Control of Genotoxic Impurity in Vitamin E, Drug Substance

Vitamin E (alpha-tocopherol) is a lipid-soluble antioxidant. p-toluenesulfonic acid, used as reagent in the synthesis of alpha-tocopherol, has a sulphonate group, a well-known alerting function for genotoxic activity. Genotoxic impurities in pharmaceuticals at lower levels are of increasing concerns not only to pharmaceutical industries but also for the regulatory agencies due to their risks for human carcinogenesis and, thus, requiring manufacturers to pay extra attention for their analysis and control. Therefore, sensitive and sophisticated analytical methodologies are deemed necessary in order to be able to test and control genotoxic impurities in drug substances. This work describes a simple, accurate and sensitive reversed-phase liquid chromatography—UV method for determination of trace amount of p-toluenesulfonic acid in pharmaceutical materials. A gradient mobile phase consists of acetonitrile and 0.01M potassium dihydrogen orthophosphate in water adjusted pH 3.0 with 0.1% phosphoric acid. Chromatography was carried out at ambient temperature 25°C on a Waters HPLC column C18, 150 mm x 4.6 mm, 5?m. The detection was carried out using variable wavelength UV-Vis detector set at 222 nm. The compounds were eluted at a steady flow rate of 1.0 mL/min. P-toluenesulfonic acid retention time was about 6.0 min with an asymmetry factor of 1.0. A logarithmic calibration curve was obtained from 0.1 to 3 µg/mL (r > 0.9998). Within-day %RSD was 0.21 (n = 5, 0.002 mg/mL) and between-day %RSD was 0.35 Specificity/ selectivity experiments revealed the absence of interference, recovery from spiked samples was between 97.6–103.78 percent. The developed method was applied to the determination of p-toluenesulfonic acid in pharmaceutical drug substance and drug product.