A Sensitive and Simple HPLC-UV Method for Trace Level Quantification of Ethyl p-Toluenesulfonate and Methyl p-Toluenesulfonate, Two Potential Genotoxins in Active Pharmaceutical Ingredients

A sensitive and simple HPLC/UV method has been developed and validated for the determination of two potential genotoxic impurities, namely methyl p-toluenesulfonate (MPTS) and ethyl p-toluenesulfonate (EPTS) at trace levels in Pemetrexed sodium API. Applying the concept of threshold of toxicological concern (TTC), a limit of 3 ppm each for both genotoxins was calculated based on the maximum daily dose of API. A reversed phase LC method using UV detection was developed and validated. The method was found to be specific and selective for the application. The limit of detection (LOD) and limit of quantitation (LOQ) for both MPTS and EPTS was found to be 0.15 ppm (0.009 μg mL⁻¹) and 0.5 ppm (0.03 μg mL⁻¹), respectively, with respect to sample concentration. The calibration curves of MPTS and EPTS were linear over the concentration range from LOQ to 6 μg/mL. The method was found to be specific, precise, linear and accurate and has been successfully applied to determine the two genotoxins in commercial batches of the API.