A HILIC method for the analysis of tromethamine as the counter ion in an investigational pharmaceutical salt

A hydrophilic interaction chromatography (HILIC) method using an aminopropyl stationary phase was developed and validated to determine the content of tromethamine as counter ion in an investigational drug substance. Tromethamine was a very polar compound without any chromophores, and could not be readily retained and detected by conventional reserved-phase HPLC-UV methods. Furthermore, the tromethamine salt of the drug compound also had limited solubility in aqueous solution. The method employed simple acetonitrile/water mobile phase (80/20, v/v) to provide sufficient retention for tromethamine. Meanwhile, the high acetonitrile content also helped to dissolve the drug substance sample. Refractive index (RI) was used for the detection of tromethamine. The method was found to be specific without interference from the drug compound and related impurities. The method was also validated for suitable precision, linearity and accuracy for the analysis of drug substance samples. The effects of various parameters, such as acetonitrile content, mobile phase salt concentration, and column temperature on HILIC separation were investigated. (C) 2003 Elsevier Science B.V. All rights reserved.