Ultrahigh Resolution Semipreparative Liquid Chromatography: Application to Structure Elucidation of Drug Impurities

A research prototype high performance liquid chromatography (HPLC) system was built to prepare approximately 1 mg of drug impurities (purity > 90%) for structure elucidation by liquid state nuclear magnetic resonance (NMR). The system is based on alternate pumping (or twin column) recycling liquid chromatography. The system is coupled to a fraction collector and is designed to cope with severe experimental constraints, including situations where the impurity is barely separated from the active pharmaceutical ingredient (API); the drug diluent is strong relative to the eluent; viscous fingering occurs; the impurity-to-drug concentration ratio is extremely small (< 1/100); and where the yield and purity levels required should be larger than 99% and 90%, respectively. The combination of LC-mass spectrometry (MS) data and ultraviolet (UV) absorption spectra enabled the impurity to be identified.