A stability-indicating method for the determination of melphalan and related impurity content by gradient HPLC

A robust gradient high performance liquid chromatographic (HPLC) procedure is described for the simultaneous determination of melphalan content and related impurities in melphalan drug substance. The sample solution is prepared in methanol and injected. A linear gradient from 5 to 60% acetonitrile in water containing 0.05% v/v acetic acid, 0.01% v/v triethylamine, and 0.05% w/v ammonium acetate is applied over 20 min. The chromatographic conditions are capable of separating and quantifying all impurities found in routine production batches of melphalan at above 0.1% area/area. The method has been fully validated and is linear over the column loading range of 0–3 μg of melphalan. All related impurities occurring in routine batches at above 0.1% area/area have been identified, and structures assigned. The method has been applied to melphalan samples stored under stressed conditions, and shown to be stability-indicating.