High-Pressure Liquid Chromatographic Separation of Diphenhydramine and Some of its Metabolites: Effects of Eluent Salt Concentration on Chromatographic Characteristics

With appropriate variation of the pH, alkali halogenide concentration and cation and/or anion species in the mobile phase (mixtures of water and methanol), it was possible to resolve diphenhydramine, N-desmethyldiphenhydramine, N,N-didesmethyldiphenhydramine, benzhydrol, benzophenone and 2-methyldiphenylmethoxy acetic acid on a reversed-phase column. The retention volumes of the three amines decreased by increasing the following parameters: salt concentration, methanol concentration and cation and/or anion size. The retention volumes of the other compounds were not influenced. The good separation and the simplicity make this method attractive for use in metabolism studies.