Rapid Separation Of Basic Drug Compounds Under Alkaline pH Conditions On pH-Stable, Short .C18 Column

By Derek Jensen and Mark Carrier, Hamilton Company

Mobile phase pH is a powerful tool in methods development, particularly for separation of neutral forms of amines or other organic bases under alkaline conditions. In this study a generic, 5-min linear gradient was used to separate six basic drug compounds on a short (50mm) PRP-C18 column.

More than 70% of all pharmaceutical drug compounds are cationic solutes that carry a formal positive charge below pH 7. Separation of these and other organic bases has historically been problematic. Ionization has a dominating effect in reversed phase chromatography that tends to dictate retention. Consequently, the elution window for a sample of ionized amines is narrow. The task is further complicated by secondary interactions that occur between positively charged solutes and residual silanols on the column stationary phase. These secondary mechanisms of retention are the principle source for anomalous chromatographic activity, such as poor peak shape, shifts in retention times and loss of efficiency that progressively worsen over the life of the column.