Simultaneous quantitation of acetaminophen, aspirin, caffeine, codeine phosphate, phenacetin, and salicylamide by high-pressure liquid chromatography.

A method for the simultaneous quantitation of acetaminophen, aspirin, caffeine, codeine phosphate, phenacetin, and salicylamide was developed. The method is based on reversed-phase high-pressure liquid chromatography with a mobile phase buffered with phosphate (pH 2.3). The procedure not only separated these six active ingredients but also salicylic acid, the major decomposition product of aspirin. The method gave excellent results for three commercial products and a synthetic mixture containing four active ingredients. Lowering the pH increased the retention time of some weak acids and decreased that of some weak bases. Only these changes in the retention times made the separation possible.