High-pressure liquid chromatographic assay of theophylline, ephedrine hydrochloride, and phenobarbital tablets.

An innovation high-pressure liquid chromatographic method is described in which theophylline, ephedrine hydrochloride (measured as benzaldehyde), and phenobarbital are determined simultaneously with butabarbital as the internal standard. Chromatographic conditions were selected to afford a pH sufficient for rapid oxidation of ephedrine and relatively high UV absorbance for the barbiturates and a detection wavelength near the maximum for benzaldehyde and the barbiturates and the minimum for theophylline. Chromatograms show peaks from iodate, theophylline, phenobarbital, butabarbital, and benzaldehyde, in order of increasing retention time, all within the dynamic range of a conventional recorder. Procedures are provided for the assay of conventional and sustained-action tablet formulations.