Assay of mixtures of phenylpropanolamine hydrochloride and caffeine in appetite suppressant formulations by high-performance liquid chromatography.

A simple assay method for the quality control of appetite suppressant products containing phenylpropanolamine hydrochloride and caffeine has been developed. A methanolic extract of the product was evaporated to dryness and the residue was treated with aqueous solutions of sodium metaperiodate and disodium phosphate. Following addition of methyl p-hydroxybenzoate as internal standard and subsequent filtration, an aliquot of the filtrate was subjected to high-performance liquid chromatography on a 10-microns Partisil ODS-2 column with acetonitrile-water (30:70) as mobile phase. The drug: internal standard peak height ratio at 254 nm was linear over the ranges 0.3-2.0 micrograms of phenylpropanolamine hydrochloride and 1.1-16.0 micrograms of caffeine injected. All peaks were well-resolved. The heights equivalent to a theoretical plate (+/- S.D.) for phenylpropanolamine (as benzaldehyde) and caffeine were (n = 10) 0.42 +/- 0.08 and 1.31 +/- 0.23 mm, respectively. Overall per cent recoveries (+/- S.D.) from simulated formulations (n = 6) were 100.7 +/- 1.6% phenylpropanolamine hydrochloride and 99.1 +/- 1.4% caffeine. The method was applied to marketed products and is also applicable for single dose analysis.