High-performance liquid chromatographic and derivative ultraviolet spectrophotometric determination of amoxycillin and dicloxacillin mixtures in capsules.

Two rapid assay procedures based on high-performance liquid chromatography (HPLC) and derivative ultraviolet (UV) spectrophotometry have been developed for the simultaneous determination of amoxycillin and dicloxacillin in two-component capsule formulations. The HPLC determination was carried out on a reversed-phase C8 column with use of a mobile phase consisting of methanol-0.02 mol dm-3 ammonium acetate (pH 5) (50 + 50) at a flow rate of 1.0 cm3 min-1, with UV detection at 230 nm. The fourth-derivative spectrophotometric procedure depends on the measurement of the derivative amplitudes, in 0.1 mol dm-3 NaOH, at 308.5 and 275 nm for amoxycillin and dicloxacillin, respectively. For both procedures, the calibration graphs were linear in the ranges 20-200 and 20-140 micrograms cm-3 for the HPLC and UV derivative methods, respectively, with an almost zero intercept and a correlation coefficient of 0.999. Commercial capsules and laboratory-prepared mixtures containing both penicillins in different proportions were assayed by the developed procedures. The results were of comparable accuracy as indicated by a statistical analysis of the data, using both t- and F-tests.