Analysis of pharmaceutical formulations containing ampicillin and cloxacillin using second-derivative spectroscopy on a diose-array spectrophotometer

Two-component mixture of ampicillin and cloxacillin with considerable overlapping spectra was assayed by a second-derivative spectrophotometric method using a diode-array spectrophotometer. The second-derivative spectra of sample solutions in distilled water were scanned between 260 and 300 nm. Derivative measurements were carried out at 269 nm [zero-crossing], and at 288 nm [peak-to-zero] for ampicillin and cloxacillin, respectively. The procedure does not require any separation step or chemical reagents and allows for a single-unit assay for normal dosage used. Beer's law holds up to 14 mg% for both penicillins. The method was successfully applied to commercial preparations containing a binary mixture of both penicillins