Circular dichroism spectroscopy: An efficient approach for the quantitation of ampicillin in presence of cloxacillin

•CD spectra of ampicillin showed negative cotton band peaking at 206 nm.•Ampicillin could be selectively determined in presence of cloxacillin.•Accurate and precise method and could be easily applied in quality control laboratories.

Ampicillin exhibited a negative and a positive cotton effects on the circular dichroism (CD) spectra in the wavelength range of 200–280 nm. Cloxacillin showed a positive cotton band peaking at 228 nm. Three sensitive, precise and accurate CD spectroscopic methods have been developed for the determination of ampicillin and cloxacillin. Method A was used for the determination of ampicillin in presence of cloxacillin by measuring ellipticity at 206 nm. Method B and C were employed to determine ampicillin and cloxacillin based on evaluation of ellipticity at 233 nm and 228 nm, respectively. Methods A, B and C showed linearity in the concentration range of 10–40 μg mL− 1, 5–40 μg mL− 1 ampicillin and 10–80 μg mL− 1 cloxacillin, respectively. The method A was successfully applied to the determination of ampicillin in commercial dosage forms containing equivalent amount of cloxacillin.

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