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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