New spectrophotometric microdetermination of carbapenem antibiotics derivatives in pharmaceutical formulations

A new sensitive spectrophotometric method was developed to determine three carbapenem antibiotics: imipenem, meropenem and ertapenem. The proposed method was based on the formation of the coloured tris(o-phenanthroline)-iron(II) complex (ferroin) [Phen] or Fe (II)-2,2″-bipyridyl complex [Bip] in the reaction of the tested drugs with the corresponding iron (III)-complexes in an acetate pH 4 buffer. The formed coloured complexes showed maximum absorbance at 510 and 520 nm for [Phen] and [Bip], respectively. The reaction conditions, including the pH, reagent concentration, reaction time, temperature and stability of the formed coloured species, were optimized to achieve the highest sensitivity. Linear calibration curves were obtained in the concentration ranges from 0.2 to 10, 0.5 to 10 and 0.5 to 10 μg mL−1 for the aforementioned drugs in the same order. The developed method was successfully applied to determine the investigated carbapenems in their pharmaceutical formulations with average recoveries of 100.8, 99.8 and 99.4% for the Phen method and 98.9, 101.7 and 100.6% for the Bip method for imipenem, meropenem and ertapenem, respectively. A statistical comparison of the results with the reference method showed good concurrence and indicated no significant difference in accuracy or precision.