Simple and Specific Assay of Penicillins by IR Spectrophotometry in Deuterium Oxide and Dimethyl Sulfoxide Solutions

Abstract

An IR spectrophotometry method for the qualitative and quantitative analysis of penicillins is described. The method is based on the inspection of the carbonyl region of the IR spectrum of penicillins dissolved in deuterium oxide or dimethyl sulfoxide solution and on the measurement of the absorbance of the -lactam band at about 1760 cm−1. Most common natural and synthetic penicillins are amenable to the present IR analysis in solution, without previous derivatization. The accuracy of the method is better than ±2% and is thus comparable to that usually attainable by current iodometric procedures. Since the solution spectra in the analytical region are characteristic for the individual penicillins, the described method is superior to iodometry as far as specificity is concerned. A single analysis usually requires no more than 15 min. The method allows a direct evaluation of the stability of penicillins in aqueous (deuterium oxide or deuterium chloride) solutions. Usual salts or buffers generally do not interfere with the analysis. Some qualitative and quantitative aspects of the IR spectra of penicillins in solution are discussed.