Selective spectrophotometric determination of phenolic β-lactam antibiotics in pure forms and in their pharmaceutical formulations

Four simple and selective spectrophotometric methods were developed for the quantitative determination of some phenolic β-lactam antibiotics (amoxicillin trihydrate, cefoperazone sodium, cefadroxil monohydrate, and cefprozil anhydrous) in pure forms as well as in their pharmaceutical formulations through their nitration and subsequent complexation with an nucleophilic reagent (method I), nitrosation and subsequent metal chelation (method II), coupling with diazo reagent (method III), and reaction with copper and extraction of the resulting chelate into chloroform (method IV). The reaction conditions were studied and optimized. Beer’s plots were obeyed in a general concentration range of 5-30 ug ml⁻¹ with correlation coefficients not less than 0.9997 for the four drugs. The methods are successfully applied to the analysis of pharmaceutical formulations containing amoxicillin, either alone or in combination with potassium clavulanate. They were also applied to the analysis of the other three studied drugs in vials, capsules, tablets, and suspensions with good recovery; percentage ranged from 99.0 (±1.42) to 100.2 (±1.25) in method I, 99.0 (±0.82) to 100.5 (±0.92) in method II, 99.5 (±0.09) to 100.8 (±0.98) in method III, and 99.3 (±0.01) to 100.2 (±0.05) in method IV. Interferences from other antibiotics and additives were investigated.