Spectrophotometric Determination of Some Antibiotics Using Bromophenol Blue as Ion Pair Reagent

Abstract

Objective: Simple and rapid methods have been developed for the determination of azithromycin, sparfloxacin and cephalexin monohydrate in bulk and pharmaceutical formulations. Method: These methods were based on the formation of bluish-green ion pair complexes of these antibiotics with bromophenol blue (BPB). Acetonitrile was used as a solvent for azithromycin and sparfloxacin whereas methanol-acetonitrile medium for cephalexin monohydrate. Results: 2:1 complexes were formed between the drug and reagent almost instantaneously with absorption maxima 595 nm, 620 nm, 600 nm for the three drugs respectively. Different parameters such as effect of time, effect of reagent concentration were optimised. Under optimum conditions, calibration curves were found to be linear over the range of 0-50 μg mL -1 for azithromycin, 10-80 μg mL -1 for sparfloxacin and 10-170 μg mL -1 for cephalexin monohydrate respectively. The detection limits were found to be 0.10 μg mL -1 , 0.21 μg mL -1 and 1.69 μg mL -1 with Sandell's sensitivity 0.0559 μg cm -2 , 0.1034 μg cm -2 and 1.3920 μg cm -2 respectively for the three drugs. Stability constant (log K) was found to be 6.19 ± 0.04, 5.00 ± 0.07 and 4.05 ± 0.05 showing high stability of the complexes. Molar absorptivity was found to be 1.369×10 4 L mol -1 cm -1 , 3.774×10 3 L mol -1 cm -1 and 2.620×10 2 L mol -1 cm -1 with Gibb's free energy change -2.725×10 3 kJ mol -1 , -2.393×10 3 kJ mol -1 and -1.938×10 3 kJ mol -1 . These methods were subjected to analytical quality control. Accuracy, precision, recovery and interference studies have been carried out. Conclusion: The proposed methods were successfully applied to the determination of these drugs in their pharmaceutical formulations and human urine samples.