Development and validation of a generic stability-indicating MEEKC method for five fluoroquinolone antibiotics

In this paper, a reliable stability-indicating generic MEEKC method for the analysis of five commonly used fluoroquinolones (FQs) has been developed and optimized by a central composite circumscribed experimental design. The separation was carried out using a fused silica capillary (60.2 cm total length) and a microemulsion (ME) composed of 81.75% (w/w) of a 125 mM NaH₂ PO₄ solution having a pH of 2.75, 2.65% (w/w) SDS, 1.00% (w/w) n-octanol, 6.60% (w/w) n-butanol and 8.00% (w/w) 2-propanol. A voltage of 28 kV was applied in a reverse polarity mode. A linear relationship was established from 0.04 to 0.48 mg/ml with R² values higher than 0.98 for all five FQs. Both repeatability and intermediate precision were less than 3% and accuracy ranging from 97 to 100%. Of note, ciprofloxacin impurity A and ofloxacin impurity A could be separated from the respective drug substance in a single run which cannot be achieved using the official HPLC method from the European Pharmacopoeia. Forced degradation of all FQs under heat, in acidic and alkaline medium, in the presence of oxidizing agents and under neutral hydrolysis conditions was investigated. The highest yield of degradation products was observed using oxidative hydrogen peroxide. Hence, the proposed MEEKC method can be used for the quantitative determination of the five FQs and their potential impurities within a total runtime of 20 min.