A sensitive, specific and reproducible liquid chromatography coupled to tandem mass spectrometric method was developed and validated for the estimation of ciprofloxacin, an extensively used second-generation quinolone antibiotics, in human plasma. A liquid-liquid extraction of ciprofloxacin and the internal standard, ofloxacin, has been approached from the biological matrix using chloroform. Chromatographic separation was achieved in positive ion modes, isocratically on a 3.5 μm C18 analytical column (75 mm×4.6 mm, i.d.) with 0.2% formic acid solution in water: methanol (10:90, v/v) as mobile phase, at a flow rate of 0.5 mL.min-1. The MS/MS ion transitions were monitored as 332.0→231.3 for ciprofloxacin and 362.2→261.0 for IS. The method showed good linearity in the range of 0.01-5.00 μg.mL-1 (r2 >0.99) with a good precision (3.37-12.60%) and accuracy (87.25-114%). At the same time, ciprofloxacin was found to be stable during stability studies viz. bench-top, auto-sampler, freeze-thaw cycle and long-term. The developed and validated method was successfully applied to measure plasma ciprofloxacin concentrations in a single dose bioequivalence study.
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