Quantification and targeted detection of ciprofloxacin in dosage form and human urine by direct injection nano-electrospray ionization multi-stage mass spectrometry

A rapid, selective and sensitive direct infusion nano-electrospray ionization multi-stage mass spectrometry (DI-nano-ESI-MS3) method has been developed and validated for ciprofloxacin identification and quantification. An aliquot of 4 mu l containing ciprofloxacin sample solution along with an internal standard (IS), in this case tamoxifen, was loaded into a nanospray (NS) capillary. The NS capillary was then fitted off-line into the ion source where the distance between NS capillary tip and MS aperture was set to 5 mm. The instrument was operated to acquire a two-minute run by applying a voltage of 1000 V (positive-ion detection mode). Ciprofloxacin quantification relied on the ratio of its parent peak (m/z 332) to the IS peak (m/z 372), while identification relied on MS3 of the parent peak and its fragments with m/z values of 314, 288, 268 and 245, respectively. Due to the observed ion suppression effect exerted by the IS over the analyte ion signal at lower concentration levels (< 500 ng/ml ciprofloxacin), the calibration curve was split into two sections. As a result, linearity correlation between the ratios of the analyte to the IS and the corresponding concentrations over the ranges 5-500 and 500-4000 ng/ml respectively was observed. The applicability of the developed method was confirmed by analyzing ciprofloxacin in a pharmaceutical dosage form as well as detection of the analyte in random human clinical urine samples after oral administration of the drug.