Analysis of Ciprofloxacin in Low- and High-Fat Milk by High-Performance Liquid Chromatography-Mass Spectrometry

The quantitative analysis of antibiotics in different matrices is of increasing importance in in vitro studies of food-drug interactions in the drug-development process. Our objective was to develop a new, rapid and simple solid-phase extraction method without protein precipitation followed by high-performance liquid chromatography coupled with mass spectrometry (HPLC-MS) for analysis of ciprofloxacin in low- and high-fat milk. The HPLC-MS method (a single-quadrupole mass spectrometer equipped with an electrospray ion source was used as detector) was validated using a quinolone derivative, aripiprazole, as internal standard. A C-8 column and gradient elution with 0.02 M ammonium acetate solution (pH 2.5) and acetonitrile mixtures (flow rate 0.5 mL min(-1)) were used for HPLC separation. Various modes of detection (diode-array detection and MS detection in scanning and selected-ion monitoring modes) were compared for selectivity and sensitivity of quantitative analysis of ciprofloxacin. Use of selected-ion monitoring resulted in a 1600:1 signal-to-noise ratio which can be successfully applied to milk matrices resulting in a lower limit of detection of 0.4 ng mL(-1) and a lower limit of quantification of 4.0 ng mL(-1). Recovery was 99.06 +/- 0.15 and 98.57 +/- 0.14% for low- and high-fat milk, respectively. The method enables analysis of the free, biologically available, amount of ciprofloxacin in in vitro simulation of milk-ciprofloxacin interaction studies.