Confirmation of fluoroquinolones in catfish muscle by electrospray liquid chromatography/mass spectrometry

A multiresidue liquid chromatography/mass spectrometry (LC/MS) confirmation method for fluoroquinolones in catfish muscle was developed by using an electrospray interface. Residues of ciprofloxacin, enrofloxacin, sarafloxacin, and difloxacin were positively identified in catfish muscle fortified at 10-80 ppb as well as in incurred tissue. The extraction procedure is based on an LC method with fluorescence detection for determination of these compounds in catfish. Residues were extracted from catfish muscle with an acidic ethanol solution, and the extracts were cleaned up on a propyl sulfonic acid solid-phase extraction column. Chromatographic conditions were optimized to be compatible with the electrospray interface. Internal electrospray voltages were optimized so that 3 fragment ions, in addition to the protonated molecular ion, could be monitored for each residue. To obtain maximum sensitivity, separate MS acquisition programs were developed for ciprofloxacin/enrofloxacin and sarafloxacin/difloxacin pairs.