Determination and on-line clean-up of (fluoro)quinolones in bovine milk using column-switching liquid chromatography fluorescence detection

A simple, cost-effective, and high throughput method using on-line column-switching liquid chromatography fluorescence detection was developed and validated for analysing five (fluoro)quinolones (FQs)—enrofloxacin (ENRO), ciprofloxacin (CIPR), sarafloxacin (SARA), oxolinic acid (OXOL), and flumequine (FLUM) in bovine milk. Norfloxacin (NORF) and nalixidic acid (NALI) were used as internal standards. After simple deproteination of milk sample with 5% (w/v) metaphosphoric acid, the supernatant was subject to on-line column clean-up and direct analysis by LC–FLD. The extraction cartridge was prepared in-house by slurry packing with hydrophilic–lipophilic polymer sorbent. The accuracy of measurement for each (fluoro)quinolone at different maximum residue limits (MRL) was 101–103% (ENRO), 92.8–97.4% (CIPR), 89.8–92.8% (SARA), 116–121% (OXOL), and 81.3–85.5% (FLUM), whilst the precision was 2.9–6.1% (ENRO), 2.5–5.1% (CIPR), 2.3–5.0% (SARA), 3.1–5.9% (OXOL), and 5.6–6.5% (FLUM). The decision limits, detection capabilities, specificity and analytes stability during storage were also investigated.