Determination of (fluoro)quinolones in environmental water using online preconcentration with column switching linked to large sample volumes and fluorescence detection

An analytical method based on online enrichment using coupled‐column liquid chromatography with fluorescence detection has been developed to determine marbofloxacin, ciprofloxacin, danofloxacin, enrofloxacin, norfloxacin, lomefloxacin, oxolinic acid, and nalidixic acid at trace levels in surface water. The sample containing the pharmaceuticals was pumped through a short C18 column in such a way that the analytes were retained on the column, whereas polar interferences, eluting at the first of the chromatogram, were discarded to waste. Then, the analytes were transferred by the chromatographic mobile phase to a second C18 analytical column, where they were separated following a conventional chromatography. The optimized approach allowed to preconcentrate 15 mL of sample volume adjusted at acid pH with phosphoric acid and modified with 5% of methanol, at a flow rate of 1.5 mL/min in 10 min. R2 values were between 0.994 and 0.998, detection and quantitation limits ranged between 0.001 and 0.080 and between 0.002 and 0.100 μg/L, respectively, and the interday precision was below 9.8%. Recoveries in three different surface water samples, spiked at concentration levels between 0.002 and 0.500 μg/L (n = 3 for each spiking level), ranged from 82.1 to 125.8% with the relative standard deviation lower than 12%.