Fluorescent labelling of ciprofloxacin and norfloxacin and its application for residues analysis in surface water

•A simple and inexpensive fluorescent labelling protocol of fluoroquinolones were developed.•Sample clean-up by HLB and FQ-MIP greatly removed matrices and enhanced percent recoveries.•The validated LC-fluorescence was applied to analysis of fluoroquinolone residues in water.•The method would be compatible to miniaturized systems equipped with UV-visible detectors.

Sensitivity enhancement for residue analysis of ciprofloxacin and norfloxacin in surface water was performed by liquid chromatography with fluorescent detection (LC-FD). Labelling of both drugs were studied with fluorescent probes (e.g. Nile blue perchlorate (NBP) and 4- (N,N-Dimethylaminosulfonyl)-7-(N-chloroformylmethyl-N-methylamino)-2,1,3-benzoxadiazole (DBD-COCl). Factors affecting the derivatization (e.g. stoichiometric ratios, reaction time and base catalysts) were optimized. The derivatization was achieved in 15 min using a stoichiometric ratio between the substrate and DBD-COCl of 1:3, whereas NBP gave unsatisfactory results. Separation of the derivatives by LC was achieved (resolution (RS) > 1.8) on a C8 column using a mobile phase consisting of 50 mM formic acid and acetonitrile (ACN) (68:32% v/v) in 20 min. The method was linear (r2 > 0.99) in a range of 200–2,000 µg/L, precise (%RSD < 9.17) and accurate (%recovery of 102.5–122.2%) for the determination of the derivatives. The uses of fluoroquinolone molecularly imprinted polymer in conjunction with hydrophilic-lipophilic balance sorbents demonstrated an efficient procedure for sample pre-concentration and clean-up for water sample resulting in the improved percent recovery. Applications of the proposed method was shown in surface water samples in Thailand.

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