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

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 (R_S) > 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.