Luminescent determination of quinolones in milk samples by liquid chromatography/post-column derivatization with terbium oxide nanoparticles

The usefulness of terbium oxide nanoparticles (Tb(4)O(7)NPs) as post-column derivatizing reagent for the liquid chromatographic determination of residues of quinolone antibiotics in milk samples has been studied. Seven quinolones of veterinary use have been chosen as model analytes to develop this method. The derivatization step is based on the formation of luminescent chelates of quinolones with Tb(4)O(7)NPs, which are monitored at lambda(ex) = 340 nm and lambda(em) = 545 nm. Another relevant feature of the method is that the use of a 10-cm column and a ternary mixture of methanol, acetonitrile and acetic acid as mobile phase in gradient elution mode allow the chromatographic separation of the quinolones in about 13 min, whereas previously described chromatographic methods require about 20 min. The dynamic ranges of the calibration graphs and limits of detection are, respectively: 65-900 ng mL(-1) and 35 ng mL(-1) for marbofloxacin, 7.2-900 ngmL(-1) and 2.5 ngmL(-1) for ciprofloxacin, 6-900 ng mL(-1) and 2 ng mL(-1) for danofloxacin, 50-900 ng mL(-1) and 20 ng mL(-1) for enrofloxacin, 35-900 ngmL(-1) and 12 ng mL(-1) for sarafloxacin, 5-900 ngmL(-1) and 2 ngmL(-1) for oxolinic acid, and 7-900 ngmL(-1) and 2.5 ngmL(-1) for flumequine. The precision, established at two concentration levels of each analyte and expressed as the percentage of the relative standard deviation is in the range of 1.9-8.1% using standards, and of 3.4-10.7% in the presence of milk samples. The method has been satisfactorily applied to the analysis of skimmed, semi-skimmed and whole milk samples, with recoveries ranging from 89.0 to 106.5%. (C) 2015 Elsevier B.V. All rights reserved.