Preconcentration of some fluoroquinolone antibiotics by magnetic solid-phase extraction using magnetite nanoparticles

Abstract

Polyethylenimine (PEI)-modified superparamagnetic magnetite nanoparticles (MNP) were prepared by co-precipitation method and applied for magnetic solid-phase extraction (MSPE) of three fluoroquino- lones (enrofloxacin (EF), levofloxacin (LF), pefloxacin (PF)) from water samples. Monodispersed MNP were synthesized at a PEI concentration of 2 wt% and  characterized  by  transmission  electron  microscopy  (10±2 нм). The electrostatic adsorption of PEI was allowed to proceed for 15 min under mechanical agita- tion, then the excess of cationic polyelectrolyte, which did not electrostatically adsorb on the MNP, was re- moved by magnetic separation/wash/re-dispersion three times cycles by permanent magnet. It was found that ζ-the potential of PEI coated nanoparticles is maximal at a pH of 3-4, and at pH 3.2 it is equal to +35 mV. The effect of various experimental factors such as the method (mechanical or ultrasound agitation) and time of establishing the sorption equilibrium, the pH of solution, the quantity of the MNP, the influence of antibi- otic concentration, the contact time and the temperature sample were studied using the batch technique. The concentration of unbound antibiotic in the sorption equilibrium was determined from calibration curve using native fluorescence of EF, LF and Tb(III)-PF chelate fluorescence. With enrofloxacin as an example, it has been established that sorption is characterized by the Langmuir model. The sorption isotherm testifies to the high affinity of PEI-modified MNP to fluoroquinolones. Preconcentration on a sorbent with a mass of 18 mg under the of ultrasound agitation during 15 min with a degree of extraction ³ 90% is possible from solutions of fluoroquinolones with a concentration of up to 1·10^{-5 M} in a volume of 50 ml and the adsorption capacity of antibiotics in this case increases to 180-200 mg g^{− 1} of magnetite. The degree of extraction of all three antibiotics from 50 ml at optimal pH 3.2-3.3 using 18 mg of magnetite and fluoroquinolone concentration 2·10^{-6 M was 97}±2%, the preconcentration coefficient changes in the range (2.4-2.8)·10³. By increasing the volume of the antibiotic solution to 150-250 ml, the preconcentration coefficient increases to (5.5-5.7)·10³.