Abstract:

In the aquaculture industry, fluoroquinolones are widely used as effective therapeutic agents to prevent animal diseases. The wide bactericidal activity of fluoroquinolones strongly depends on their concentration. Abuse of fluoroquinolones is considered the main reason for the possible occurrence of residues in aquatic products. The increasing presence of residues in aquatic products may pose potential risks to human health. Therefore, it is important to develop an efficient, sensitive, and reliable method for the simultaneous determination of fluoroquinolones in aquatic products. In the analysis of fluoroquinolones, many HPLC methods with different detection techniques have been applied. Among the most common used techniques, HPLC-MS is possible for the determination of very low level analytes in matrix. For the determination of low concentrations of fluoroquinolone residues in aquatic products, preliminary extraction and purification steps are frequently needed to achieve low detection limits. Accelerated solvent extraction (ASE) is well suited for the determination of organic pollutants in solid samples. ASE has the advantages of a high degree of automation, sufficient extraction, high speed, and less solvent consumption, but it has the disadvantage of poor purification effects. Magnetic solid-phase extraction (MSPE) has attracted considerable attention on account of its benefits such as easy separation, less solvent consumption, and quick adsorption of antibiotic residues in liquid samples. The combination of ASE with MSPE makes it possible to sufficiently extract and further purify the target compounds from complex solid samples. Compared with the currently used purification methods of SPE and QuECHERS, MSPE has advantages such as no need of centrifugation and filtration, less solvent consumption, and low cost by appropriate choice of magnetic materials. In this study, a method based on ASE-MSPE-HPLC-MS/MS was developed for the simultaneous determination of sarafloxacin, ofloxacin, enrofloxacin, danofloxacin, lomefloxacin, pefloxacin, ciprofloxacin, enoxacin, norfloxacin, and difloxacin in yellow croaker, grass carp, black fish, prawn, and macrobrachium. As a magnetic purification sorbent, a graphene oxide nanoscale-coated zerovalent iron adsorbent composite (GO@nZVI), was facilely prepared at room temperature. GO and nZVI solutions were rapidly vortex-mixed at 25 ℃, and then, the magnetite precipitate was magnetically isolated to obtain GO@nZVI. Simpler than the usually used preparation methods, GO@nZVI can be fabricated without complicated multi-step synthesis, fussy operation and harsh conditions. nZVI nanomaterials have strong multiple interactions (hydrogen bonding, electrostatic interaction or their combination) with GO composite only with appropriate adjustment of pH values. The synthesized magnetic purification sorbents were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, and X-ray diffraction (XRD), indicating the successful formation of GO@nZVI. The magnetic material was used to purify and extract ten fluoroquinolone residues in aquatic products via MSPE, followed by ASE. In ASE step, the analytes were extracted from the aquatic products using methanol for 5 min at 70 ℃, under an extractive pressure of 10.34 MPa for three cycles. The extract was purified by MSPE using GO@nZVI. The target compounds were separated on an Agilent ZORBAX Eclipse Plus C18 column (100 mm×3.0 mm, 1.8 μm) with gradient elution, and analyzed in multiple reaction monitoring (MRM) mode with positive electrospray ionization (ESI⁺). Under the optimized conditions, good linearities were obtained for the ten fluoroquinolones in the range of 1-100 μg/kg, with correlation coefficients above 0.99. LODs (S/N=3) and LOQs (S/N=10) were 0.02-0.29 μg/kg and 0.07-0.98 μg/kg, respectively. At three spiked levels, the recoveries of the fluoroquinolones were between 81.6% and 105.8%, with RSDs between 4.2% and 13.6%. Overall, the major advantages of this combined ASE-MSPE-HPLC-MS/MS method are facile preparation of the magnetic purification material, automated and simple operation, high sensitivity, short extraction time, and less solvent consumption. This sensitive, repetitive method could be successfully employed for the determination of ten fluoroquinolone residues in aquatic products, with good recoveries.

Key words: accelerated solvent extraction (ASE), magnetic solid-phase extraction (MSPE), high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS), fluoroquinolones, aquatic products