Determination of eight quinolones in milk using immunoaffinity microextraction in a packed syringe and liquid chromatography with fluorescence detection

We have established a new, highly selective, and sensitive method for the determination of eight quinolones (QNs) in milk: danofloxacin, enrofloxacin, orbifloxacin, norfloxacin, ofloxacin, lomefloxacin, fleroxacin, and ciprofloxacin. The method uses immunoaffinity microextraction in a packed syringe and liquid chromatography with fluorescence detection (IA-MEPS-LC-FLD). Traditionally, QN residues are determined by liquid-liquid extraction (LLE) and solid phase extraction (SPE) sample preparation techniques; however, these methods are time-consuming and require large quantities of organic solvents. We thus developed a novel immunoaffinity adsorbent combined with MEPS for QN residue analysis. The syringe was filled with 0.2 g of microbeads bound with a QN monoclonal antibody using glutaraldehyde. The relevant parameters of the IA-MEPS method were optimized and discussed herein. Milk samples were extracted at a flow rate of 3.5 mL/min, 600 μL of methanol-and phosphate-buffered saline (9:1, v/v) was used for elution, and 200 μL of mobile phase was used for reconstitution after the sample was dried with nitrogen. Then, the sample was detected by LC-FLD. For the eight QNs, the limit of detection ranged from 0.05 to 0.1 ng/g, the limit of quantification ranged from 0.15 to 0.3 ng/g, and the intra- and inter-day precision were 3.2%-14.6% and 9.1%-15.8%, respectively. The advantages of the IA-MEPS method includ simple operation, low cost and reduced organic solvent use. Moreover, the sample pretreatment is environmentally friendly because of the reduced solvent volume requirements.