Magnetic Metal-Organic Framework/Graphene Oxide-Based Solid-Phase Extraction Combined with Spectrofluorimetry for the Determination of Enrofloxacin in Milk Sample

We have developed an analytical method for the extraction and determination of enrofloxacin in milk sample by magnetic solid-phase extraction with metal-organic framework/graphene oxide (Fe 3 O 4 /MIL-100(Fe)/GO) as a sorbent coupling to spectrofluorimetry. The prepared Fe 3 O 4 /MIL-100(Fe)/GO nanocomposite were characterized by scanning electron microscopy, FT-IR spectroscopy, x-ray diffraction, and vibration sample magnetometer. The parameters affecting extraction efficiency including sample pH, amounts of sorbent, adsorption time, and acidity of elution solvent were optimized systematically. The optimal extraction conditions were as follows: 100.0-mL sample at pH of 8.0, 20.0 mg of Fe 3 O 4 /MIL-100(Fe)/GO as sorbent, extraction time of 30 min, and 4.00 mL of 15% ( v / v ) formic acid in methanol as eluent. A matrix-matched linear relationship (10.00–350.00 μg L −1 ) between the fluorescence intensity and the concentrations of enrofloxacin was obtained with correlation coefficient ( r ) = 0.9979. The limit of detection (S/ N  = 3) and the limit of quantification (S/ N  = 10) were 0.65 and 2.17 μg L −1 , respectively. The relative standard deviations of intraday and interday analysis ( n  = 5) were 1.64 and 2.86%, respectively. The proposed method was successfully applied for the determination of enrofloxacin in milk sample with recoveries ranged from 85.7 to 106.3%.