Determination of Florfenicol Enantiomers and Their Metabolite Florfenicol Amine in Pork by Ultra-Performance Convergence Chromatography with Solid Phase Extraction

Ethyl acetate solution (25 mL) containing 3% (φ) aqueous ammonia was added into 10.0 g of pork sample, the mixture was vortexed for 1 min, centrifuged for 5 min, and the precipitation was extracted once again as the method described above. The two extracts were combined and evaporated to nearly dry under vacuum at 40℃, and the residue was redissolved with 10 mL of phosphate buffer solution (pH 6.0). The HLB solid phase column activated beforehand was used for loading the solution, washed with 10 mL of water, drained by vacuum for 1 min, and eluted with 6 mL of methanol. The eluate was collected and dried by nitrogen at 40℃ to nearly dry. The residue was dissolved by vortex for 3 min with 1 mL of mixed solution of n-heptane and isopropanol at volume ratio of 8:2, filtered through a 0.22 μm filter membrane and the filtrate was analyzed by ultra-performance convergence chromatography. CHIRALPAK AD-3 chiral column was used as the stationary phase with column temperature of 40℃ and the system back pressure of 13.8 MPa. The mixture of supercritical carbon dioxide and methanol solution containing 0.5% (φ) aqueous ammonia at different volume ratios was used as the mobile phase for gradient elution. (-)-Florfenicol, (+)-florfenicol and their metabolite florfenicol amine were determined by external standard method at wavelength of 224 nm. It was shown that the mass concentrations of the 3 targets were linearly related with their corresponding peak areas in the range of 0.50-20.00 mg·L^-1, and the lower limits of determination were 0.05 mg·kg^-1for (-)-florfenicol and (+)-florfenicol and 0.1 mg·kg^-1 (for florfenicol amine). Test for the spiked recovery was made on the negative pork samples at the 3 concentration levels, giving recoveries of the 3 targets in the range of 81.2%-107%, and RSDs (n=6) of the determined values ranged from 5.0% to 9.0%. The proposed method was used for the analysis of 20 pork samples, and (-)-florfenicol (248 μg·kg^-1) was detected in one sample.