Abstract: A method based on two-step liquid-liquid extraction-solid phase extraction purification coupled with high performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) was developed for the determination of 11 common sulfonamides in pork. The samples were extracted first with ethyl acetate containing 2%(v/v) formic acid and then with acetone for the second step. The supernatant was degreased with n-hexane and cleaned using an Oasis MCX SPE column. Finally, nitrogen was blown over the obtained mixture, and the mixture was filtered for conducting HPLC-MS/MS analysis. The sulfonamides were detected in the multiple reaction monitoring positive ion mode, and quantification was performed by employing the external standard method with matrix calibration curves. All the 11 sulfonamides demonstrated good linearity in the range of 20-400 μg/L, with the correlation coefficient (r²) higher than 0.99. The limits of detection (LODs; S/N=3) and limits of quantification (LOQs; S/N=10) were found to be in the ranges of 0.1-1.0 μg/kg and 0.2-3.0 μg/kg, respectively. Furthermore, the results indicated that the average recoveries of the 11 sulfonamides ranged from 79.3% to 105.5% at three spiked levels of 50, 100, and 200 μg/kg, with the relative standard deviations (RSDs) in the range of 1.3%-11.6% (n=6). This method showed higher extraction efficiency than the one-step liquid-liquid extraction, and the detection sensitivity was highly improved.

Key words: high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS), two-step liquid-liquid extraction, solid phase extraction (SPE), sulfonamides, veterinary drug residues, pork