Determination of seven non-selective cyclooxygenase inhibitors in milk powder by ultra-performance liquid chromatography-tandem mass spectrometry with dispersive solid phase extraction

An ultra-performance liquid chromatography-tandem mass spectrometry with dispersive solid phase extraction (dSPE-UPLC-MS/MS) method was developed to determine seven non-selective cyclooxygenase inhibitors in milk powder. The samples were extracted with 0.01 mol/L pH 2.5 ascorbic acid-acetonitrile-ethyl acetate solution (2:5:5, v/v/v), and then purified with a mixture of anhydrous sodium sulfate, octadecyl carbon silica gel (C18-N) sorbent and ethylenediamine-N-propyl carbon silica gel (NH2-PSA) sorbent. The analysis was performed using a UPLC-MS/MS system with Waters CORTECS UPLC C18 (100 mm×2.1 mm, 1.6 μm) column. The mobile phase consisted of 0.1% (v/v) formic acid aqueous solution and acetonitrile containing 0.1% (v/v) formic acid by gradient elution, and the multiple reaction monitoring (MRM) mode was used. Five linear calibration curves were obtained with correlation coefficients (r2) ≥ 0.9965. The recoveries were determined at three spiked levels and ranged from 76.4% to 89.8%. The limits of quantification (LOQs) were from 2 to 5 μg/kg. This method is suitable for the determination of seven non-selective cyclooxygenase inhibitors in milk powder.