Simultaneous Determination of Residues of 12 Phenothiazines in Pig Hair by Ultra-High Performance Liquid Chromatography-Tandem High Resolution Mass Spectrometry

Considering the hair sample had advantages of convenient sampling and simple pre-treatment, which can achieve continuous dynamic monitoring of prohibited drugs in animal derived agricultural products, the study mentioned by the title was conducted. The pig hair sample was forzen at −40 ℃, cleaned, blown to dryness by nitrogen, cuted into small pieces, and placed into a liquid nitrogen freezer grinder, of which the frequency of collision oscillation was set to 12 times·s⁻¹, milling time was set to 3.5 min, and stabilization time was set to 5 min. The sample was ground into powder, an aliquot (80 mg) was taken, and 4 μL of 1 000 μg·L⁻¹ mixed internal standard solution and 10 mL of acetonitrile solution containing 0.1% (volume fraction, the same below) formic acid were added. The mixture was ultrasonicated for 5 min, and centrifuged at 4 ℃ for 3 min. The supernatant was filtered by a 0.45 μm filter membrane, and all the filtrate was passed through the Oasis PRIME HLB solid phase extraction column. The effluent was collected, and an aliquot (5 mL) was taken, and blown to dyrness by nitrogen at 60 ℃. Then 200 μL of methanol was added for dissolution, and the solution obtained was centrifuged at 4 ℃ for 1 min. The supernatant was determined according to the optimized instrument working conditions. In chromatographic analysis, gradient elution separation was performed using Waters Acquity BEH C₁₈ column as the stationary phase, and mixed solutions composed of 0.1% formic acid solution and methanol at different volume ratios as the mobile phase. In the tandem mass spectrometry analysis, the positive ion mode of the heated electrospray ion source was used for ionization, the peak area of the parent ion was used for internal standard quantification, and the precise mass number of the daughter ion was used for qualitative analysis. It was shown that linear relationships between values of the mass concentration and the peak area ratio were kept in the range of 1－200 μg·L⁻¹ for chlorpromazine, chlorpromazine sulfoxide, promethazine, propionyl promethazine, thiolidazine, trifluoperazine and 2－200 μg·L⁻¹ for promethazine sulfoxide, methylthiazide, acetylpromethazine, perphenazine, fluphenazine, decafluphenazine, with detection limits (3S/N) in the range of 2－4 μg·kg⁻¹. Test for recovery was made according to the standard addition method, giving recoveries in the range of 84.6%－107%, and RSDs (n=5) of the determined values ranged from 1.2% to 13%.