| β-agonists are a kind of phenethylamines ramification with structure and function similar to adrenaline. In this paper a method was developed for simultaneous determination of four β-agonists by gas chromatography/mass spectrometry (GC/MS) in pork tissues. The homogenized samples were enzyme digested by β-glucuronidase enzyme, and extracted with 20mmol/L ammonium acetate. Further cleanup was performed on a MCX cartridge and the purified drugs were evaporated to dryness with nitrogen fluent. Residue must be dry before adding Sylon BFT[BSTFA+TMCS, 99+1(v/v)]. Add 100 μL Sylon BFT to cuvette, mixed briefly with vortex mixer, avoid light, heated 1h at 70℃. After derivatization, the solution was evaporated to dryness with nitrogen gas. Toluene was added directly to the sample, and shook on vortex mixer for 30sec.Then analytes were determined and confirmed by gas chromatography/mass spectrometry (GC/MS), analyzed by electron ionization with selected ion monitoring (SIM) mode. The ions were chosen respectively for the monitoring at m/z 86, 187,212, 262 for clenbuterol, m/z86 was m/z 376, 378, 466, 468 for salbutamol, m/z 86, 336, 356, 357 for terbutaline and m/z 236, 322, 356, 412 for fenoterol. Quantitative ions were selected at m/z86 for clenbuterol, m/z369 for salbutamol, m/z356 for terbutaline and m/z322 for fenoterol. The recoveries of clenbuterol at the fortified lever of 5 μg/kg, 10 μg/kg, 50μg/kg ranged from 88.51%~103.90%, salbutamol at the fortified lever of 5 μg/kg, 10 μg/kg, 50 μg/kg ranged from 82.26%~107.00%, terbutaline at the fortified lever of 5 μg/kg, 10 μg/kg, 50 μg/kg ranged from 95.57%~107.80%, fenoterol at the fortified lever of 5 μg/kg, 10 μg/kg, 50 μg/kg ranged from 68.46%~107.10%, respectively. Coefficents of variation for distribution (CV_d) of clenbuterol, ranged from 2.0%~4.5%, salbutamol ranged from 2.1%~4.4%, terbutaline ranged from1.9%~3.2%, fenoterol ranged from 2.9%~4.3% respectively. And for precision CV_r, ranged from 2.1%~12.7% for clenbuterol, 2.7%~8.0% for salbutamol, 3.0%~12.1% for terbutaline, 2.9%~10.5% for fenoterol, respectively. The limit of detection (LOD) is 0.5 μg/kg for clentuterol and salbutamol, 1.7 μg/kg for terbutaline and fenoterol, respectively.In order to reinforce the execution and to improve the efficiency of monitoring of violation of prohibited drugs, it is required to have a method with better performance, especially with lower detection limit. As described in literature, large volume injection method is capable of reducing LOD, improving sensitivity, decreasing workload of the sample treating, and therefore to get advanced work efficiency. This paper, using large volume injection method, succeeded reducing LOD and improving sensitivity. The LOD is 0.05 μg/kg for clentuterol and salbutamol, 0.17 μg/kg for terbutaline and fenoterol, respectively.The assessment of uncertainty of a test method is the basic requirments of ISO/IEC- 17025standard. It is also the need of mutual recognition in international practise. In this paper, we have assessed the standard uncertainty, combined standard uncertainty, freedom and expanded uncertainty to the method of determination of p-agonist residues in pork by solid-phase extraction and gas chromatography/Mass spectrometry.
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