Determination of 14 <italic>β</italic>-agonists in animal meat by ultra high performance liquid chromatography-tandem mass spectrometry

The addition of β-agonists to animal feed can significantly improve the lean-meat rate of pigs, cattle, sheep, and other animals. However, the food residues of β-agonists are harmful to human health. When meat with β-agonist residues is consumed, poisoning symptoms such as palpitation, dizziness, and muscle tremors may develop, and damage to the cardiovascular system, liver, and kidney may occur. In this study, a method based on ultra high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) was established for the rapid detection of 14 β-agonists (clenbuterol, salbutamol, ractopamine, clorprenaline, terbutaline, tulobuterol, bromobuterol, bambuterol, zilpaterol, mabuterol, fenoterol, arformoterol, cimaterol, and cimbuterol) in animal food sources. The sample pretreatment method and chromatographic conditions were optimized. The samples were hydrolyzed with β-glucuronidase hydrochloride/aryl sulfate esterase in ammonium acetate buffer (pH 5.2). Enzymatic hydrolysis was performed in a constant-temperature water bath ((36±2) ℃) oscillator for 16 h. The samples were cooled to room temperature and extracted with 0.5% formic acid acetonitrile. NaCl was added to separate the organic and aqueous phases, and 5 mL of the upper organic layer was purified using a one-step purification solid-phase extraction column. After drying with nitrogen at 50 ℃, the residue was dissolved in 0.4 mL of 0.2% formic acid aqueous solution. The samples were passed through a 0.22 μm filter and detected by UHPLC-MS/MS with gradient elution using acetonitrile and 0.1% formic acid aqueous solution as the mobile phases. The analytes were separated on a Phenomenex Kinetex F5 column and detected by positive-ion scanning in multiple-reaction monitoring (MRM) mode. Internal and external standard methods were used for quantitative analysis. The effects of the extract pH, solid-phase extraction column, purification method, and dissolved solution on the extraction efficiency were optimized during pretreatment. UHPLC-quadrupole time-of-flight MS was used to verify the purification effect of the one-step purification solid-phase extraction column, and the results indicated that this type of column could remove most of the phospholipids, sphingolipids, and glycerides in the sample extract. The factors influencing the different chromatographic columns and mobile phases were investigated. MS scanning was conducted in positive-ion mode with needle pump injection in mass-only mode, and the two daughter ions with the highest responses for each target were selected as the quantitative and qualitative ions. The declustering potential (DP) and collision energy (CE) of each ion were separately optimized in MRM mode. The switching mode of the mass spectrum and waste liquid was used, and the mobile phase was switched to waste liquid after all the target peaks were removed. These steps ensured that impurities in the sample flowed out of the column in a timely manner and that the effects of excessive impurities on the mass spectra were avoided. The 14 β-agonists showed good linear relationships in the range of 1.0-50 μg/L, with correlation coefficients of >0.99. The limits of detection (LODs) and quantification (LOQs) were in the range of 0.1-0.2 and 0.3-0.6 μg/kg, respectively. The average recoveries of the 14 β-agonists ranged from 70.25% to 117.48%, with relative standard deviations (RSDs) in the range of 0.63%-14.29% at low, medium, and high spiked levels. Pork, beef, and mutton samples were selected and analyzed using the developed method. The results were close to those of the national standard method, indicating that the method is accurate and reliable. Moreover, the proposed method has good stability and high accuracy; thus, it is suitable for the qualitative and quantitative determination of β-agonists in animal meat.