Abstract:

β-Agonists, β-blockers, and protein assimilators are classified as stimulant drugs. Their illegal use during animal feeding and slaughtering leads to food-borne stimulant drug residues, which are harmful to human health. At present, methods for the detection of β-agonists and protein assimilators are prevalent, but those for the detection of β-blockers are rare. There is no national standard for the detection of β-blockers in food products of animal origin. A method based on ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was developed for the determination of nine food-borne stimulant drug residues, including β-agonists, β-blockers, and protein assimilators, in pork, egg, and milk. The optimal extraction conditions for this method were as follows: The samples were hydrolyzed with β-glucuronidase/aryl sulfate esterase in pH 5.2 ammonium acetate buffer. Enzymatic hydrolysis was carried out in a constant-temperature (37 ℃) water bath oscillator for 16 h. The enzymolyzed samples were cooled to room temperature and then extracted with acetonitrile, which was adjusted to pH 9.5 with NaOH solution. After extraction and homogeneous mixing, the extract was added to a salt package for salting out stratification. The clear supernatant was cleaned up using an enhanced lipid removal tube (EMR-lipid), which was pre-activated by water. Then, anhydrous magnesium sulfate was added to ensure dehydration of the extract and concentrated to near dryness under nitrogen flow. The residue was dissolved in 1 mL acetonitrile-0.1% formic acid aqueous solution (1∶9, v/v). Separation was performed on an ACQUITY UPLC HSS T3 column (100 mm×2.1 mm, 1.8 μm) with gradient elution using methanol-0.1% formic acid aqueous solution as the mobile phase. The analytes were detected in the multiple reaction monitoring (MRM) mode after being ionized by an electrospray positive ion (ESI⁺). Quantitative analysis was performed by the internal standard method using matrix-matched calibration curves. The effects of the extraction solvent and pH on the extraction efficiency during pretreatment were optimized. The influence factors of different types of chromatographic column, mobile phase and dissolved solution in the process of instrumental analysis were discussed in detail. Under the optimal conditions, the method showed good linearity in the range of 0.5 to 20 μg/L, with correlation coefficients (r²) greater than 0.99. The limits of detection (LODs) and limits of quantification (LOQs) were in the range of 0.3-0.6 μg/kg and 1.0-2.0 μg/kg, respectively. The average recoveries of all the compounds ranged from 65.2% to 117.0% with relative standard deviations (RSDs) in range of 1.3%-14.4% at spiked levels of 1, 2, and 5 times the LOQs. The established method was used to determine the quality of animal-origin foods such as pork, eggs, and milk purchased from the market. The nine stimulant drug residues were not detected in these food samples. The analytical method is rapid, sensitive, accurate, and stable. It can be used for the determination of the nine food-borne stimulant drugs residue in pork, egg, and milk.

Key words: ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS), food-borne stimulant drug, residues, pork, egg, milk