A method for the determination of 25 β-receptor agonist residues in milk and dairy products was established based on ultra-high performance liquid chromatography-tandem mass spectrometry. Samples were enzymatically hydrolyzed in 0.2 mol/L ammonium acetate solution at pH 5.2 for 16 h. After the removal of fat and protein through glass fiber filter paper, the filtrate was purified by solid phase extraction (SPE) using a PRiME MCX solid phase extraction column, and separated on a Waters BEH C18 column (100 mm × 2.1 mm, 1.7 μm) by gradient elution using a mobile phase composed of acetonitrile and 0.1% formic acid in water. Mass spectrometry was performed using an electrospray ionization source (ESI) in the positive ion mode with multiple reaction monitoring (MRM), and quantitative determination was performed using the internal standard method. The proposed method showed good linearity for all analytes in the concentration range of 0.2–50.0 ng/mL with coefficients of determination (R2) greater than 0.996; the recoveries ranged from 80.3% to 106.2% with relative standard deviations (RSDs) of 0.6%–8.5% (n = 6). The limits of detection (LOD) were 0.05–0.10 μg/kg, and the limits of quantification (LOQ) were 0.10–0.20 μg/kg. This method is simple, efficient and suitable for the determination of the 25 β-receptor agonist residues in milk and dairy products.

An ultra-high performance liquid chromatography tandem triple quadrupole mass spectrometry (UPLC-MS/MS) method was established for the determination of six quaternary ammonium disinfectant residues in milk-containing food for special medical purposes. The sample was extracted with 80% acetonitrile in water and the extract was separated on a RRHD Eclipse Plus C18 column, detected in the positive ion mode using an electrospray ionization source with multiple reaction monitoring (MRM), and quantified by matrix-matched standard calibration. The calibration curves for the six quaternary ammonium disinfectants was linear in the concentration range of 0.1–5.0 ng/mL with correlation coefficient higher than 0.996 0. The limit of detection (LOD) was 0.5 μg/kg and the limit of quantification (LOQ) was 1 μg/kg. The recoveries were 72.8%-102.3% for spiked solid matrix samples, and 71.8%–100.8% for spiked liquid matrix samples with relative standard deviations (RSDs) in the range of 0.25%–3.88% and 0.19%–2.51%, respectively. The proposed method is simple, efficient, rapid, sensitive, and suitable for the qualitative and quantitative analysis of quaternary ammonium disinfectant residues in food for special medical purposes.