Simultaneous determination of 12 β-agonists in feeds by ultra-high-performance liquid chromatography-quadrupole-time-of-flight mass spectrometry.

A new analysis method using ultra-performance liquid chromatography (UPLC)-quadrupole-time-of-flight mass spectrometry (Q/TOF MS) was developed for screening and confirmation of 12 β-agonists in feeds. Under the optimized gradient elution conditions, it takes only 6 min to separate all 12 β-agonists, and the critical pair of Ractopamine and Isoxsuprine isomers was almost completely separated. Based on the over 10,000 full-width at half maximum (FWHM) mass resolution and high mass accuracy features of TOF MS with 20 mDa mass window, accurate mass chromatograms were reconstructed for individual compounds. The fragmentation pathways of 12 β-agonists were also studied using Q-TOF MS. The potential of UPLC-Q/TOF MS for confirmatory analysis was shown by determining the accurate mass of all compounds and fragment ions upon collision-induced-dissociation (CID) at different energies. The extra mass measurement errors for all β-agonists were found to be within 5 ppm. The limits of detection (LODs) and limits of quantitation (LOQs) were determined for all β-agonists in feeds and found to be 1-5 ng/mL and 5-50 μg/kg, respectively. The method of UPLC-Q/TOF MS developed in this study was initially applied to the research of feeds for analysis of 12 β-agonists and proved to be accurate, sensitive, convenient and practical.