Quantitative Determination of Bulk Molecular Concentrations of β‑Agonists in Pork Tissue Samples by Direct Internal Extractive Electrospray Ionization-Mass Spectrometry

Rapid quantitative determination of bulk molecular concentration in solid samples without sample pretreatment is demonstrated using the internal extractive electrospray ionization-mass spectrometry (iEESI-MS) analysis of six β-agonists, including salbutamol (Sal), clenbuterol (Cle), ractopamine (Rac), terbutaline (Ter), tulobuterol (Tul), brombuterol (Bro), in pork tissue samples. Single sample analysis only required 1 min. The linear range of detection was about 0.01–1000 μg/kg (R² > 0.9994). The limit-of-detection (LOD) varied from 0.002 μg/kg for Sal to 0.006 μg/kg for Tul. Relative standard deviation (RSD) of quantitation was in the range 6.5–11.3%. The analytical results were validated by gas chromatography–mass spectrometry (GC–MS) and high-performance liquid chromatography–mass spectrometry (LC–MS), showing the accuracy rates of 92–105%. The current study extends the power of ambient MS as a method for the quantification of molecules at the surface of solid samples (e.g., in μg/cm² units) toward the quantification of molecules in bulk sample volume (i.e., in μg/kg units), which is commonly required in food safety control, biomedical analysis, public security, and many other disciplines.