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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 (R > 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/cm 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.

Human sputum, a typical highly viscous biosample, was directly characterized at the molecular level using neutral desorption extractive electrospray ionization mass spectrometry (ND-EESI-MS) without multi-step sample pretreatment, in an attempt to provide a method for constructing the pattern recognition of rapid diagnosis of lung cancer. Under the optimal experiment conditions, glucose, amino acids, phosphoric lipids and other typical analytes in the sputum sample could be used to conduct qualitative or quantitative (in arginine) analysis. More interestingly, the full scan mass spectra from 50 patients of non-small cell lung cancer, recording the mass spectral fingerprints of sputum samples, were differentiated from the control group (50 healthy individuals) through principal component analysis (PCA). These findings suggest that valuable molecular information concealed in human sputum could be easily revealed and applied for conducting qualitative or quantitative analysis by direct ND-EESI-MS analysis.

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Direct mass spectrometry analysis of metabolic effects of clenbuterol and salbutamol on pork quality at the molecular level is incredibly beneficial for food regulations, public health and the development of new anti-obesity drugs. With internal extractive electrospray ionization mass spectrometry (iEESI-MS), nutrients including creatine, amino acids, L-carnitine, vitamin B6, carnosine and phosphatidylcholines in pork tissue were identified, without sample pretreatment, using collision-induced dissociation (CID) experiments and by comparison with authentic compounds. Furthermore, normal pork samples were clearly differentiated from pork samples with clenbuterol and salbutamol via principal component analysis (PCA). Correlation analysis performed on the spectral data revealed that the above-mentioned nutrients strongly correlated with pork quality, and the absolute intensity of phosphatidylcholines in normal pork was much higher than pork contaminated by clenbuterol and salbutamol. Our findings suggested that clenbuterol and salbutamol may render effects on the activity of carnitine acyltransferase I, hence the process that L-carnitine transports long-chain fatty acids into mitochondria and the formation of phosphatidylcholines might be affected. However, the underlying metabolic mechanisms of clenbuterol and salbutamol on carnitine acyltransferase I requires more comprehensive studies in future work.