Rapid differentiation of tea products by surface desorption atmospheric pressure chemical ionization mass spectrometry.

Protonated water molecules generated by an ambient corona discharge were directed to impact tea leaves for desorption/ionization at atmospheric pressure. Thus, a novel method based on surface desorption chemical ionization mass spectrometry (DAPCI-MS) has been developed for rapid analysis of tea products without any sample pretreatment. Under the optimized experimental conditions, DAPCI MS spectra of various tea samples are recorded rapidly, and the resulting mass spectra are chemical fingerprints that characterize the tea samples. On the basis of the mass spectral fingerprints, 40 tea samples including green tea, oolong tea, and jasmine tea were successfully differentiated by principal component analysis (PCA) of the mass spectral raw data. The PCA results were also validated with cluster analysis and supervised PCA analysis. The alteration of signal intensity caused by rough surfaces of tea leaves did not cause failure in the separation of the tea products. The experimental findings show that DAPCI-MS creates ions of both volatile and nonvolatile compounds in tea products at atmospheric pressure, providing a practical and convenient tool for high-throughput differentiation of tea products.