Rapid Differentiation of Tea Products by Surface Desorption Atmospheric Pressure Chemical Ionization Mass Spectrometry

Abstract

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.

What can we learn from ambient ionization techniques?

“…Obviously, solutions containing a high percentage of organic solvents are not perfectly compatible for in vivo characterization of biological surfaces, especially for diagnosis of patients with allergies. Other techniques such as DAPCI utilize water to efficiently generate the reagent ions [45,46,59,106] and, thus, have been proposed for in vivo characterization of biological surfaces. However, people might be afraid and thus behave abnormally once they see that a "bright fire" (i.e., a high voltage plasma) contacting their skin.…”

Molecular Ionization-Desorption Analysis Source (MIDAS) for Mass Spectrometry: Thin-Layer Chromatography

“…A sheath gas can be used to promote ionization through the introduction of solvents/reagents or, if the gas is heated, through thermal desorption [14,[17][18][19]. Additional DAPCI source descriptions and parameters can be found in a variety of articles [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27]. Examples of applications where DAPCI type sources have been used include hydrocarbons [28], explosives detection [21,29,30], pharmaceuticals [17,24], imaging [31], and natural products [20,23].…”

Analysis of Polycyclic Aromatic Hydrocarbons Using Desorption Atmospheric Pressure Chemical Ionization Coupled to a Portable Mass Spectrometer

“…Desorption atmospheric pressure chemical ionization (DAPCI) is a plasma-based ambient ionization source that is relatively underutilized compared with others [38]. DAPCI has been successfully utilized in the analysis of complex molecules [39], including melamine in powered milk [40], discerning between different variants of Chinese tea [41], analysis of fuels and petroleum oil mixtures [42], explosives, and narcotics [43].…”