Fast-screening Chemical Reactions By Low-temperature Plasma Ionization-mass Spectrometry

This dissertation starts with the configuration of mass spectrometry, and focus on the development and application of ionization sources. From the introduction of traditional ionization methods like El, CI, and ESI to recently developed ambient ionization sources, we classify these ambient methods by ionization process and introduce its structure and main application. Among plasma-based ionization sources, LTP (low-temperature plasma) ionization is intriguing and promising for its solvent-free, direct analysis without purification instinct nature. To enhance the selectivity of certain compounds in complex mixtures, a modified version termed as reactive LTP-MS was reported. But due to the geometry restriction of this method, it’s time-consuming and inconvenient to re-load reagents. So we further improve LTP device to implement its application in fast-screening of chemical reactions.In chapter 2,3, and 4 we introduce my main research content. By the construction of several LTP ionization sources, we compare the analysis performance of conventional-LTP device with capillary-LTP device. By employing two sample substrates preloaded with different reagents, we establish reactive LTP-MS method which could detect product of single reaction. Further more, we continue to expand the scope of its application by substituting the fixed substrates with relatively sliding substrates, hence fast-screening of multiple chemical reactions is implemented. The rationale of reactive LTP-MS method is described below:reagent methanol solutions are deposited onto the two sliding substrates in room temperature. By the relative sliding of the two substrates, reagent solutions are sent to the heating region. In the heating region, solvents (methanol) are evaporated and then the reagents are desorbed into atmosphere from substrate surface. In the air, gas phase reagent ions are mixed and collided to generate products. Under the plasma plume, solvent ions, reagent ions as well as corresponding product ions are ionized and detected by mass spectrometry. The reactive LTP-MS method is applied in the identification of products of imine formation, Eschweiler-Clarke methylation, Eberlin reaction. In the fast-screening of chemical reactions,26 out of 28 chemical reactions are successfully screened in a time interval of 30 seconds. Besides,2 transient reactive intermediates are also captured and identified by our reactive LTP-MS method.