Real-time mass spectrometric monitoring of chemical processes

Date

2021-01-05

Authors

Omari, Isaac Obeng

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Abstract

Reactions can be monitored in real-time or off-line for qualitative and quantitative information on reaction systems under study. The work presented in this dissertation was focused on the application of reaction monitoring techniques by means of electrospray ionization mass spectrometry (ESI-MS), and ultraviolet-visible (UV-Vis) spectroscopy to solve various problems. For example, in a complex petroleum matrix, naphthenic acids were selectively derivatized using a charge-tagging technique and all the acid derivatives were identified by tandem electrospray ionization mass spectrometry (ESI-MS/MS). To understand the increased visibility of analytes profiled with charge-tagged reagents in ESI-MS, ESI response of permanently charged analytes of different sizes and structures were examined. It turned out that factors, such as the analyte structure, molecular weight and solvent could influence the signal strength of analytes. In a separate study on the effect of magnesium (Mg2+) on Maillard reaction, ESI-MS was used to characterize reaction species, and it was found through UV-Vis spectroscopy that, magnesium can accelerate Maillard chemistry in a dose-dependent manner. ESI-MS was also employed to investigate hydrolysis of aryltrifluoroborates in real-time complemented by pH analysis, whereby a dynamic series of equilibria for numerous ions was determined. As well, by using ESI-MS for on-line reaction monitoring, reaction intermediates of a palladium-catalyzed cyclization reaction of carbamates, and an acid-catalyzed cyclization reaction of benzoxazine were identified. Furthermore, to ensure uniform stirring in reactions conducted simultaneously, a 3D printed circular vial holder enabled standardized stirring conditions in ten vials; and ESI-MS revealed data reproducibility could be achieved through the standardized stirring conditions offered by the vial holder. In a nutshell, the findings given provide practical considerations, and some insights into fundamental ESI-MS science.

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Keywords

mass spectrometry, real-time analysis, reaction monitoring, small-scale surveys, charge-tagging, response factor, catalysis

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