|| Ambient pressure ionization (API) techniques have accompanied the development of mass spectrometry since the 1970s. Based on the production of ion species, API techniques can be classified as ESI-based or APCI-based. Because multiply-charged analytes can be formed during ESI, ESI/MS can be applied for the detection of polar macromolecules (e.g. proteins and polymers). On the other hand, APCI can be used for the detection of less polar and nonpolar small molecules through ion-molecule reactions and Penning ionization with a mass scan range under 2000 Da. Herein, the development of a coaxial ESI/APCI source with several merits (e.g. small size, simple configuration and easy operation) was introduced. Due to the integration of ESI and DBDI, the coaxial design of the ESI/APCI source can be operated in ESI-only, ESI/APCI and APCI–only modes for characterizing different reactive species (e.g. charged droplets and hydronium ions). Based on sample characteristics, different sampling methods (e.g. laser ablation, laser thermal desorption and ultrasonic nebulization) can be integrated into the developed system for production of neutral intact molecules, fragmented structures and analyte droplets over a wide polarity range. The produced species were then directly ionized via different ionization mechanisms. Similar to other AMS techniques, this system also has short analysis times, quick sample switching and no need for sample pretreatment. The hybrid ionization system can be used for expanding ionization polarities so that multiple sampling systems can be used for analyzing compounds with different characteristics. Finally, an interface was designed that integrated sampling, ionization and chromatographic systems, and operated in different operational modes for rapid chromatographic analysis.|
This study is comprised of six parts; parts I and II discuss different gas phase reactions (e.g. charged reduction mechanisms, proton transfer reactions and fused droplet reactions) using the coaxial ESI/APCI source. Part III combines different sampling methods (nebulization, laser desorption and laser thermal desorption) and ionization systems (ESI and DBDI) to directly analyze samples through direct desorption ionization (direct DI) and two-step ionization. Part IV validates the aforementioned systems for polymer analyses. Part V integrates an aforementioned system with gas chromatography for building a versatile interface that can operate in separation and rapid screening modes. Part VI discusses the development of an analytical system to perform ionization through mechanical force to improve sampling and ionization efficiencies.