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Coupling Ambient Ionization Mass Spectrometry with Liquid Chromatography and Electrochemistry and Their Applications

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2016, Doctor of Philosophy (PhD), Ohio University, Chemistry and Biochemistry (Arts and Sciences).
Ambient ionization methods allow the ionization of untreated samples in the open environment. In this dissertation, two different ambient ionization techniques, desorption electrospray ionization (DESI) and probe electrospray ionization (PESI), has been developed and coupled with liquid chromatograph (LC) and electrochemistry (EC) and their analytical applications have been explored and discussed. Liquid sample DESI generally employs a DESI probe to spray solvent with high voltage to ionize sample as the sample solution is delivered to the ion source by a piece of fused silica transfer capillary. A new splitting interface, a PEEK capillary tube with a micro-orifice drilled in the capillary wall, was used to connect with LC column for applying DESI ionization. A small portion of LC eluent emerging from the orifice can be directly ionized by DESI with negligible time delay while the remaining analytes can be online collected. Furthermore, online derivatization using reactive DESI is possible for additional application such as supercharging proteins. Since splitting via an orifice introduces negligible dead volume and back pressure, the performance of the LC/DESI-MS with the focus of using ultra-fast LC for analyzing sample was further evaluated. Using a monolithic C18 column, metabolites in urine can be separated within 1.6 min, online monitored by DESI and collected as purified samples. Negative ions can be directly generated for acidic analytes in acidic LC eluent by DESI during the LC/MS analysis process using a spray solvent with alkaline pH. In addition, DESI-MS is found to be compatible with ultra-performance liquid chromatography (UPLC) for the first time. The 45 s separation of drugs can be achieved via UPLC/DESI-MS under high temperature. The combination with EC further broadens LC/MS applications. UPLC-MS combined with EC via DESI was first developed for the structural analysis of proteins/peptides that contain disulfide bonds. Using this combined UPLC/EC/DESI-MS method, peptides containing disulfide bonds can be differentiated from those without disulfide bonds, as the former are electroactive and reducible. MS/MS analysis of disulfide-reduced peptide ions provides increased information about the peptide sequence and disulfide-linkage pattern. In addition, upon online electrolytic reduction and reactive DESI, supercharged proteins showed increased charges distribution which is of value for MS/MS sequencing application. PESI, another ambient ionization technique, employs a conductive solid probe to ionize samples directly on the probe tip with the aid of applied high voltage. Due to the high salt tolerance of PESI, the detection of electrochemical reaction products in room-temperature ionic liquids is realized, for the first time. Furthermore, PESI-MS allows the detection the electrochemical reaction products on different or multiple electrode surfaces. In addition, peptides and proteins fractionated through isoelectric focusing (IEF) can also be directly analyzed by PESI-MS.
Hao Chen (Advisor)
Peter Harrington (Committee Member)
Shiyong Wu (Committee Member)
Shigeru Okada (Committee Member)
130 p.

Recommended Citations

Citations

  • Cai, Y. (2016). Coupling Ambient Ionization Mass Spectrometry with Liquid Chromatography and Electrochemistry and Their Applications [Doctoral dissertation, Ohio University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1472816263

    APA Style (7th edition)

  • Cai, Yi. Coupling Ambient Ionization Mass Spectrometry with Liquid Chromatography and Electrochemistry and Their Applications. 2016. Ohio University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1472816263.

    MLA Style (8th edition)

  • Cai, Yi. "Coupling Ambient Ionization Mass Spectrometry with Liquid Chromatography and Electrochemistry and Their Applications." Doctoral dissertation, Ohio University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1472816263

    Chicago Manual of Style (17th edition)