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Mass Spectrometric Study of Trace Chemical Analysis, Methanol Electro-Oxidation, and Enzymatic Reaction Kinetics

Cheng, Si
http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1478281433519969

Abstract Details

2016, Doctor of Philosophy (PhD), Ohio University, Chemistry and Biochemistry (Arts and Sciences).
This dissertation introduces the development and applications of liquid sample desorption electrospray ionization mass spectrometry (DESI-MS) for trace analysis of biomolecules and small drugs, monitoring methanol electro-oxidation, and enzymatic reaction kinetics. To enhance the performance of liquid sample DESI, the traditional sample transfer capillary is replaced by a trap column filled with chromatographic stationary phase materials (e.g., C4, C18). This type of trap column/liquid sample DESI can be used for trace analysis of organics and biomolecules (in nM) in high salt containing matrices. Furthermore, when the sample transfer capillary is modified with enzyme covalently bound to its inside capillary wall, fast digestion of proteins such as phosphoproteins (< 6 min) can be achieved, and the online digested proteins can be directly ionized using DESI with high sensitivity. The latter is ascribed to the freedom to select spray solvent for the DESI analysis. Our data shows that liquid sample DESI-MS with a modified sample transfer capillary has expanded its utility in bioanalysis. Another application for DESI-MS is monitoring the methanol oxidation for elucidating the fuel cell reaction and screening the ideal fuel cell electrode material. we present an online ambient mass spectrometric approach for analyzing HCHO generated from methanol electro-oxidation, taking the advantage of high salt tolerance of DESI-MS. It was found that HCHO can be detected as PhNHNH+=CH2 (m/z 121) by DESI after online derivatization with PhNHNH2. With this approach, the analysis of HCHO from methanol electro-oxidation by MS was carried out not only in acidic condition but also in alkaline media for the first time. Efficiencies of different electrodes for methanol oxidation at different pHs were also evaluated. Our results show that the Au electrode produces more HCHO than Pt-based electrodes at alkaline pH while the latter has a higher yield in acidic solution. Enrichment is of great importance for analytical chemistry and forensic chemistry. By using high enrichment efficiency material coupling high-resolution mass spectrometry, it would have significant application potential for abused drug and organic pollutants detection. In this dissertation, two new synthesized materials are introduced. Magnetic graphene framework (MGF) material and magnetic cobalt nanoparticles (Co-NPC) were prepared and used as magnetic solid-phase extraction adsorbent for the preconcentration of flunitrazepam from beverage samples prior to high resolution mass spectrometric determination. The MGF nanocomposite and Co-NPC were characterized by scanning electron microscopy, transmission electron microscopy, vibrating sample magnetometry, and N2 adsorption. The high surface area and specific framework structure of the MGF and magnetic cobalt nanoparticles endow them with a high adsorption capacity. Several experimental parameters affecting the extraction efficiencies, such as the amount of the adsorbent, extraction time, sample pH, salt addition and desorption conditions were optimized. Under the optimum conditions, the MGF and magnetic cobalt nanoparticles adsorbent would have a significant application potential for the enrichment of other abused drug and organic pollutants in different samples. Kinetic studies play an essential role in the elucidation of chemical and biochemical reaction mechanisms. By using DESI-MS, enzymatic reaction products in buffered aqueous solution (e.g., tris buffer) could be directly detected. Furthermore, by adjusting the pH and solvent composition of the DESI spray, the reaction can be quenched online to avoid post-ionization reactions, leading to the fast and accurate measurement of kinetic constants. Reaction time control can be obtained simply by adjusting enzyme and substrate solution injection flow rates. Enzymatic reactions examined in this study include hydrolysis of 2-nitrophenyl-ß-D-galactopyranoside by ß-galactosidase and hydrolysis of acetylcholine by acetylcholinesterase. Derived Michaelis–Menten constants Km for these two reactions were determined to be 328.6 µM and 0.27 mM, respectively, which are in excellent agreement with 330 µM and 0.23 mM reported in the literature, validating the DESI-MS approach. In addition, this time-resolved DESI-MS also allowed us to determine Km and turnover number kcat for trypsin digestion reaction, for the first time (Km and kcat are 7.5 mM and 1.7 s-1, respectively, for the substrate Angiotensin II)
Hao Chen (Advisor)
129 p.
Analytical Chemistry; Chemistry
mass spectrometry; liquid sample desorption electrospray ionizaiton; enrichment; electrochemistry; enzymatic reaction kinetics

Recommended Citations

Citations

  • Cheng, S. (2016). Mass Spectrometric Study of Trace Chemical Analysis, Methanol Electro-Oxidation, and Enzymatic Reaction Kinetics [Doctoral dissertation, Ohio University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1478281433519969

    APA Style (7th edition)

  • Cheng, Si. Mass Spectrometric Study of Trace Chemical Analysis, Methanol Electro-Oxidation, and Enzymatic Reaction Kinetics . 2016. Ohio University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1478281433519969.

    MLA Style (8th edition)

  • Cheng, Si. "Mass Spectrometric Study of Trace Chemical Analysis, Methanol Electro-Oxidation, and Enzymatic Reaction Kinetics ." Doctoral dissertation, Ohio University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1478281433519969

    Chicago Manual of Style (17th edition)

ohiou1478281433519969
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This open access ETD is published by Ohio University and OhioLINK.