Contactless Carbon Fiber Ionization Mass Spectrometry

• Main Authors: Wu, Min-Li, 吳敏莉
• Other Authors: Chen, Yu-Chie
• Format: Others
• Language: en_US
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/srvx2z

碩士 === 國立交通大學 === 應用化學系碩博士班 === 107 === Many ionization techniques are available in mass spectrometry (MS) for analysis of analytes with different polarities currently. However, most of these developed ionization techniques are only suitable for direct analysis of analytes in either gas or condensed phase. It is rare that an ionization method is suitable for analysis of analytes in both gas and condensed phases. Nevertheless, it is desirable if an ionization technique can be developed for analysis of analytes with different polarities and in different phases. Thus, the main goal of this dissertation is to develop a universal ionization technique that can be used to analyze analytes in gas, liquid, and solid phases. In addition, most of ionization techniques operated in atmospheric pressure require several accessories such as a high voltage-power supply for facilitating ionization processes. This dissertation is also aimed to reduce accessories and to develop a straightforward ionization technique operated in atmospheric pressure. Thus, an ionization method called contactless carbon fiber ionization (CFI)-MS was developed in this study. CFI-MS, in which a bunch of carbon fibers are used as the ionization emitter, has been developed in 2016, but applying electric contact directly on the carbon fiber is required. Herein, the electric contact on the carbon fiber is removed. Thus, we called this developed ionization technique as contactless CFI. Moreover, the previously developed CFI-MS is only suitable for nonpolar or low polarity organics in the low mass region. However, our contactless CFI-MS, in which only a single carbon fiber (diameter: ~10 m; length: 1 cm) is used as the ionization emitter without requiring any electric contact made on the carbon fiber, developed in this study can be used for analysis of analytes with different polarities including non-polar, low polarity, and polar compounds. Furthermore, we demonstrated that the developed ionization technique is suitable for direct analysis of analytes in gas, liquid, and solid phases. Thus, when employing the developed method for direct analysis of sesame oil, the components of the oil with high, low, and high polarities can be directly detected by contactless CFI-MS without any sample pretreatment. In addition, the developed ionization method was further applied to combine with solid phase-microextraction (SPME) by using the CFI-fiber as the SPME adsorbent. Benzo[a]pyrene (BaP), i.e. a known carcinogen, was used as the model sample to demonstrate the feasibility of coupling SPME with CFI-MS. The limit of detection (LOD) toward BaP was as low as ~60 pM, which is lower than the allowed level, ~794 pM, regulated by the United Stated Environmental Protection Agency. Moreover, contactless CFI-MS can be directly used to detect vapor derived from liquid and solid samples that possess high vapor pressure. Pesticides usually possess high vapor pressure at room temperature. Thus, we also employed the developed ionization method for direct analysis of intact tomatoes contaminated by pesticides without conducting any sample pretreatment. Pesticide residues remaining on the surface of an intact tomato can be readily detected by contactless CFI-MS by simply placing the intact tomato in front of the setup of CFI-MS. The LOD of pesticides using this approach is as low as ~5.42×10-6 mg kg-1, which is much lower than the maximum residue level (i.e. 0.01 mg kg-1) of common pesticides regulated by the European Union. Thus, the developed method can be potentially used in rapid screening of the presence of pesticides in intact crops. On the basis of these results, we believe that the developed ionization method should potentially become popular after further studies.