The development and study of Microspray and CapillaryElectrophoresisMass Spectrometry Interface

• Main Authors: Chang Yan Zin, 張耀仁
• Other Authors: Her Guor Zone
• Format: Others
• Language: zh-TW
• Published: 2000
• Online Access: http://ndltd.ncl.edu.tw/handle/52052323841466582422

博士 === 國立臺灣大學 === 化學研究所 === 88 === Abstract The combination of capillary electrophoresis (CE) and mass spectrometry (MS) has great potential, as it brings together rapid and highly efficient electrophoretic separations with the selective mass identification and structural elucidation power of MS. Currently, electrospray ionization (ESI) serves as the most common ionization method for CE/MS applications. One major challenge for using ESI-MS as an on-line detector in CE separations is the provision of electrical contact at the capillary outlet. Recently, the development of the use of nanospray interfaces for CE-MS has attracted significant attention. In this paper, we modified an ESI source to the nanospray, and three CE/ESI-MS interfaces based on nanospray was present : the extensive sheath flow interface, the carbon-coated sheathless interface and the micro-sheath flow interface. The most widely used interface for CE/ESI-MS instrumentation is the sheath flow interface but still suffers from poor concentration detection limits relative to LC/MS methods. An extensive sheath flow interface was developed to circumvent this limitation. A piece of metal wire is inserted into sheath flow tube to modify original sheath flow interface. The comparison of sensitivity with the extensive and conventional sheath flow interface of same capillary dimension was studied. An enhancement of approximately 10 times of magnitude in comparison with sheath flow CE/MS. Smith and co-workers introduced the sheathless interface in the initial CE/ESI-MS report. However, the fabrication of sheathless interface requires special equipment and is also time consuming. In addition, the coated tips have a limited lifetime, limiting the routine applications of CE/ESI-MS. A simple procedure was developed for preparing a carbon-coated fused-silica capillary for use in sheathless CE/ESI-MS. The fabrication of a carbon-coated fused-silica capillary tip requires less than 1 min. The stability of this carbon-coated fused-silica capillary is examined, and its utility in on-line sheathless CE/ESI-MS is demonstrated with the separation of berberine, coptisine, and palmatine chlorides. Moreover, a rugged, durable capillary tip with 45° beveling edge was demonstrated a better alternative than a tip with 20 μm orifice often used for sheathless CE/ESI-MS. However, the sheathless interface is not easy to optimize the tip i.d. and the flow rate for CE/ES-MS used non-modified silica capillaries at acid pH values. In addition, the lack of a makeup flow somewhat restricts to use the low surface tension and low conductivity CE buffers which are suitable for electrospray. A micro-sheath flow CE/MS interface that relies on an additional small liquid flow（50∼200 nL/min）by electrosuction was developed to overcome the limitations of the sheathless interface. The sensitivity of micro-sheath flow interface is similar to the sheathless interface and its usefulness is demonstrated with the use of 50 mM ammonium acetate as CE buffers. The use of a dedicated micro-sheath flow interface, which can operate without significant user intervention, allows the routine applications of CE/ESI-MS.