ELECTRON MONOCHROMATOR TIME-OF-FIGHT MASS SPECTROMETER

在负离子的产生过程中，低能电子与亲电分子的相互作用是一个重要的化学过程。电子捕获负离子质谱仪(ECNI-MS)是一种用于分析极少量此类化合物的强大系统，但在目前的形式下，它只能提供有关产生负离子的过程的有限信息。在这一应用中，我们建议构建一种通用的气相色谱/电子单色器飞行时间质谱仪(GC/EM-TOF-MS)。该仪器将用于阐明通过亚稳态离子形成和分解负离子的机制。将使用的电子单色器(EM)产生单能电子束，其电流约为400微安，在0-15 eV范围内可调，最大能散为O.lev。当电子源与飞行时间(TOF)分析器连接时，将产生可重现的三维光谱，其轴是共振电子能量、带电质量和离子信号强度。气相色谱进样系统将提供一种分解化合物混合物的手段和稳定的缓冲气体供应，以稳定共振电子捕获离子。分析器中的反射器将提供研究亚稳态离子的能力。当实验共振电子能与密度泛函理论方法计算的分子的虚拟轨道能相关联时，将提供有关初始离子形成过程中所涉及的轨道的信息。将研究几类亲电化合物的电子附着性，包括有机磷、磺酰胺、二硝基[2，2]对环番、脂肪酮、卤代乙烯、氯乙烯和氯乙醛。除了为研究负离子形成的机理细节提供一个独特的系统外，拟议的GC/EM-TOF MS仪器的灵敏度、特异性、来自共振电子能量的额外分析信息以及“快速”的GC/MS能力将使其成为分析与环境健康相关的化学品、生化和生物医学相关化合物的宝贵新工具。GC/EM-TOF-MS系统的另一个潜在的令人兴奋的应用是对蛋白质、多肽和其他具有电子捕获翻译后修饰的生物聚合物的分析。

The interaction of low-energy electrons with electrophilic molecules in the production of negative ions is an important chemical process. Electron capture negative ion mass spectrometry (ECNI-MS) is a powerful system used for the analysis of very small amounts of such compounds, but in its present forms it can provide only limited information on the processes that produce negative ions. In this application we propose to construct a versatile gas chromatography/electron monochromator-time-of- flight mass spectrometer (GC/EM-TOF-MS). This instrument will be used to elucidate mechanisms of negative ion formation and decomposition via metastable ions. The electron monochromator (EM) to be used generates monoenergetic electron beams with currents of approximately 400 microamps tunable in the range 0- 15eV with maximum energy spreads of O.leV. The electron source when interfaced to the time-of-flight (TOF) analyzer will yield reproducible 3-dimensional spectra whose axes are resonance electron energy mass to charge, and ion signal intensity. The gas chromatographici nlet system, will provide a means to resolve compound mixtures and a stable supply of buffer gas to stabilize resonance electron capture ions. A reflectron in the analyzer will provide the capability to study metastable ions. Experimental resonance electron energies, when correlated with the virtual orbital energies of the molecules calculated by density functional theory methods, will provide information on the orbitals involved during initial ion formation. Electron attachment to several classes of electrophilic compounds including organophosphates, sulfonamides, dinitro [2,2]para- cyclophane, aliphatic ketones, haloethenes, vinyl chloride and chloroacetaldehyde will be investigated. In addition to providing a unique system for studying the mechanistic details of negative ion formation, the sensitivity, specificity, extra dimension of analytical information from resonance electron energies and "fast" GC/MS capability of the proposed GC/EM-TOF MS instrument will make it a valuable new tool for analyzing environmental health-related chemicals, biochemical and biomedical-related compounds that can be derivatized with electrophores. The analysis of proteins, peptides and other biopolymers with electron-capturing posttranslational modifications is another potentially exciting application for the GC/EM-TOF-MS system.