可快速切换VUV电离和射频增强的化学电离源及其在C2-C12碳氢化合物在线质谱测量中的应用

Single-photon ionization (SPI) with vacuum ultraviolet (VUV) light is a kind of soft ionization source for mass spectrometry, and it is characterized by its high molecular ion yield and very low degree of fragmentation. The sensitivity of SPI for C2-C12 hydrocarbons,especially short-chain saturated alkanes,is pretty low, due to its low photoionization cross-section and the low light density with commercial VUV lamp. This project aims to develop a new soft ionization source that combines SPI with radio frequency field enhanced chemical ionization (SPI/CI) to achieve high sensitivity and wide application scopes. A rf voltage was coupled to the second electrode of the ionization source, and photoelectrons generated by VUV photon oscillated in rf field. In the process of oscillation, photoelectrons were accelerated to ionize reactant gas oxygen and consequently charge exchange chemical ionization was achieved through ion-molecule reaction with O2+. The oscillation of O2+ in the radical direction of ionization source with rf field extended its motion path and collisions between reactant ion and analyte molecules, and consequently improved the ionization efficiency. Experimental parameters of ionization source, ion funnel and ion lens will be optimized by SIMION theoretical simulation in order to improve the ion utility, and integration of ion funnel with chemical ionization source will also be explored. The combined SPI-CI source with on-line ion trap mass spectrometer or time-of-flight mass spectrometer will be used to develop a rapid analytical method for C2-C12 hydrocarbons concentration and composition analysis. This method facilitates with auto quantitative analysis calibration, rapid switching between SPI and SPI-CI. The combined SPI-CI source ion trap mass spectrometer also has great potential for online monitoring of other volatile organic compounds in complex samples, and it promises to be used as a platform for on-line rapid analysis.

真空紫外（VUV）灯单光子电离（SPI）是一种质谱软电离源，其电离样品得到分子离子峰，谱图简单便于解析。C2-C12碳氢化合物特别短链饱和烷烃由于光电离截面小、VUV灯光密度低其SPI电离灵敏度差。本项目拟设计可快速切换VUV单光子和射频增强的化学电离复合离子源解决这一问题。以射频电场调制光电效应得到的光电子电离空气中的O2，以O2+作为CI试剂离子通过电荷转移实现样品电离；电离区中以射频电场增加O2+的运动路径、停留时间以提高其与样品碰撞次数进而增强电离效率；探索化学电离区与具有离子聚焦性能的离子漏斗联合，通过SIMION模拟离子运动轨迹，优化CI电离区、离子漏斗区域的电场参数，设计一体化的电离区-离子漏斗，提高样品离子的利用率；通过SPI/SPI-CI电离模式切换、试剂离子变换，结合在线离子阱或者飞行时间质谱实现复杂基质中C2-C12碳氢化合物特别是短链饱和烷烃在线浓度和组成快速分析。

真空紫外（VUV）灯单光子电离（SPI）仅得到样品分子离子峰，是一种质谱软电离源，谱图简单便于解析，但VUV-SPI存在光通量小、电离范围限于电离能小于10.6 eV化合物缺点。C2-C12 碳氢化合物特别短链饱和烷烃由于光电离截面小、VUV 灯光密度低其 SPI 电离灵敏度差。本项目基于VUV灯设计了可快速切换单光子电离/射频增强的化学电离复合离子源有效解决了C2-C12检测灵敏度问题。项目中先后以射频电场作为辅助，设计了单电极、多电极聚焦化学电离源，以射频电场调制光电效应得到的光电子电离空气中的 O2，以 O2+作为化学电离试剂离子通过电荷转移实现样品电离，仪器灵敏度提高70多倍，并且通过理论模拟解释了射频电场有效增强化学电离碰撞次数从而提高灵敏度的机理。项目针对VUV光衰减，设计了一种在线自动校正程序，自动调节试剂离子O2+的强度，基于该方法进行了催化合成氨反应产物NH3的实时定量，利用该校正程序O2+和NH3+强度值的定量相对标准偏差RSDs分别为0.38%和1.3%，实现了高效定量。为了提高仪器在大气环境中C2-C12的检测灵敏度，项目中还研制了冷阱在线富集仪，经过冷阱富集后，仪器灵敏度提高至少200倍以上，对于C2的氯乙烷检测限达到了0.003 μg/m³的高灵敏度。通过 SPI/SPI-CI 电离模式切换、试剂离子变换，结合在线飞行时间质谱实现EPA TO-14/TO-15中规定的多种 C2-C12 碳氢化合物特别是短链饱和烷烃在线快速、高灵敏分析。SPI电离引发二溴甲烷增强化学电离对于还原性硫化物具有独特的选择性，直接检测灵敏度达到ppt级。项目中研制的新型仪器进行了有效的集成、示范应用，冷阱富集车载式质谱在北京四环、五环进行了环境中C2-C12的 VOCs污染物的车载式检测；在线质谱还实现了垃圾焚烧烟气中氯苯、氯酚前驱物的检测；下水道硫化物的检测以及六氟化硫绝缘全封闭组合电器中分解产物SO2、SO2F2、SOF2定量检测。项目共发表SCI文章10篇，其中Analytical Chemistry 5篇，Analyst 1篇，Talanta1篇，Chinese Chemical Letter 1篇，Chinese Journal of Analytical Chemistry 1篇，共申请专利9项，已授权3项。完成项目预期4篇文章、3-5项专利的指标。