离子富集式无窗VUV光电离源及其在便携式TOFMS现场检测VOCs中的应用

Volatile organic compounds (VOCs) is one of the critical pollutants in the air and the water. Due to the shortage of in-situ and rapid detection equipment for environmental pollutants in China, it is very hard for the government of China to monitor the VOCs pollutants in the air,the revisers, lakes and underground, or toxic compounds in environmental emergency accident. Vacuum ultraviolet photon soft ionization portable mass spectrometry is a kind of analytical instrument for continuous and real-time analysis of VOCs pollutants, and can monitor the changes over time for the pollutants.But the requirement of portability for mass spectrometry sacrifices its sensitivity, it is difficult to online detect trace analytes with portable mass spectrometry. This project aims to design a new ion-enrichment windowless VUV photon ionization source for online high sensitivity analysis of trace VOCs with time-of-flight mass spectrometry (TOFMS). And this project mainly focus two ways on improving the sensitivity: improving the photon flux and the utilization rate of ion from ion source to mass analyzer. The radio frequency voltage drived windowless high flux VUV lamp is used to improve the amounts of the ions for analytes. Segmented quadruple instead of traditional four-round quadrupoles is used to focus the radical ions. A tandem quasi-trapping ion trap locate after the segmented quatrupole, and it slow down ion movement rate, enrich the ion concentration. A Bradbury-Nielson Gate (BNG) locates in the end of the quasi-trapping ion trap. When the mass-to-charge separation performed by the TOFMS analyzer, the BNG was closed and the ions were concentrated inside of the tandem quasi ion trap, and high efficient use of ions was achieved by this method. In this design, the windowless VUV lamp and ion enrichment were integrated into the ionization source, and this kind of design saves space and improves the sensitivity, and it will has a wide range of applications in real time analysis of VOCS/SVOCs with on-line TOFMS.

VOCs是空气中、水体中重要的污染物，国内现场快速检测仪器的短缺使得环境污染物、环境应急事故中有毒有害化合物难以实现有效监控。以真空紫外光软电离的便携式质谱可实现水中VOCs实时检测，但其便携性的需求牺牲了灵敏度，痕量有毒有机物难以检测。本项目围绕痕量VOCs现场质谱监测灵敏度需求，研制离子富集式无窗VUV光电离源来提高灵敏度。从离子产生数量和离子利用率两个方面着手提高仪器灵敏度；利用射频电压放电在低压下设计无窗高光通量VUV灯；在电离源内采用片段四极透镜径向聚焦源内分散的离子；离子传输区内以串级准离子阱延缓离子轴向运动速率，提高传输通道内离子数浓度；TOFMS质量分析期间关闭离子门，以串级准离子阱与脉冲DC电场富集离子；打开离子门，将被富集的离子引入TOFMS实现离子高效利用。将该器件与垂直加速式便携TOFMS联用，开展VOCs等有毒有害化合物现场快速检测。

真空紫外（VUV）灯单光子电离是软电离，仅得到样品分子离子峰，但商品化VUV灯光通量小在质谱中使用灵敏度低。本项目基于介质阻挡放电、射频线圈激发高纯 Ar 放电设计11.6/11.8 e V 的高强度光束无窗VUV灯，有效提高光通量。电离源内设计了片段四极透镜径向富集空间分散的离子，实现电离、离子聚焦一体化离子源，灵敏度提高60倍以上。设计的VUV灯试剂辅助化学电离源微型离子阱质谱软电离毒品，有效去除汽车尾气干扰；设计的光闪热毒品热解析系统使得芬太尼类毒品灵敏度提高了10倍；光热解析结合脉冲同步进样，便携式离子阱系统灵敏度达到10 pg，沸点差距300℃的10种毒品混合物在3s内一次分析同时检出，仪器于2018年通过了“公安部刑事技术产品质量监督检验中心”认证，在云南边境缉毒现场示范应用。研制的便携式飞行时间质谱（TOFMS）应用于六氟化硫绝缘全封闭组合电器中分解产物SO2、SO2F2、SOF2¬现场不停电定量检测，在广西电网110 kV变电站进行连续三个月示范应用。针对痕量挥发性气体检测发展了冷阱高效富集技术，富集效率高达200倍；针对水中VOCs直接分析发展了电离源内螺旋膜进样低气压光电离TOFMS，实现下水道废水中痕量VOCs的在线测量。研制的动态吹扫-释放试剂分子辅助大气压光电离源质谱用于海水中三甲胺检测，2 min分析时间仅消耗2 mL海水样品的条件下定量限低至59 ng L-1。光电离在线质谱直接分析呼出气中C3-C6正构烷烃，检出限低至0.07 ppbv。光电离TOFMS以 0.5 s时间分辨实现甲醇制烯烃初始反应阶段乙烯、丙烯生成顺序的在线分析，对乙烯、丙烯的检出限分别低至 16.98 和9.64 ppbv/0.5 s，为第一个 C-C键形成机理研究提供有力的数据支撑。项目中研制的VUV软电离在线质谱可广泛应用于环境污染物、爆炸物、毒品及化学反应中间产物的在线快速鉴定。项目在Analytical Chemistry 发表3 篇，Trend in Analytical Chemistry 1篇，Analytica Chimica Acta 2篇，Analyst 1 篇，Talanta 1 篇，Chinese Chemical Letter 1 篇，Analytical Methods 1篇，分析化学3 篇。申请发明专利 15 项，其中授权 4 项。