基于复合软电离源飞行时间质谱的小型化大气非甲烷烃在线快速监测系统的设计与应用

针对大气非甲烷烃(NMHCs)的时空分布监测需求,并弥补现有监测技术时间分辨率低、体积和功耗较大的不足,本研究自主研发出一套高性能、小型化的大气非甲烷烃在线快速测量系统.该方法基于串联吸附剂在特定温度下对目标物质的富集与解吸,采用单光子/化学复合软电离源飞行时间质谱(SPI/CI-TOFMS)作为分离和检测手段,实现对C_2～C_(10)挥发性有机物的快速分离和检测.通过对标准样品的测量表明:在SPI/CI模式下,C_2～C_(10)物种工作曲线(0～10×10~(-9))拟合优度R~20.99,大部分物种方法检出限为1×10~(-12)～80×10~(-12),仪器检出限为1×10~(-12)～35×10~(-12),RSD(n≥10)小于10%.将仪器初步应用于北京大学站点进行定点观测,测量结果与商业化仪器TH-300B离线分析结果吻合.本系统样品分析时间5～12 min可调,整机重量低于40 kg,整机尺寸小于50 cm×50 cm×80 cm,功率低于500 W,可满足大气非甲烷烃的快速监测需求,为提供高分辨率大气NMHCs时空分布数据提供技术支持.

Design and application of a non-methane hydrocarbon fast online-monitoring system based on combined soft ionization time-of-flight mass spectrometry

To address the crucial needs for temporal and spacial distribution of non-methane hydrocarbons (NMHCs) with high resolution, and overcome some of the major deficiencies of GC based VOC detection methods, e.g., low temporal resolution, cumbersome, and high energy consumption, herein we report on the development and application of a high-performance NMHCs online measuring instrument. The novel instrument is based on the preconcentration of ambient C₂~C₁₀ NMHCs via adsorption and thermal desorption by multi-bed adsorbents, and separation and fast detection of single photon ionization/chemical ionization time-of-flight mass spectrometry (SPI/CI-TOF-MS). Method detection limits (MDL) in volume ratio for most C₂~C₁₀ NMHCs species in a standard sample range from 1×10^-12 to 80×10^-12, while instrument detection limits range from 1×10^-12 -35×10^-12, making the instrument well-suited for fast measurements of ambient NMHCs. R² of standard curves for all measured species are above 0.99, and the RSD of 10 repetitive trials is less than 10%. We applied the instrument at Peking University, the system showed a robust performance. These results agree well with offline measurements from a commercialized instrument, TH-300B, with a deviation below 50%. The time resolution of this system is adjustable, usually 5~12 min; the weight of the whole machine is less than 40 kg, which physical dimension is less than 50 cm×50 cm×80 cm and the power consumption less than 500 W. With its high temporal resolution, small dimension, and high sensitivity, this instrument is able to provide realtime observations of ambient NMHCs, supporting further investigation of VOCs chemistry via model validation and future control policy over these ozone precursors.