车载生物气溶胶质谱仪用小型化双极质量分析器的设计

Design of Bipolar Mass Analyzer in Miniaturized Single Particle Aerosol Mass Spectrometry

  • 摘要: 生物气溶胶是大气中一类特殊的气溶胶,实时检测与识别生物气溶胶是实现生物预警预报的前提。小型车载生物气溶胶质谱仪对双极飞行时间(TOF)质量分析器的设计提出了要求。本研究基于指数脉冲延时引出技术开展小型TOF设计,结合SIMION 2020软件,模拟了速度分散为峰值800 m/s的高斯分布,空间分散0.3 mm情况下的粒子飞行轨迹。采用粒子群优化算法(PSO)自动优化TOF多组电极电压以及延迟时间。在130 ns延迟时间下,即使是极限的空间分散和能量分散也能实现全质量范围内的分辨率超过500,不同颗粒之间的质量偏差可控制在0.4 u以内。对比模拟分析了方波脉冲延时引出和指数脉冲延时引出对单个颗粒形成离子的分辨率影响,结果表明,指数脉冲延时引出在全质量范围内的分辨率显著优于方波脉冲。实验模拟了在颗粒处于光斑中心以及光斑偏左和偏右0.15 mm的极限情况下,颗粒电离位置对质谱分辨率的影响,结果表明,分辨率存在差异,但仍优于500。通过实际检测黑炭颗粒,小型TOF在全质量范围内可获得500以上的分辨率,能够满足车载生物气溶胶质谱仪的分辨率要求。虽然小型TOF的飞行长度为SPAMS 0525的67%,但分辨率可达SPAMS 0525的1.2~1.7倍,小型化生物气溶胶质谱的TOF体积仍有进一步减小的空间。

     

    Abstract: Biological aerosols are a special type of aerosols in the atmosphere, which have carcinogenic and teratogenic properties. Real-time detection and identification of biological aerosols is the prerequisite for biological warning and forecasting. The design of bipolar time-of-flight (TOF) mass analyzer is required to realize miniaturized vehicle bioaerosol mass spectrometer, with the mass range above 300 and mass spectrometry resolution at least 500. In this study, the exponential pulse delay elicitation technique was applied to the design of miniaturized TOF. Combined with SIMION 2020 software, the particle flight trajectory under the condition that the velocity dispersion was a Gaussian distribution with a peak value of 800 m/s and a spatial dispersion of 0.3 mm were simulated. The particle swarm optimization algorithm (PSO) was used to automatically optimize the voltage and delay time of the TOF. Under the optimized delay time of 130 ns, the resolution of more than 500 could be achieved in the full mass range even if the spatial dispersion and energy dispersion were in extreme cases, and mass deviation between different particles could be controlled within 0.4 u. The impact of normal square wave pulse delay extraction and exponential pulse delay extraction on the resolution of ions formed by a single particle was compared and analyzed. The results showed that exponential pulse delay extraction improves the resolution in the full mass range significantly better than square wave pulse. The effect of particle ionization position on mass spectrometry resolution was simulated when the particle was in the center of the spot and at the limit of 0.15 mm to left and right of the spot. The result showed that the resolution was different, but still better than 500. The detection of black carbon particles showed that the miniaturized TOF could obtain a resolution of more than 500 in the full mass range, which met the resolution requirements of the vehicle bioaerosol mass spectrometer. Although the flight length of the small TOF is 67% of that of SPAMS 0525, the resolution could reach more than 1.2-1.7 times due to the use of exponential pulse delay extraction technology. This study provides a design for a small time-of-flight mass analyzer, and indicates that there is still room for further reduction the size of time-of-flight mass analyzer for the miniaturized bioaerosol mass spectrometry. This study lays a research foundation for further reduction the volume of the subsequent bioaerosol mass spectrometer.

     

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