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

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.

Keywords

• biological aerosols
• single particle aerosol mass spectrometry (spams)
• pulse delay extraction
• time of flight mass analyzer