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Increase of the particle hit rate in a laser single-particle mass spectrometer by pulse delayed extraction technology
摘要： A single-particle mass spectrometer (SPMS) can provide a wealth of valuable information on chemical and physical parameters of individual particles in real time. One of the main performance criteria of the instrument is efficiency of particle detection (hit rate). Most SPMS instruments use constant electrical field (DC) extraction, where stationary high voltage is applied to the extraction electrodes. As the aerosol particles initially carry a certain charge, those with a high amount to charge can be deflected by this electric field and lost, thus decreasing the hit rate. We realized that the delayed extraction technique can eliminate the stochastic dispersion of the particle beam caused by their deflection in the stationary electric field. As the result, the hit rate of the instrument can be significantly improved. Also, as the effect of the deflection in the electric field is mass dependent, it can cause distortion of the measured size distribution of the particles. Hence, the delayed extraction technique can bring the recorded distribution closer to the actual one. We found that the delayed extraction technique provides a mass resolution improvement as well as increases the hit rate. The gain in the hit rate depends on the type of particles. It can be 2 orders of magnitude for model particles and up to 2–4 times for ambient particles. In the present work we report experiments and results showing the effect of the delayed extraction on the beam divergence caused by particle charge, the hit rate improvement, and the effect of the delayed extraction on the measured particle size distribution.
关键词： hit rate,particle charge,aerosol particles,delayed extraction,single-particle mass spectrometer
更新于2025-09-23 15:19:57
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Quantifying and improving the optical performance of the Laser Ablation Aerosol Particle Time of Flight Mass Spectrometer (LAAPToF) instrument
摘要： Single particle mass spectrometer (SPMS) instruments have been used for in-situ chemical characterization of atmospheric aerosols, both in the field and laboratory, for over two decades. SPMSs typically combine precise optical particle sizing with laser desorption and ionization followed by time of flight mass spectrometry. Among the advantages of SPMSs over other aerosol chemistry measurement techniques are their single particle resolution and high sensitivity counting efficiency in the size range 500-2000 nm vacuum aerodynamic diameter. We also present mass spectral performance for characterizing atmospherically-relevant particles in a comparison to a current SPMS design, the Particle Analysis by Laser Mass Spectrometry. The AeroMegt Laser Ablation Aerosol Particle Time of Flight Mass Spectrometer (LAAPToF) is a commercially available member of this instrument class, aiming for a compact size and simplicity for the end user. This paper quantifies the performance of LAAPToF with an emphasis on optical counting efficiency. Recommendations for improving detection compared to the base LAAPToF hardware are described. Our results show that changes to the optical detection scheme can lead to over two orders of magnitude improvement in optical counting efficiency.
关键词： aerosol chemistry,LAAPToF,Single particle mass spectrometer,optical counting efficiency,time of flight mass spectrometry
更新于2025-09-19 17:13:59