Increase of the particle hit rate in a laser single-particle mass spectrometer by pulse delayed extraction technology

Abstract

Abstract. 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.