Initial development of single particle laser mass spectrometer

摘要

Based on the laser desorption/ionization, an experimental prototype of laser single particle time-of-flight mass spectrometer (TOFMS) was designed and constructed in our laboratory. Particles are inhaled directly from ambient air into a sampling inlet consisting of a short capillary nozzle and a two-stage differential pumping system. The particles are accelerated to different velocities depending on their aerodynamic diameter through free expansion of the air. The velocity of each particle is measured through two cross-positioned diode laser beam. A UV laser is fired at the exact time when the particle arrives at its focal zone to desorb/ionize the particle. The ions each firing generated are analyzed by a linear TOFMS and recorded automatically on a personal computer. The initial testing experiments including size calibration and practical measurements showed that the instrument is capable of analyzing the aerodynamic diameter and chemical constitutes of individual particle in real time. The information at single particle level allows each particle to be traced to its original source and provides immediate sense of atmospheric phenomena.