THE ONLINE CHEMICAL-ANALYSIS OF SINGLE PARTICLES USING AEROSOL BEAMS AND TIME-OF-FLIGHT MASS-SPECTROMETRY

This paper describes an on-line instrument, capable of measuring the s ize and chemical composition of single aerosol particles. Possible app lications include monitoring aerosol reactors and studying atmospheric chemistry. The main conclusion is that a working prototype has been b uilt and tested. It uses a three stage vacuum system to generate an ae rosol beam with a low divergence angle and a high transmittance. The p ressure is reduced sufficiently to allow the application of a time-of- flight mass analyzer. The aerosol beam is probed in the analysis secti on by the focused beam of a low-power helium-neon laser. Every particl e crossing the laser beam scatters light, which is detected by two pho tomultiplier tubes, mounted at angles of 45 and 90 degrees. The signal is stored when both detectors produce a pulse simultaneously, and thi s event triggers the chemical analysis cycle. A pulsed Nd:YAG laser va porizes the particle and generates ions, which are next analyzed by a time-of-flight mass spectrometer. In this way combined information on the size and the composition of the particle is obtained.