Single-particle aerosol mass spectrometer

The aerosol mass spectrometer described above is capable of analyzing particles of nonbiological origin. When used for analysis of CWAs, the BAMS instrument is named single-particle aerosol mass spectrometer (SPAMS). Using this instrument design, Martin and coworkers reported the successful detection of hquid nerve agent simulants from individual aerosol particles [55]. 

Aerosol beams are directed streams of small particles in a low pressure gas. They are formed when an aerosol expand.s from a high-pressure reservoir through a no/xle into a low-pressure chamber. Aerosol beams were discussed early in this chapter in connection with studies of particle rebound from surfaces. Such beams are also used to introduce particles into mass. spectrometers for single-particle chemical analysis (Chapter 6). The characteristics of the aerosol beam depend on particle size, nozzle configuration (converging or capillary), and skimmer arrangements. 

Trimborn et al. (2000) have developed a mobile system for the on-line analysis of single airborne particles and for the characterisation of particle populations in aerosols, using a transportable laser mass spectrometer. A schematic diagram of their setup is shown in Figure 3.12. 

More ambitious attempts at measuring the heterogeneity of the atmospheric aerosol have been undertaken as well. Single-particle analysis by mass spectrometry was demonstrated by Sinha and co-workers (31, 32). In this technique, an aerosol sample is introduced into a vacuum chamber in the form of a particle beam. The particles are injected into a Knudsen cell oven, where they undergo many collisions with the cell wall and are ultimately vaporized and ionized. The ions are then mass-analyzed with a quad-rupole or sector mass spectrometer. So that individual particles can be analyzed, the flux of particles into the Knudsen cell is limited so that coincidence errors are minimized. Ion pulses from individual particles allow the determination of the amount of the species being analyzed in the particular particle. The sensitivity of the technique is limited. For sodium, the detection... 

Peters SJ, Ewing GE (1997b) Water on salt An infrared study of adsorbed H2O on NaCl(lOO) under ambient conditions. JPhys ChemB 101 10880-10886 Peters A, Wichmarm HE, Tuch T, Heiruich J, Heyder J (1997) Respiratory effects are associated with the number of ultrafine particles. Am J Respir Crit Care Med 155 1376-1383 Phares DJ, Rhoades KP, Wexler AS (2001a) Performance of a single-ultrafine-particle mass spectrometer. Aerosol Sci Tech (accepted)... 

A laser ablation TOF mass spectrometer has been developed to iderrtily individual airborne micrometer-sized particles, comprising a single cell or a small mrmber of clumped cells (Tobias et al. 2005). This approach is reagerrt-less, and it relies on laser ablation and detection of lower mass (less than m/z 200) positive and negative ions. MS signatrrres for aerosolized Mycobacterium tuberculosis particles are distinct fromM smegmatis. Bacillus atrophaeus, and B. cereus particles. This technique is tested as a stand-alone airborne M. tuberculosis detector in bioaerosols from an infected patient at airborne concentrations of 1 particle/liter. 

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