Aerodynamic time-of-flight

This technique has been extended by inclusion of a pulsed ionization laser to vaporize the particles after their size has been determined by aerodynamic time of flight. This causes the particle to vaporize and the resulting fragments are partly ionized. Positive ions are accelerated into the flight tube of a mass spectrometer where their chemical composition is determined [141]... 

Another time-of-flight instmment, the Aerodynamic particle sizer (APS), is manufactured by TSI Incorporated (St. Paul, Minnesota). This system operates at subsonic flow conditions and cannot tolerate as high a flux of particles as the AeroSizer. As of 1996, the development of time-of-flight instmments is ongoing. 

RW Niven. Aerodynamic particle size testing using a time-of-flight aerosol beam spectrometer. Pharm Technol 17 72-78, 1993. 

TSI Model 3800 Time-of-Flight Mass Spectrometerwas developed in cooperation with the University of California as the first single airborne particle mass spectrometer to be offered commercially. It uses an aerodynamic sizing technique to size individual particles in real time. It then desorbs and ionizes the particle for chemical analysis in a bi-polar, time-of-flight mass spectrometer. It operates in the 0.3 to 3 pm with an optional disperser to extend the range to 10 pm. The instrument can save positive and negative mass spectra at a rate up to 10 particles per second [142]. 

Figure 1 Compilation of data collected from Refs. 12 and 23 to 30 showing fine particle fraction (FPF), versus volume mean aerodynamic diameter c/a, for micronized and SCF-processed powders investigated. Values of c a obtained by using the AeroSizer time-of-flight technique when available (23,24,26,30) or recalculated from the mean volume (geometric) particle diameters cfy- obtained from laser diffraction and scanning electron microscope data (12,25,29) by applying the conversion algorithm developed by Shekunov et al. (24).

A particle-sampling mass spectrometer could provide a useful approach to measuring inhalation exposure to pollutants in a wide variety of environments. One example17 employs an aerodynamic lens that samples very fine particles and creates a beam that can be modulated to give a crude time-of-flight mass distribution. The particles impinge on a hot surface, causing vaporization of constituents that can be ionized (by electron impact or photoionization) and subjected to mass analysis by any of several kinds of mass analyzers. 

Mannitol (99%) was supplied by Pfanstiehl Lab (Waukegan, Illinois), myoinositol (99%) by Sigma. Carbon dioxide (99%) and nitrogen (99%) were supplied by Air Gas. Samples of micronized powders were analyzed by a scanning electron microscope (ISl, model SX-30). The mean aerodynamic particle size distribution was measured using the Model 3225 Aerosizer DSP, which uses a laser time of flight principle. 

Mitchell IP, Nagel MW. Time-of-flight aerodynamic particle size analyzers then-use and limitations for the evaluation of medical aerosols. J Aerosol Med 1999 12(4) 217-240. 

Figure 4.7 Schematic of the time-of-flight aerosol mass spectrometer (TOF-AMS). Aerosol is introduced into the instrument through an aerodynamic lens focusing the particles through a skimmer and an orifice onto the vaporizer. Particle vapor is ionized and the ions are guided into the TOF-MS, which generates mass spectra at 83.3 kHz repetition rate. For particle size measurement the particle beam is chopped with a mechanical chopper and the detection is synchronized with the chopper opening time [178], Aerosol Science Technology A New Time-of-Flight Aerosol Mass Spectrometer (TOF-AMS) - Instrument Description and First Field Deployment. 39 637-658. Copyright 2005. Reston, VA. Reprinted with permission...

R. W. Niven, Aerodynamic Particle Size Testing Using the Time of Flight Aerosol Beam Spectrometer , Pharm. TechnoL, 17 (1993) 72—78. 

Salt, K. Noble, C. A. Prather, K. A. Aerodynamic particle sizing versus light scattering intensity measurement as methods for real-time particle sizing coupled with time-of-flight mass spectrometry. Anal. Chem. 1996, 68, 230-234. 

To address these deficiencies and others with the Mk-III, development of an improved bomb—the Mk IV—began in 1947. When deployed in 1949, the Mk-IV Fat Man had improved aerodynamic properties that eliminated the wobble problem. Moreover, the new design permitted the nuclear explosive core to be inserted during flight, enhancing in-flight safety and adding considerably to the service life of each homb. The Mk IV remained in the U.S. nuclear weapon stockpile until 1953. By the time the last of the Fat Man series of bombs was removed from service in 1953, about 250 of them had been produced. 

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