Differential mobility

G.A. Eiceman, E.V. Krylov, N.S. Krylova, E.G. Nazarov and R.A. Miller, Separation of ions from explosives in differential mobility spectrometry by vapor-modified drift gas, Analytical Chemistry 76(17) (2004) 4937-4944. 

The device resembles a cylindrical differential mobility analyzer (DMA) in that a sample flow is introduced around the periphery of the annulus between two concentric cylinders, and charged particles migrate inward towards the inner cylinder in the presence of a radial electric field. Instead of being transmitted to an outlet flow, the sample is collected onto a Nichrome filament located on the inner cylinder. The primary benefit of this mode of size-resolved sampling, as opposed to aerodynamic separation into a vacuum, is that chemical ionization of the vapor molecules is feasible. Because there is no outlet aerosol flow, the collection efficiency is determined by desorption of the particles from the filament, chemical ionization of the vapor, separation in a mobility drift cell, and continuous measurement of the current produced when the ions impinge on a Faraday plate. 

FIGURE 11.65 (a) Electrical aerosol analyzer (adapted from Whitby and Clark, 1966). (b) Schematic diagram of differential mobility analyzer (adapted from Yeh, f993). 

Rosell-Llompart, J., I. G. Loscertales, D. Bingham, and J. F. de la Mora, Sizing Nanoparticles and Ions with a Short Differential Mobility Analyzer, J. Aerosol Sci, 27, 695-719 (1996). 

Magnesium nitride (Mg3N2) particles on a submicrometer scale were synthesized by evaporating magnesium metal in a pressure of 1 kPa of mixed NH3 + N2 gas flow kept at 800°C by a cylindrical furnace (41). Ge and In UFPs, which were size selected in advance with a differential mobility analyzer, were reacted with NH3 gas in a tube furnace at 1000°C to form size-selected GaN and InN UFPs (42). 

Figure 5. Transients observed in the concentrations of ultrafine particles in smog chamber studies of the photooxidation of dimethyl disulfide. Particles were measured with the electrical mobility spectrometer operating at fixed analyzer column voltages for the 11- and 20-nm sizes and with the differential mobility analyzer similarly operated for the 50-nm particles. (Reproduced from reference 49. Copyright 1991 American Chemical Society.)...

Size-resolved chemical information is much more difficult to obtain. The many applications of the differential mobility analyzer in measuring properties of size-classified particles are important tools for the characterization of aerosol systems, but the approaches demonstrated to date yield limited data. Vapor pressures, surface tension, and optical absorption have been measured on mobility-classified aerosols. Direct measurements of the distribution of chemical composition with particle size are needed. Elemental... 

The most often measured property of the LRT wildfire smokes is the mass concentration of aerosol particles in fine (PM2.5) or submicron (PMi) or in fine and coarse size fraction together (PM10). The mass concentration is usually determined either with a tapered element oscillating microbalance (e.g., [19]), or with the instruments based on p-attenuation (e.g., [13]). In addition to mass concentration, real-time instruments can measure other physical properties of particles, e.g., number concentration of particles in different size fractions using a differential mobility particle sizer [13] or the optical characteristics of smoke by a nephelometer [32]. Ground-based instruments also include remote sensing instruments such as sun photometers [32],... 

Note DMS differential mobility spectrometer, SMPS scanning mobility particle sizer, CPC condensation particle counter, TDMPS twin differential mobility particle sizer, DMPS differential mobility particle sizer, OPC optical particle counter, APS aerodynamic particle sizer, MAS mass aerosol spectrometer, LAS-X optical laser aerosol spectrometer, ELPI electrical low pressure impactor... 

Explosives Detection Using Differential Mobility Spectrometry... 

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