Twin Drift Tube

One of the most impressive developments during the past year or so with traditional drift tubes is the introduction of an IMS analyzer with authentic twin drift tubes where the sample is ionized in a single reaction region and positive and negative ions are extracted and characterized in two separated drift tubes placed at appropriate polarity. In this design, the two drift tubes can be individually controlled in temperature although the ion source is common to both drift tubes. The analyzer... 

A new analyzer based on ion mobihty has been introduced in 2005 and combines DMS and IMS analyzers in tandem, hence ions are first separated in a DMS drift tube and then characterized by twin IMS drift tubes [62]. Because the DMS is comparatively slow (0.1—1 Hz) and the mobihty spectrometer operates at 30 Hz, mobility spectra can be obtained throughout a DMS sweep of compensation voltage, creating a three-dimensional plot as shown in Figure 12 for DNT and TNT (unpublished experimental results provided by C.R. White et al. at New Mexico State University, September 2005). As shown in the topographic plots of Figure 12, a benefit of ion characterization for K and AK is seen in the improved separation of peaks over DMS and IMS alone. The tandem DMS-IMS was described at the 2005 International Symposium on IMS and is under development requiring detailed evaluation as drift tube improvements are made. 

Ar. Proton transfer to Ar was observed in a flow-drift tube study [32]. The dependence of the absolute cross sections for the N2D + Ar->ArD +N2 reaction in the forward and reverse directions on the center-of-mass kinetic energy of the colliding particles (0 to 15 eV) was studied using a twin mass spectrometer apparatus [33]. 

Brown and Skrebowski [37] first suggested the use of x-rays for particle size analysis and this resulted in the ICl x-ray sedimentometer [38,39]. In this instrument, a system is used in which the difference in intensity of an x-ray beam that has passed through the suspension in one half of a twin sedimentation tank, and the intensity of a reference beam which has passed through an equal thickness of clear liquid in the other half, produces an inbalance in the current produced in a differential ionization chamber. This eliminates errors due to the instability of the total output of the source, but assumes a good stability in the beam direction. Since this is not the case, the instrument suffers from zero drift that affects the results. The 18 keV radiation is produced by a water-cooled x-ray tube and monitored by the ionization chamber. This chamber measures the difference in x-ray intensity in the form of an electric current that is amplified and displayed on a pen recorder. The intensity is taken as directly proportional to the powder concentration in the beam. The sedimentation curve is converted to a cumulative percentage frequency using this proportionality and Stokes equation. 

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