Ion shutter

Another interest in drift tube improvements is the poor performance of certain components such as the ion shutter, the device used to inject ions into the drift region... 

A modification of the conventional flowing afterglow apparatus, in which a drift section is incorporated, is shown schematically in Fig. 6.46i-141 In the so-called flow-drift apparatus reactant ions are produced in the upstream section just as in the conventional afterglow system, but the downstream section, where reactions with neutrals occur, is a drift tube, in which a uniform electric drift field is applied. In the latter section ions can be accelerated from thermal kinetic energies to several electron volts. The two sections of the apparatus are separated by an electronic ion shutter, which makes it possible to admit narrow pulses of ions into the drift region at specified times. This permits measurements of ion-drift velocity and, in... 

Differential mobility spectrometers are attractive through the mechanical simplicity of an analyzer assembly without ion shutters, an aperture grid, or multiple components to establish a voltage gradient to move ions as found in conventional IMS drift... 

Ion shutters with parallel wires for ion injection, first published mobility spectrum with drift time axis 18... 

Indeed, Robert J. van de Graff not only described ion shutters known today as Bradbury-Nielson (BN) shutters but also was the first to publish a mobility spectrum recognizable today in a standard format of detector response versus drift time (Chapter 2, Figure 2.1). Regardless of implementation, wire grids are today the... 

FIGURE 5.1 Designs of ion shutters with Bradbury-Nielson on left and Tyndall-Powell on right with end view and side view (a). Two waveform plans (b) a waveform is applied to each grid. A voltage difference on adjacent wires creates an electric field, and ions are drawn to wires and collide. Resultant neutrals are swept with drift gas from the analyzer. In each plan, wires are brought to a common potential, which is referenced to the voltage divider of the drift tube. 

FIGU RE 5.2 Photographs of (a) lyndall-Powell ion shutter and (b) Bradbury-Neilson shutter. 

FIGURE 5.3 Grid for ion shutter. Two grids of this design have been employed on drift tubes built for 3QB in Israel. (Courtesy Z. Karpas.)... 

The width of the waveform pulse applied to wires in an ion shutter is the key parameter in establishing peak widths in a mobility spectrum since the minimum possible width of an ion swarm, before normal diffusion and other influences in the drift region, is set by the shutter pulse time. The minimum time of a pulse, even in a well-designed and well-built instrument, is fixed by the time for ions, under mobility control of the superimposed electric field of the drift tube, to pass from one side of a shutter grid set (reaction region) to the other side (drift region). Injection pulses of about 100 ps are... 

Static and dynamic models for ion shutters were developed as a joint effort of computational models and experimental measurements for which electric fields were... 

FIGURE 5.6 Plots of ion count for (a) reactant ions as a function of electric field within the ion shutter E, at ambient temperature for the following values rectangles, 175 V/cm circles,... 

V/cm triangles, 275 V/cm stars, 325 V/cm and diamonds, 375 V/cm and (b) when was normalized to corresponding drift fields E. (From Tadjimukhamedov et al., A study of the performance of an ion shutter for drift tubes in atmospheric pressure ion mobility spectrometry computer models and experimental findings. Rev. Sci. Inst. 2009. With permission.)... 

While useful in certain research studies, this type of control of ion shutters and drift tubes was impractical for more complex chemical measurements and analytical applications. Nonetheless, a nearly identical strategy was employed with the Franklin GNO model Beta VI, the inaugural commercial IMS instrument in 1970 (Figure 2.2a) ion shutters of the BN design were operated with rectangular waveforms instead of the sinusoidal waveforms of Tyndall. A dual-shutter approach was used largely due to relatively slow data acquisition capability of that era, and... 

Multiplex Control of Ion Shutters to Improve Duty Cycle of Ion Injection through Shutters... 

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