Other Drift Tube Designs

In this section, discussion is given to designs of drift tubes based on unusual or unconventional technology, material sciences, or designs and not mentioned in previous sections. These innovative designs are associated with historic drift tube methods since these are the most extensively developed in the past 40 years. 

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Other drift tube designs are possible. For example. Figures 3.10 and 3.11 show one such arrangement originating from the laboratory of one of the authors. Here the drift tube is constructed from a single piece of static dissipative Teflon and the metal electrodes are located on the outside of the tube. This design is adapted from a drift tube developed for... 

The other type of design relies on linear piezoelectric translational stages, which either move the sample or the scanner tube, while the other remains fixed. These designs do not suffer from the drawback mentioned above and can reproducibly position the scanner tube and thus the tip in x-y-direction. However, concerning stability/drift upon cooling, the beetle design is superior, because it is a very well balanced system. 

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... 

An attractive feature of this chopper-based method was the exclusion of ESI spray from the drift tube except for the brief period of ion injection. Aerosols were blocked from entering the drift tube most of the time, protecting the drift tube from the large burden of mass flux this made this design inherently clean, unlike other ESI IMS designs, for which a large demand exists for a drift tube to accept an aerosol-rich flow, which must be desolvated and swept from the drift tube. Injection pulse widths... 

Conventional IMS is often called drift tube IMS (DTIMS) because the constant electric field is commonly established in tubes where ions drift along the axis. However, implementations of conventional IMS vary and other designs have emerged in both research and commercial systems. Some, such as traveling wave IMS (TWIMS), acmally employ a time-dependent field, but that is for instrumental reasons and does not affect the separation parameters. 

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