Small-Size and Low-Gas-Flow Designs

Three drift tube designs had been identified for small alMS instruments these are termed as follows  

A fourth design, a so-ealled second-order design, was introduced for which ion flow into the analyzer gap is narrow compared to the distance between plates of the drift tube. Two approaches to controlling effective widths of the inlet apertures have been (a) physical structures in the drift tube to introduce a thin band of ions into the main channel of mobility measurement by Zimmermann et al. ° and (b) electric fields to remove ions from all parts but a selected width from the eross section by Anttalainen.  

Zimmerman modeled and demonstrated an alMS design with low-cost fabrication by stacking together four inexpensive components. The ion swarm was narrow in width by fluid dynamics and by geometric constraints (i.e., a thin inlet aperture). The aperture for sample flow was about 10% that of the main mobility channel, and modeling showed some affects of unevenness in streams with joining two flows. Still, 

FIGURE 6.7 One alMS drift tube is commercially packaged as the Chem Pro lOOi. 

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