Background and principles of DMS

In the early to mid 1980s, the characterization of ions with field dependence of mobility was treated theoretically [36] and was based on the following concept if ions had the same mobility but differing dependence of mobility with E/N, then the characteristic differences in mobility could be a basis for ion separation. Thus, a complete expression of mobility is shown in Eq. 3, where the mobility coefficient contains a non-linear 

alpha is associated with a difference in mobility of the ion may be positive or negative in sign, which discloses the direction of change in the coefficient of mobility (and compensation voltage) with E at constant N. In practice, ions are characterized by 

Without intervention, all ions apart from those with no dependence of mobility on field will strike a wall, be neutralized, and be swept as a neutral from the analyzer. However, a DC voltage (the compensation voltage) can be added to the bottom electrode and superimposed on the megahertz waveform (Fig. 6). As this potential is applied, ion 

The principle for alpha dependence is rooted in ion behavior through collisions and associations with molecules of the supporting atmosphere, and a comprehensive treatment has been given. 

In summary, ions that exhibit a positive dependence of K on E/N can be understood to undergo clustering and declustering events as shown in Fig. 8. During a low-field portion of the waveform, ions are not electrically heated or are slightly over thermal energies, and associations with water and supporting atmosphere can occur with lifetimes proportional to the heats of association. These associations result in increases in flD and decreases 

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