A Definition of Ion Mobility Spectrometry

The length of drift regions for modem in-field IMS analyzers is typically 4 to 20 cm. An ion swarm moving 6 cm with a drift time of 15 ms in an electric field of 200 V/cm has a drift velocity of 4 m/s. The normalization of drift velocity to E produces the mobility coefficient K, which is swarm velocity per unit field (cm /Vs)  

FIGURE 1.1 A proliferation of mobility methods occurred during the past decade, ranging over dimensions, pressnres, and arrangements of electric field (constant or time dependent). Pressure of measurements is given in the fill pattern of boxes for individual methods. 

Describing ion mobilities with values of is a common and useful practice yet subtly complex and can be somewhat confusing. Mobility formulas were derived from studies of ions in nonclustering atmospheres, often at low pressures of 1 to 10 torr. Reduced mobility values may accurately account for ion molecule processes for measurements in low pressures with nonclustering gases such as He however, normalization for pressure and temperature alone cannot account for changes observed in all 

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