Physical Foundation and Definitions

IMS is the technology for separation of ionic mixtures and identification or characterization of ions by some property of their transport through a medium under the influence of electromagnetic fields. 

The science and technology of IMS has been developing rapidly over the last decade and now branches into two subfields conventional and differential IMS. The fundamental distinction between them is in the physical quantity underlying the separation (the separation parameter). 

Conventional IMS includes methods based on absolute ion transport properties that could be measured using a time-independent electric field. 

Differential IMS comprises methods dependent on a change of some ion transport property as a function of electric field and thus requiring a time-dependent field that substantially varies during the measurement. 

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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