Cyclical-field field-flow fractionation: a new method based on transport rates

A new form of field-flow fractionation (FFF) is described in which the field strength is cycled up and down many times during a run. It is shown that this method, termed cyclical FFF (CFFF), leads to migration rates dependent on transport coefficients. After development of the general theory, results are obtained for coherent (no diffusion) square-wave operation. For the latter, migration rates are shown to depend on the generalized mobility of the particles and upon system parameters such as cycle time and field strength. Other variants of CFFF are noted and several advantages are indicated. A gravitational CFFF system operating according to sedimentation coefficients is described and certain programming options are discussed.

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