A Pinched Inlet System for Reduced Relaxation Effects and Stopless Flow Injection in Field-Flow Fractionation

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Abstract
The concept of a pinched inlet system for field-flow fractionation (FFF), in which the channel thickness at the inlet end is reduced to hasten relaxation, is introduced and its advantages in simplifying FFF operation and increasing analysis speed are noted. Three forms of FFF operation are described for taking advantage of the split inlet: stopless flow injection, slow flow injection, and stopflow injection. Stopless flow operation is the simplest because flow is neither stopped nor changed to accommodate relaxation. However, stopless flow operation causes band broadening. It is found that the time-based variance of band broadening for many FFF systems is proportional to the fourth power of channel thickness w. Therefore, by reducing w at the inlet end where relaxation occurs, this band broadening can be controlled. The implementation of this concept is discussed for different forms of FFF.