Hydrodynamic relaxation using stopless flow injection in split inlet sedimentation field-flow fractionation

Abstract

In this paper relaxation effects in both the normal and steric operating modes of sedimentation field-flow fractionation are examined by using three different injection procedures: stop flow, stopless flow, and a new stopless flow procedure employing an inlet splitter. In the usual operation of field-flow fractionation (FFF), a stop procedure is used in which the channel flow is halted for an adequate period of time after injection for sample relaxation (in which the sample particles approach equillibrium near one wall) before the resumption of channel flow. If the channel flow is not stopped (stopless flow procedure), the elution profile is shifted and distorted due to the downstream migration of the particles during the relaxation process. To avoid peak distortion while retaining the advantages of the stopless flow procedure, a physical splitter at the channel inlet divides the entering flow stream into two substreams; sample is injected into only one of these. In this way a rapid (although not complete) hydrodynamic relaxation is realized. This stopless split flow injection procedure is compared to ordinary stop and stopless flow procedures using both submicrometer (normal FFF) and supramicrometer (steric FFF) polystyrene latex particles. It is found that much of the distortion normally accompanying stopless flow injection is eliminated by this new procedure. However, further optimization is needed to match the high resolution of the stop flow method.

Particle Trajectories in Field-Flow Fractionation and SPLITT Fractionation Channels

“…Two principal methods of reducing the band spreading incurred by slow migration toward equilibrium have been shown to be effective: stopped- flow relaxation (12)(13)(14) and hydrodynamic relaxation (15)(16)(17)(18). In the first, the sample is carried onto the channel at the normal channel flow rate, or at a reduced rate to aid in placing the sample reproducibly close to the channel inlet.…”

“…This fraction of the flow is confined hydrodynamically within a thin lamina adjacent to the accumulation wall by introducing the remaining fraction adjacent to the opposite (depletion) wall. This may be accomplished using either a split (15,16) or frit (17,18) inlet system. The split inlet has a thin plane splitter that extends a short distance into the channel.…”

Effect of Inlet Frit Lengths on the Hydrodynamic Relaxation Efficiency in Frit Inlet Asymmetrical Flow Field‐Flow Fractionation

“…Therefore, a sample component driven toward the accumulation wall will find an equilibrium slightly away from the wall. [8,9] However, band broadening always occurs during hydrodynamic relaxation when a FI-AFlFFF system is used, since it adopts the stopless flow injection method. The main advantage of using a frit inlet relaxation is to bypass stopflow relaxation, [6] or focu-sing=relaxation procedures, [7] that are normally carried out by stopping migration flow for a certain period of time to establish equilibrium conditions of sample components.…”

Hydrodynamic relaxation and sample concentration in field-flow fractionation using permeable wall elements

“…It also increases run time. Consequently, means have been pursued recently for introducing samples into FFF channels without stop flow operation (4,5).…”

“…One of the concepts developed and implemented in this laboratory for avoiding stop flow operation makes use of hydrodynamic relaxation, a process in which sample material is driven close to its equilibrium position rapidly by the manipulation of flow rather than by sluggish field-driven 0003-2700/90/0362-2306$02.50/0 transport in the channel (5,6). In the above-mentioned studies, hydrodynamic relaxation was proposed and carried out by using a flow splitter at the inlet end of the FFF channel.…”