Onset of sample concentration effects on retention in field‐flow fractionation

Abstract

In field-flow fractionation (FFF), when the sample amount is increased, a shift in retention occurs. Positive as well as negative deviations of the retention have been observed, depending on the type of sample and on the experimental conditions. Two concentration effects have been invoked to explain this retention shift: the viscosity effect (the velocity profile of the analyte suspension or solution is modified by the concentration dependence of the viscosity) and the mean distance effect (the mean distance of the analyte molecules or particles to the accumulation wall and the steady state cross-sectional concentration profile of the analyte are affected by concentration-dependent interactions between analyte molecules or particles). The general FFF retention equation has been solved in the case where the reciprocal of the viscosity and the FFF analyte-field interaction parameter, k, are linearly related to concentration. The two proportionality coefficients involved in these relationships are identified as the intrinsic viscosity and twice the second virial coefficient of the osmotic pressure, respectively. A general expression of the derivative of the analyte average relative velocity, R, with respect to the cross-sectional average analyte concentration, pcP, has been obtained as a function of these two coefficients, and of k o , the limit of k for infinite dilution. A survey of retention effects reported in FFF literature for various sample types and FFF methods is presented.

Recovery, overloading, and protein interactions in asymmetrical flow field-flow fractionation

“…Various studies have been conducted to investigate the factors that lead to sample loss and mass overloading. However, few have investigated a larger selection of proteins and membranes [ 15 , 21 ] or attempted to explain the overloading theoretically [ 23 , 26 – 28 ]. We conducted a systematic study comparing five proteins of different molecular weight (MW) and isoelectric point (pI) and different membranes, and we derived a theoretical equation that predicts the reduction in zone velocity because of the viscosity effect.…”

ICP-MS for the analysis at the nanoscale – a tutorial review

“…In addition sample overload is critical in FFF as demonstrated by Martin et al reporting a shift in retention time with increasing sample amount. 167 Depending on the sample composition they observed positive as well as negative deviations of retention. Under specific conditions high sample concentrations are not avoidablefor instance, in order to allow satisfactory detection of analytes with low response factors or in case of fraction collection via preparative FFF.…”

“…In case of analytes behaving like random coils, the viscosity effect dominates. 167 To avoid undesirable effects regarding sample overload, it has been recommended to compare retention time and recovery rates for sample masses that differ at least by a factor of five. If the obtained results show no increase or decrease of retention times with increasing injected mass, no significant effect of the sample load occurs within the mass range tested.…”

Adverse-Mode FFF: Multi-Force Ideal Retention Theory

“…Most complications negatively impact separation [48]. Such complications may include flow profile distortion by the external field [43,49,50], hydrodynamic interactions leading to wall-induced lag [51,52], finite-aspect ratio channels [53], slip [54] and concentration effects [55]. On the other hand, a minority of complications may be beneficial to separation.…”