RETENTION IN FIELD-FLOW FRACTIONATION WITH A MODERATE NONUNIFORMITY IN THE FIELD FORCE

In some held-how fractionation (FFF) techniques, the basic analyte-hel d interaction parameter, lambda, is not constant but varies within the channel cross section as a result of the nonuniformity of the force e xerted by the held on the analyte. This is the case, for instance, in thermal FFF, because of the temperature dependence of the relevant phy sicochemical transport parameters, To account for this effect, a new F FF retention model is developed, allowing a linear variation of lambda from the accumulation to the depletion wall, which is assumed to desc ribe correctly moderate nonuniformity in lambda in the vicinity of the accumulation wall, A methodology for sample characterization on the b asis of this model is proposed, It associates lambda(app), the apparen t lambda value derived from the retention ratio by means of the classi cal retention model, with a specific distance from the accumulation wa ll. An empirical relationship between that distance and lambda(app) is derived, In the high retention limit, it is found that this specific distance is not equal, as sometimes intuitively believed, to the mean distance of the molecule or particle cloud to the accumulation wall bu t is approximately equal to twice this mean distance. The validity of the proposed approach is checked.