Reply to Comments on the separation efficiency of asymmetrical Flow Field-Flow fractionation in channels of constant channel and crossflow velocities leading to constant separation efficiency

The membrane or cross-flow velocity in asymmetric Flow Field-Flow fractionation is not constant in usual geometries. Previously theoretical models however were developed with the hypothesis of a constant membrane velocity. The argument about peak broadening in the comments of K.-G. Wahlund (J. Chromatogr. A 1218 (2011) 6848) is based on this kind of model. Such an assumption was not included in the recently proposed model used to determine the conditions of constant velocities. The model goes beyond this approximation and anyway can provide the two velocity fields in various geometries.