We report irreproducibility analysis of miniaturized, batch, continuous stirred tank Donnan dialyzers (CSDD) designed for a membrane-separation module of chemical analysis systems. Theoretical analysis indicates that a high exchange capacity of ion-exchange membrane > 1 mol L-1) causes a significant irreproducibility of the CSDDs when the dialysate/sample volume is relatively small ( < 10 mL) and the ionic strength is low ( < 0.01 M). Numerical simulation based on Nernst-Planck flux equation and Donnan-equilibrium equation shows a significant deviation from the ideal Donnan-dialyzer response, and this irreproducibility is verified with experiments. In order to address the irreproducibility issue, we introduce a novel, microfluidic, parallel-plate Donnan-dialytic membrane-separation module (PDMM) with recirculation tube. The recirculation tube works as a dialysate/sample container as well as an effective mixer. The rationally designed PDMM has advantages over the CSDDs in that (1) the dialysis throughput is improved (6 folds), and (2) the dialysis irreproducibility is reduced (4 folds). Dialysis efficiency of our PDMM is also high (similar to 91%), compared with that of flow-through parallel-plate dialyzers (usually similar to 1%). (C) 2014 Elsevier B.V. All rights reserved.