Continuous Donnan Dialysis Sampler for Flame Atomic Absorption Spectrometry

Donnan dialysis occurs when an ion-exchange membrane separates aqueous solutions of differing ionic composition. A typical dialysis cell for analytical applications is shown in Fig. 1. The ionic strength differential causes transport of analyte ions of the appropriate charge sign from the sample into the receiver electrolyte. If the receiver ionic strength exceeds that of the sample by at least a factor of 100, and if the dialysis is not allowed to approach Donnan equilibrium, the rate of analyte ion transport into the receiver is proportional to the concentration of that ion in the sample and independent of sample matrix factors.