Chemically facilitated Donnan dialysis (CFDD) of heavy metal ions in combination with continuous reagent flow has been studied. A simplified model to describe this process has been established. The model relates the diffusion behavior of metal ions through a Nafion cation-exchange membrane with the stability constant of complexation, the ionic strength of the receiving and sample solutions, the flow rate of the receiving solution, and the area-to-volume ratio of the membrane dialysis cell. A novel fiber optic heavy metal sensor has been fabricated by directly interfacing the dialysis device with a fiber optic colorimetric detection mechanism