Flow injection analysis (FIA) is a continuous flow technique developed in the early 1970's. FIA is based on reproducible sample injection, accurate timing and controlled dispersion. This technique is very versatile due to the control of the variables and can easily be automated. This technique is very suitable for routine laboratory analysis. By introducing various sample modifying techniques in tandem with the FIA system, samples can easily be modified. Some modifying techniques are analyte pre-concentration, sample dilution and sample cleanup. Passive dialysis can be used very successfully for sample dilution and cleanup. Problems arise when samples with low analyte concentration have to be analysed. For this reason an electrodialyser unit, equipped with a passive membrane, was developed. The history, development and theory of membranes and membrane processes are discussed. A study of the movement of ions, in solution and across a passive membrane, under the influence of an applied d.c. electrical potential is given. Passive membranes were evaluated for use in the proposed system. The following factors influencing the efficiency of electrodialysis in the F1 system were studies. The flow rate of the donor and acceptor channels; the applied d.c. electrical potential; injection loop volumes; flow direction in the electrodialyser unit. An investigation was done into on-line analyte pre-concentration and regulated dilution probabilities of the electrodialysis system. Systems that were evaluated are the following: The determination of chloride in water effluents; the determination of copper and zinc in pharmaceuticals; the direct and indirect determination of phosphate in fertilizers. A comparative study between the advantages and disadvantages of the passive dialysis and electrodialysis system is given. / Thesis (PhD (Chemistry))--University of Pretoria, 2006. / Chemistry / unrestricted