Study of mass transfer in on-line analytical parallel-plate dialysers in series in flow injection systems

Mass transfer of an analyte in passive dialysis was studied for two single membrane on-line dialysers in a tandem mode in series as well as a double membrane on-line dialyser in a flow injection system. The establishment of a suitable concentration gradient between the different channels was an important factor in mass transfer efficiency. A fast linear increase in copper(II) concentration occurred for the first 200 min in the first recipient streams of both dialysis systems due to the relatively large concentration gradient during this period whereafter the increase tended to slow down. The second recipient streams of both systems showed a very slow gradual increase in copper(II) concentration for the first 20 min, whereafter the increase speeded up owing to the development of a suitable concentration gradient. Comparison of concentration differences between the first recipient as well as the second recipient streams of the two different dialysis-flow injection systems revealed a faster increase in dialysis rate and mass transfer efficiency initially for a certain period for the single membrane on-line dialysers in series than for the double membrane on-line dialyser. They subsequently became equal whereafter the situation was reversed. It became evident that passive dialysis in flow injection systems is suitable for controllable dilution on-line.