STUDY OF MASS-TRANSFER IN ONLINE ANALYTICAL PARALLEL-PLATE DIALYZERS IN SERIES IN FLOW-INJECTION SYSTEMS

Mass transfer of an analyte in passive dialysis was studied for two si ngle membrane on-line dialysers in a tandem mode in series as well as a double membrane on-line dialyser in a now injection system. The esta blishment of a suitable concentration gradient between the different c hannels was an important factor in mass transfer efficiency. A fast li near increase in copper(II) concentration occurred for the first 200 m in 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) concentrati on for the first 20 min, whereafter the increase speeded up owing to t he development of a suitable concentration gradient. Comparison of con centration differences between the first recipient as well as the seco nd recipient streams of the two different dialysis-flow injection syst ems revealed a faster increase in dialysis rate and mass transfer effi ciency initially for a certain period for the single membrane on-line dialysers in series than for the double membrane on-line dialyser. The y subsequently became equal whereafter the situation was reversed. It became evident that passive dialysis in flow injection systems is suit able for controllable dilution on-line.