Anomalous conductivity zones in electrophoresis I. Basic theory for two‐ion systems

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Abstract
The progressive increase in circuit resistance observed at times in polyacrylamide gel electrophoresis is attributable in part to the formation of zones of altered salt concentration at the interfaces between gel and solution. Similar changes have been reported for electrophoresis through sucrose gradients. Such zones must develop wherever migrant ions suffer a change in transport number. The paper develops a basic theory for such concentration changes. It is shown that a moving boundary will tend to arise at any interface between two media, leaving behind it a zone of altered concentration. The effect will in general be most noticeable at low ionic strengths and with electrolytes whose ions differ considerably in size, a condition applying to many common buffers. Where both ions are relatively small, diffusion is likely to obscure the boundary movement, but this will not affect the integrated change in concentration. The effect could have various deleterious consequences in gel electrophoresis, particularly in preparative apparatus. There are also implications for techniques such as isoelectric focusing and for the analysis of membrane phenomena.