Transport properties of amino acid ions at isoelectric point in electrodialysis

• The concentrations of different ionic forms of amino acids were calculated.
• Acidic glutamic acid preferred to be negatively charged and migrate towards the anode.
• Basic lysine was inclined to be positively charged and migrate towards the cathode.
• The electrodialysis performance of lysine was better than that of glutamic acid.

The protonation and deprotonation reactions in systems containing amino acids play an important role and lead to some principal peculiarities of their transport in solution and membrane. A better understanding of the behavior of bipolar amino acid ions in electrodialysis would help a lot to facilitate or restrain the transfer of amino acids depending on the applications. In this work, the dissociation and migration of glutamic acid (acidic) and lysine (basic) in electrodialysis was ascertained using the special seven-compartment assemblies. It showed that acidic glutamic acid was inclined to be negatively charged and migrate towards the anode, while basic lysine preferred to be positively charged and migrate towards the cathode. Besides, the process performances of the same amino acids were also investigated during the conventional electrodialysis with the five-compartment assemblies. The pH and adsorption characteristics of membranes indicated that the above conclusion was valid for the conventional electrodialysis as well. Moreover, process parameters, i.e. overall current efficiency and energy consumption, were also assessed and compared for the electrodialysis of glutamic acid and lysine solutions.