Isoelectric focusing using non-amphoteric buffers in free solution: III. Separation of amino acids

Separation of proteins or amino acids by isoelectric focusing in multicompartment devices has been proposed for large-scale purifications of biological mixtures. In the perspective of industrial applications, the present authors built a multicompartment apparatus and studied the pH profiles stabilized by simple non-amphoteric buffers (acetic acid and sodium acetate). Mixtures of two amino acids were separated to test this device. A theoretical model comprising one dimensionless separation parameter is proposed to characterize these separations. This model allows one to calculate the purity of the recovered amino acids, the yield of a separation at steady-state or the time necessary to obtain a given concentration of an amino acid in one of the compartments of the isoelectric focusing cell. The separation parameter contains the physical parameters which intervene in the electric migration and in the diffusion. Values of this separation parameter have been experimentally determined for three amino acids under various experimental conditions. The results confirm the usefulness of this model in designing a multicompartment isoelectric focusing apparatus.