Displacement chromatography on synthetic ion-exchange resins. 5. Separation of the basic amino-acids

Abstract

The use of sulfonated phenol-formaldehyde cation-exchange resins in the prepn. of displacement chromatograms leads to difficulties in the separation of basic amino acids. These difficulties are due to the phenolic hydroxyl groups of the resin, and an attempt has been made to avoid them by use of a sulfonated cross-linked polystyrene resin containing no phenolic hydroxyl groups.. Three samples of polystyrene resin prepd. in the laboratory and one commercial prepn. were investigated. Variations in the degree of cross-linking produced by variations in the amount of divinylbenzene used in the prepn. of the resin gave rise to important differences in the behavior of the sulfonated product towards organic bases. Two resin samples with a low degree of cross-linking gave sharp boundaries in displacement chromatograms using basic amino acids but suffered from the defect of excessive shrinkage with changes in the ionic strength of the solution phase. The most highly cross-linked laboratory sample and the commercial sample did not shrink excessively, but the boundaries observed in displacement chromatograms carried out under comparable conditions were very diffuse. To minimize the disturbances of the column associated with excessive shrinkage, 2 expedients were adopted: (a) the operation cycle was adjusted to avoid large changes in the ionic strength of the solution phase; (b) the continuity of the column packing was broken near the base of the column. Employing these expedients, mixtures of leucine, histidine, lysine and arginine were separated successfully.