Preparative Isolation of Amino Acids by Carrier Displacement Chromatography on Ion Exchange Resins* by Donald

Chromatographic separations of amino acids on ion exchange resins may be performed on a preparative scale either by elution (24) or by displacement (5-12). Some of the exceptional resolving power demonstrated in analytical separations by elution techniques (13, 14) disappears when larger columns with relatively higher loads are used (2). Displacement chromatography allows large quantities of solute to be chromatographed on modest sized columns (12), but inherent in this technique is the disadvantage that solutes are mixed at zone boundaries. Furthermore, compounds of very similar structure are apt to emerge with large overlapping zones or are mixed throughout. These mixed fractions must be discarded or rechromatographed, thereby reducing the yield or increasing the labor. Quantitative recovery of pure material is theoretically impossible. With minor exceptions, bases and acids emerge from cation or anion exchange resin columns in an order inversely related to their strength (15). That this order is maintained, whether or not the substance is amphoteric, is evident from the data of Partridge (8), Partridge and Brimley (12), and Shewan et al. (16, 17). Glucosamine, ammonia, and trimethylamine oxide assume predictable positions in the displacement order. Because the two latter compounds, both easily removable free bases, eliminate the overlapping zone between adjacent ampholytes, it seemed likely that other bases might be found which would completely separate other pairs of amino acids in cationic displacement experiments and that acids would probably act in the same capacity with anion exchange resins. These separating acids and bases are called “carriers,” the term adopted by Tiselius and Hagdahl (18) to describe a series of alcohols which bring about separation of several amino acids and peptides on charcoal-Super-Cel displacement columns. Although non-ionic carrier displacement has had several applications (19-24) and the possible use of the principle in ion exchange chromatography has been recognized (12, 25), no previous