Separation of neutral amino acids on columns packed with polystyrene-based strongly acidic cation exchange resins with low ion exchange capacity

A series of polystyrene-based strongly acidic cation exchange resins with different ion exchange capacities were synthesized via the reversed-sulfonation of a commercial polystyrene-based strongly acidic cation exchange resin (001 X 7) or sulfonation of styrene-divinylbenzene copolymer. The chromatographic separation of alanine and valine or valine and leucine on columns packed with these resins was carried out. The results showed that the chromatographic properties of the two kinds of the above-mentioned resins on the separation of alanine and valine were almost the same. The retention volume of alanine was less than that of valine on the same column with various ion exchange capacities, and the retention volume of valine was less than that of leucine on the column with the ion exchange capacity of 1.67 mmol/mL. The retention volume of alanine decreased when the ion exchange capacities decreased from 2.02 to 1.00 mmol/mL. The retention volume of valine slightly decreased when the ion exchange capacities decreased from 2.02 to 1.67 mmol/mL and remained almost unchanged when the ion exchange capacities decreased from 1.67 to 1.00 mmol/mL. These results indicated that the interaction between neutral amino acids and the polystyrene-based strongly acidic cation exchange resin includes ionic and hydrophobic interactions. And there may be synergy between the two interactions. The better separation efficiency of neutral amino acid may be obtained by using the resin with a lower ion exchange capacity.