Reactive interaction of aromatic amines with dialdehyde cellulose gel

A new chromatographic method was developed for separation of amines based on their interaction with aldehyde groups in stationary phase. Expecting specific interaction with aldehyde groups through imine formation (Schiff base), we introduced dialdehyde groups to a commercial cellulose packing by periodate oxidation and examined eluting behavior of various aromatic amines. Primary amines with acid dissociation constants (pKa) greater than 6 showed no delay at pHs of 4.0-5.5, indicating the lack of interaction because of complete protonation. Primary amines with pKa less than 6 showed remarkable delays according to the amount of aldehyde groups on cellulose. The delay was dependent on the pH of eluent. The amines with pKa of 4-5.3 eluted faster at lower pH, apparently because of the change in proportion of free and protonated species. Amines with pKa less than 3.4 also showed delays but they eluted slower at lower pH. The latter behavior can be ascribed to the change in the ratio of free/protonated species of imines formed. Certain degree of steric effect was also noted, that is, compounds with a primary amino group adjacent to bulky substituents (ortho compounds) showed weaker interaction with aldehyde groups than meta- and para-isomers.