Factors affecting retention of basic solutes in ion-exclusion chromatography using an anion-exchange column

Abstract

Retention volumes have been measured for a variety of inorganic and organic (both aliphatic and aromatic) bases on a quaternary ammonium functionalized styrene-divinylbenzene stationary phase using dilute sodium hydroxide as eluent. The retention behaviour of the inorganic bases and some of the aliphatic bases could be explained on the basis of ion-exclusion effects alone, with strong bases (which are cationic at the eluent pH) being co-eluted at the column void volume and very weak bases (which are neutral at the eluent pH) being co-eluted at the sum of the column void and inner volumes. Solutes intermediate between these extremes were eluted in order of increasing p K b1 and their retention could be varied by changing the eluent pH. A mixed retention mechanism involving hydrophobic adsorption and steric effects was observed for other aliphatic amines. Aromatic amines were found to be retained almost solely by a reversed-phase mechanism involving interaction of the solute with the unfunctionalized regions of the stationary phase. For such solutes, retention could be manipulated most easily by addition of acetonitrile to the eluent.