Separation of sulfonate and carboxylate mixtures by ion-exchange high-performance liquid chromatography

Abstract

Aromatic sulfonate and carboxylate mixtures are separated by an ion-exchange high-performance liquid chromatography method. The separation is carried out on a strong anion exchanger (quaternary amine) with a gradient of three solvents: tetrahydrofuran (THF)—water (50:50), THF—0.1 M potassium dihydrogen phosphate (pH 4.5) (50:50) and THF—0.2 M potassium dihydrogen phosphate (pH 6.5) (50:50). The change in ionic strength and pH of the mobile phase during elution results in excellent resolution of mixtures by charge and ionic group. Small variation in retention time within each class of ionic group were noted and are due to electronic and steric effects introduced by substituents on the hydrophobic part of the molecule. When applied to petroleum sulfonates, i.e., complex mixtures of alkylaryl sulfonates, this procedure gives information on the degree of sulfonation as well as the extent of variation in the structure of the alkylaryl part of the anions.