SEPARATION OF ANIONIC SURFACTANTS ON ANION-EXCHANGERS

Two anion-exchange columns, PRP-X100 and IonPac AS11, that differ in anion-exchange capacity and porous properties are evaluated for applications in the separation of anionic surfactants such as alkane sulfonates, alkyl sulfates, and linear alkylbenzene sulfonates. Retention of the anionic surfactants on the anion exchangers is due to both anion-exchange processes and interactions between the anionic surfactant and exchanger polymeric matrix. The effects of mobile phase solvent composition and counter-anion, counter-anion concentration, and mobile phase cation are evaluated. Isocratic baseline separation of alkane sulfonates and alkyl sulfates in the carbon number range of C-6 to C-12 are possible on the IonPac AS11 anion-exchange column using a 40:60 acetonitrile-water, LiOH eluent with post-column suppression and conductivity detection. Typical detection limits for alkane sulfonates and alkyl sulfates are about 14 pmol. Linear alkylbenzene sulfonate (LAS) homologs can be separated and partial separation of LAS positional isomers is also possible.