Simultaneous separation of inorganic ions and neutral organics on ion-exchange stationary phases

Abstract

Mixtures of inorganic ions and neutral organics (polars, polynuclear aromatics) were simultaneously separated on several ion-exchange stationary phases that contained both exchange- as well as reversed-phase functionality. An 8-quinolinol silica gel column and a commercial C 8/anion exchange phase were used for inorganic anion/neutral organic mixtures. Commercial C 8/weak-acid and benzene sulfonate strong-acid cation-exchange columns were employed for metal cation/neutral organic mixtures. Mobile phases were a blend of those normally used for ion-exchange separation with those generally used for reversed-phase high-performance liquid chromatography (HPLC). Both UV and conductivity detectors were used, in series. Indirect UV detection of anions on the C 8/anion column was effected with a phthalate eluent. The indirect detection could be switched off by operating at 306 nm, just above the range where phthalate absorbs; it could be switched back on again at 299 nm. Retention of metal ions on the C 8/cation column decreased with increasing mobile-phase concentration of ethylenediammonium and tartrate, as well as with increasing amounts of methanol in the mobile phase. A study of retention factor versus pH indicated that the p K a of the bound carboxylic acid is about 6.3. Efficiency was found to be better on the strong acid column than on the weak-acid C 8/cation phase. Quantitation of cations and organics was acceptable on both cation-exchange phases. Overall, this work shows the viability of simultaneous ion/neutral separation both on phases designed for mixed-mode work as well as on those intended only for ion-exchange separations. These phases permit good separation of neutral organics at lower methanol concentrations than on conventional reversed-phase columns.