DIALYTIC CLEANUP OF ALKALINE SAMPLES PRIOR TO ION CHROMATOGRAPHIC ANALYSIS

Membrane-based devices for the neutralization of alkaline samples prior to ion chromatographic analysis are studied. These devices use a cation-exchange membrane fibre (either hollow or packed with polystyrenedivinylbenzene beads) immersed in a hydrogen ion-donating medium. As the sample is passed through the lumen of the fibre, a dialysis reaction involving exchange of sodium ions in the sample with hydrogen ions from the surrounding medium occurs, resulting in total or partial neutralization of the sample. Several hydrogen ion-donating media are evaluated on the basis of neutralization efficiency and penetration of the acid anion through the membrane. Octanesulfonic acid (OSA) at a concentration of 0.1 M gave optimal performance. Dual ion-exchange using hydrogen-form cation exchange resins slurried with water or 0.1 M OSA are also evaluated. The resin slurries provide much larger neutralization capacities than the acid solutions and are not subject to problems of penetration of the acid anion into the sample. When the resin is slurried in OSA and is stirred occasionally, the total theoretical neutralization capacity of the resin can be achieved.