Polyion ion-pair liquid chromatography : I. A new method for the regulation of the retention of ionic compounds in liquid chromatography

Abstract

A type of chemical interaction, which has received little attention in analytical and separation procedures, is introduced for the use in reversed-phase column liquid chromatography of low-molecular-weight ionic organic compounds. It is the association between a polyion and oppositely charged ions of low valency in aqueous solution. The stationary phase is a microparticulate octylsilica material. It was found that addition of a polyanion, dextran sulphate, of very high molecular weight to the mobile aqueous phase causes a drastic decrease of the chromatographic retention of divalent ammonium compounds. The results follow a retention model which assumes that the polyion associates with the sample ions in the mobile phase. Monovalent sample ions are only ver little affected by the polyion. This opens new possibilities to regulate the separation selectivity between sample ions of different valency and charge type, e.g., in ion-pair chromatography.