ION-CHROMATOGRAPHIC SEPARATION OF ALKALI-METALS IN ORGANIC-SOLVENTS

Ion-exchange chromatography is a common method for the separation and determination of metal cations. Although much research has been done on improving various aspects of this technique, the use of non-aqueous eluents has received little attention. The effect of organic solvents on the retention of alkali-metal cations on a macroporous polystyrene-divinylbenzene resin was studied. The retention of alkali cations increases as the organic content in the eluent increases for most organic solvents. Methanol was an exception with a maximum retention occurring at an eluent composition of methanol-water (75:25). Since organic solvents do not solvate these cations in the same manner as water, increases in the separation factors and changes in elution order are observed, Several separations that are not possible with aqueous eluents will be shown. The effect of crown ethers in the mobile phase was also investigated. In most solvents 18-crown-6 (18C6) altered the retention of all cations. In some cases 18C6 changed elution order or improved peak shape. Separations with an organic eluent and 18C6 modifier will also be shown.