Liquid chromatography of alkali and alkaline-earth metal ions using octadecylsilanized silica columns modified in situ with lipophilic crown ethers

Octadecylsilanized silica (ODS) was coated with highly lipophilic crown ethers to obtain novel crown ether containing stationary phases for ion chromatography. The in situ modified ODS columns proved convenient and efficient for chromatographic separation of alkali and alkaline-earth metal ions. The retention times of alkali metal ions on the crown ether coated ODS are increased in the order Li+ < Na+ < Cs+ < Rb+ < K+ for the 18-crown-6 and 15-crown-5 derivatives and in the order Li+ < Cs+ < Rb+ < K+ < Na+ for the 12-crown-4 derivatives, being reflected in the cation-complexing properties of the crown ether rings. Simultaneous coating of more than one crown ether on ODS is possible as well, which permits easy control of the chromatographic behavior of the crown ether stationary phases. The stability (durability) of the crown ether modified ODS columns is also described