Enhanced Chromatographic Selectivity for Na+Ions on a Calixarene-Bonded Silica Phase

Functional esters of calixarenes, which are phenolic metacyclophanes annulated by a single methylene bridge, are immobilised onto silica particles for use in the separation of alkali metal ions by high performance liquid chromatography with conductivity detection. The immobilisation of tetrameric and hexameric calixarene ethyl esters was carried out using the triethoxy silane derivatives of p-allylcalix[n]arene ethyl esters. At an injected concentration of 10−2M, optimum selectivity for Na ions was achieved using a mobile phase of 30% MeOH/H2O with the calix[4]arene ester stationary phase. A mixture of four alkali metal chlorides is shown on injection to give a clear separation of Na+ from the other unresolved ions, the retention order being Na+ » K+ > Cs+ > Li+ = to.