Solute Retention in Column Liquid Chromatography. VIII. Preparation and Properties of Metal-Modified Silica

Abstract

The method of preparation and chromatographic properties of a commercial silica lc packing, LiChrosorb SI 60, modified by surface incorporation of the cations H⁺. Li⁺, Cs⁺ NH₄ ⁺, Ag⁺, Mg²⁺ Co²⁺ Cd²⁺ and Al³⁺, are reported. The total column porosity for all columns studied lay in the range 0.52-0. 78, while the column resistance factor fell within 1060-1500. The Knox-Parcher column ratio was in all instances 14, 100, while the packing density was 0. 49 g cm⁻³. The test solutes comprised N,N-dimethylaniline, N-methylaniline, o-chloroaniline, o-nitroaniline, 2,4-dimethylaniline, m-chloroaniline, and 4-chloroaniline, for which the elution order varied substantially depending upon the cation-form silica employed. Two Ag-form columns, each heat-treated at different temperatures, provided overall the best separations. There was found to be some correlation between metal-ligand complexation constants and retentions for species where data were available, but this was not the case for the base strengths of the solutes. The columns did not deteriorate to any great extent over at least 6 weeks' continued use, and are therefore said to hold potential advantage for selective separations.