Solute Retention in Column Liquid Chromatography. VII. Reduction of Mass-Transfer Non-Equilibrium and Analysis Time

Abstract

Retentions are reported for the test solutes benzene and the polycyclic aromatic hydrocarbons (PAH) naphthalene, biphenyl, anthracene, and fluoranthene with columns containing mechanical mixtures of (inert diluent) Spherisorb silica + (active sorbent) Spherisorb octadecylsilyl (ODS) derivatized silica with methanol:water mobile phase. All solutes elute in one column volume with neat silica diluent packing, while both the extent of separation as well as analysis time increase as the amount of ODS phase is increased. Plots of the reduced plate height h against the reduced linear carrier velocity v show that the column efficiency with pure diluent phase is a factor of two superior to that containing neat active sorbent at v_opt. However, an anomalous rise in h is found at v less than v_opt. The capacity factors of the solutes increase linearly from zero as the amount of active phase is increased, hence limiting the permissible sample size at high packing dilution; there also occur some inversions of retention order. Dilution of lc sorbents with inert packings is thereby shown to provide quantitative control over column efficiency, analysis time and, potentially, selectivity. The technique is claimed to offer particular advantage in microbore-column liquid chromatography.