Nitrogen heterocycle and polynuclear hydrocarbon fluorescence and adsorption effects in the presence of silica gel. Applications in high-pressure liquid and microcolumn chromatography

Abstract

A flow-through cell packed with silica gel is used for the spectrofluorimetric examination of adsorbed states and as a detector in high-pressure liquid chromatography. The intensified fluorescence of adsorbed benzo homologues of quinoline and acridine is found to be caused by protonation of the electronically excited states by the gel. Sub-nanogram amounts of such compounds can therefore be analysed by high-pressure liquid chromatography.

In the presence of silica gel the fluorescence of polynuclear hydrocarbons is enhanced proportionally to their radiative lifetimes. The effect is disfavoured by adsorbate formation, and can therefore be employed in both adsorption and reversed-phase liquid chromatography in order to improve selectivity and sensitivity towards readily quenched fluorescences.

Microcolumns (90 × 1 mm) exhibit a ten-fold reduction in theoretical plate height compared with conventional high-pressure columns of the same adsorbent. Separations in such columns mounted on a microscope stage can be monitored by spectrofluorimetric microscopy of a silica gel particle located at the end of the column.

The techniques described are applied to heterocycles in creosotes, polynuclear hydrocarbons in gasolines and sump oil, and wood splinters, soot particles and trace amounts of pitch.