Solid-Phase Lanthanide Luminescence Detection in Liquid Chromatography

Terbium ions are immobilized on silica gel through ethylenediaminetetraacetic acid (EDTA) or diethylenetriaminepentaacetic acid (DTPA) ligands. The resulting materials are utilized as solid-phase detection systems in liquid chromatography. Terbium(III) luminescence is observed when organic compounds that can transfer energy to Tb(III) by an intramolecular process are present. Peak tailing caused by slow dissociation of transferring compounds from the Tb(III) is significantly reduced if potassium acetate is added to the mobile phase. The solid phases slowly turn a bluish-green color unless triethylenetetraamine is added to the mobile phase. The color change is believed to be caused by bonding of trace amounts of transition metal ions to the solid phase. Detection of carboxylic acid-containing compounds such as indole-2-carboxylic acid, indole-3-acetic acid, 5-methoxyindole-2-carboxylic acid, kynurenic acid, and quinolinic acid is more sensitive with the Tb−DTPA phase than the Tb−EDTA phase, whereas detection of salicylic acid is more sensitive with Tb−EDTA than with Tb−DTPA. The use of time-resolved detection methods significantly enhances the sensitivity. Linearity, reproducibility, limits of detection, and chromatographic separations are examined for several compounds.