LUMINESCENCE DETECTION OF RARE-EARTH IONS BY ENERGY-TRANSFER FROM COUNTERANION TO CROWN ETHER LANTHANIDE ION COMPLEXES

A novel method has been developed to enhance the sensitivity and selectivity of the luminescence detection for lanthanide ions. In this method, the lanthanide ion, crown ether, and benzoate were compartmentalized into an ion pair complex in order to eliminate the quenching and to induce the energy transfer so that the luminescence detection for the lanthanide ions can be selectively enhanced. The molecular organization Is achieved by using a crown ether such as 18-crown-6 or 15-crown-5 as the synergistic extracting agent and benzoate as the counterion to selectively extract the rare-earth ions from water into an organic solvent where they are subsequently determined by luminescence technique. Compared to lanthanide ions In aqueous solutions, the luminescence intensity of the extracted ion pair complexes is substantially enhanced. The luminescence intensities of the Tb3+, Eu3+, and Dy3+ ions were enhanced up to 4 times when they were extracted into ethyl acetate or into chloroform. This is because in water, the metal ions are quenched by the high-frequency vibrations of the OH group and this quenching Is eliminated when they are extracted into the organic solvent. In addition, the measured luminescence intensity can be further enhanced up to 17 times by performing the measurement at the excitation wavelength where the lanthanide ions were not excited directly but indirectly through the energy transfer from the counterion (i.e., benzoate). The total enhancement by the extraction and energy transfer processes can, therefore, be up to 67 times. The mechanism of energy transfer and the use of this technique to measure the selective extractions of Tb3+, Eu3+, and Dy3+ ions are discussed. © 1990, American Chemical Society. All rights reserved.