Fluorescence enhancement of the europium(III)-thenoyltrifluoroacetone-trioctylphosphine oxide ternary complex by gadolinium(III) and its application to the determination of europium(III)

A study of the enhancement of the fluorescence intensity of the EuIII-thenoyltrifluoroacetone (TTA)-trioctylphosphine oxide (TOPS) system by LaIII, GdIII, LuIII and YIII has been carried out in a colloidal-like suspension. Gadolinium(III) caused the largest enhancement of the fluorescence intensity. In the presence of this element the weak fluorescence of the EuIII-TTA-TOPO system was enhanced by a factor of about 18 at a pH of between 5.5 and 6.5. The excitation and emission wavelengths were 343 and 615 nm, respectively. The fluorescence intensity was linear up to 10–8M of europium; the detection limit was found to be 5 × 10–12M and the precision at 8.0 × 10–11M of europium was 1.4%. By stabilising the fluorescence with cetyltrimethylammonium bromide (CTAB), the EuIII-TTA-TOPO-GdIII system together with three other enhancing systems could be applied to the determination of trace amounts of europium in lanthanide oxides and yttrium oxide. The fluorescence intensity of the SmIII-TTA-TOPO system was also enhanced by LaIII, GdIII, LuIII and YIII. The factors influencing the fluorescence enhancement are discussed and a general mechanism involving an intermolecular transfer of energy from the enhancing complex to the fluorescing complex is proposed.