Spectrofluorimetric determination of terbium with terephthalic acid

A spectrofluorimetric method has been developed for the determination of terbium(III) based on the formation of a complex with terephthalic acid [benzene-1,4-dicarboxylic acid (TPA)] in slighdy acidic aqueous solution in the presence of gelatin. Terbium ion can form a stable complex with TPA with the stoichiometry of 1:2. The best excitation and maximum emission wavelengths are observed at 260 run and 545 nm, respectively. The fluorescence intensity of terbium complex gets the strongest within 20 min and remains stable up to 10 h, and it is proportional to terbium(III) concentration in the range of 4.0× 10-5-1.6×10-7 mol.L-1 under the optimum conditions. The fluorescence system has good selectivity, sensitivity and stability. The relative standard deviation is still within ±4% in the presence of 1200-fold amounts of the other lanthanide ions when the concentration of terbium(III) is 1.0×10-6 mol.L-1 and common co-existing ions hardly interfere the determination. It has been applied to the direct fluorimetric determination of trace terbium (III) in rare earth ores and oxides.