THE APPLICATION OF TRIMESIC ACID TO THE DETERMINATION OF TERBIUM BY SPECTROFLUOROMETRY

A sensitive, direct spectrofluorimetric method for the trace determina tion of terbium with use of trimesic acid (TMA) has been developed. Th e reaction conditions for the fluorescence system of terbium with TMA were studied. The terbium ion can form a stable binary chelate with TM A, having a ratio of 1:1 in the pH range 3.5-6.5. The maximum excitati on and emission wavelengths are 260 nm and 545 nm for the terbium chel ate, respectively. The reaction is instantaneous and the fluorescence intensity of the terbium chelate remains stable from 0.25 to 4 h. Unde r the optimal experimental conditions the fluorescence intensity is a linear function of concentration in the range 0.0248-6.35 mu g ml(-1) of terbium. The relative standard deviation is still within +/-4% in t he presence of one-thousandfold amounts of the other lanthanide ions, and common foreign ions hardly interfere in the determination. The met hod can be employed for the determination of trace amounts of terbium in rare earth ores or oxides because of its high sensitivity and selec tivity with good reproducibility and accuracy.