Abstract

Methods to determine terbium(III) ion in aqueous solution by measuring the enhanced fluorescence intensity of terbium(III)-terephthalic acid(TPA) complex ion have been studied. The optimum analytical conditions for pH, excitation wavelength and concentration of TPA were found to be 6.0, 260nm and <TEX>$4.0{\times}10^{-4}M$</TEX>, respectively. The fluorescence intensity of the terbium(III) complex ion was further increased with addition of trioctylphosphine oxide (TOPO). In this case Triton X-100 was used to dissolve TOPO in aqueous solution. When TOPO was used, the optimum analytical conditions for pH, excitation wavelength, and concentrations of TPA, TOPO and Triton X-100 were found to be 4.5, 285nm. <TEX>$4.0{\times}10^{-4}M$</TEX>, <TEX>$5.0{\times}10^{-5}M$</TEX>, and 0.05%, respectively. Under the optimum experimental conditions, calibration curve for Tb(III) was linear over the range from <TEX>$4.0{\times}10^{-8}M$</TEX> to <TEX>$4.0{\times}10^{-5}M$</TEX> and the detection limit was <TEX>$4.0{\times}10^{-8}M$</TEX>. When TOPO was used, the concentration range of linear response, and the detection limit were <TEX>$4.0{\times}10^{-9}M$</TEX> to <TEX>$2.0{\times}10^{-6}M$</TEX>, and <TEX>$4.0{\times}10^{-9}M$</TEX>, respectively. Effects of interferences from various cations for the determination of terbium(III) ion were also investigated.