The energy-transfer luminescence of complexes of Tb3+ with calix- (CAS), thiacalix- (TCAS), and sulfonylcalixarene-p-tetrasulfonates (SO2CAS), in which four p-phenolsulfonates are jointed by -CH2-, -S-, and -SO2-, respectively, was applied to an ultratrace determination of the Tb3+ ion. Based on the complexation behavior of each calix ligand, a determination procedure was established. A time-resolved measurement was conveniently employed to separate the background fluorescence from the luminescence of the calix-Tb3+ complexes. An improved sensitivity was attained by sulfur-bridged calixes, TCAS and SO2CAS, as compared to CAS, owing to the photophysical properties of the Tb3+-complexes. The detection limits for Tb3+ ion by CAS, TCAS, and SO2CAS ligands were estimated to be 8.2 × 10-10 mol dm-3 (131 ppt), 2.0 × 10-10 mol dm-3 (32 ppt), and 2.3 × 10-10 mol dm-3 (37 ppt) at S/N = 3, respectively. In terms of the selectivity, the effect of diverse coexisting ions on the luminescence intensity of the Tb3+ complexes was studied. The luminescence of the TCAS complex was interfered by the presence of a 5-fold amount of other lanthanide ions, while that of the SO2CAS complex was more tolerant for those metal ions, allowing the presence of as much as 50 to 100-fold amounts. Also, 10 to 1500-fold amounts of other common ions were tolerated by using SO2CAS. Thus, SO2CAS was proved to be a practical reagent for determining the Tb3+ ion at the sub-ppb level.
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