Highly selective luminescence determination of terbium at the sub-ppb level with sulfonylcalix[4]arene-p-tetrasulfonate

The energy-transfer luminescence of complexes of Tb3+ with calix- (CAS), thiacalix- (TCAS), and sulfonyl-calix[4]arene-p-tetrasulfonates (SO(2)CAS), 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, WAS and SO(2)CAS, as compared to CAS, owing to the photophysical properties of the Tb3+-complexes. The detection limits for Tb3+ ion by CAS, TCAS, and SO(2)CAS ligands were estimated to be 8.2 X 10(-10) mol dm(-3) (131 ppt), 2.0 x 10(-10) mol dm(-3) (32 ppt), and 2.3 X 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 WAS complex was interfered by the presence of a 5-fold amount of other lanthanide ions, while that of the SO(2)CAS 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 SO(2)CAS. Thus, SO(2)CAS was proved to be a practical reagent for determining the Tb3+ ion at the sub-ppb level.