Study on the luminescence behavior of lanthanide ions using luminol as probe

Using luminol as the probe, the luminescence behavior of trivalent lanthanide ions (Ln3+=La3+, Ce3+, Pr3+, Nd3+, Sm3+, Eu3+, Gd3+, Tb3+, Dy3+, Ho3+, Er3+, Tm3+, Yb3+ and Lu3+) in aqueous solution was first investigated by fluorescence, and the sensitivity enhanced by 3–5 orders of magnitude compared with the Ln3+ intrinsic fluorescence. It was found that Ln3+ with luminol could form a 1:1 association complex which remarkably enhanced the fluorescence signal of luminol. The increment of fluorescence intensity was proportional to the concentration of Ln3+ in the range of 1.0–70.0 nmol L−1, and the linear correlation equation, ΔIF=ACLn+B, was given. The relationships of A (defined as sensitivity factor) with some physical parameters (atomic number Z, ionic radius γ±, standard redox potential Eo and hydration enthalpy ΔHhyd) were discussed. The good symmetry of A vs. Z plot for light lanthanides (LLG) and the heavy lanthanides (HLG) and linear relations of A with Z, γ±, Eo and ΔHhyd should originate in the special features of Ln3+ electronic configurations [Xe]4fn (n=0–14). Using the proposed model of Ln3+–luminol interaction, lg[ΔIF/(IFo–ΔIF)]=rlg[Ln]+lg k, the association constant k was obtained over the range of 1.95×106–2.63×107 L mol−1.