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, ΔI_F=AC_Ln+B, was given. The relationships of A (defined as sensitivity factor) with some physical parameters (atomic number Z, ionic radius γ_±, standard redox potential E^o and hydration enthalpy ΔH_hyd) 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_±, E^o and ΔH_hyd should originate in the special features of Ln³⁺ electronic configurations Xe]4fⁿ (n=0–14). Using the proposed model of Ln³⁺–luminol interaction, lgΔI_F/(I_Fo–ΔI_F)]=rlgLn]+lg k, the association constant k was obtained over the range of 1.95×10⁶–2.63×10⁷ L mol^?1.