Synthesis and photo-physical properties of novel Tb(III) -[Ethyl-4-hydroxy-1-(4-methoxyphenyl)−2-quinolinone-3-carboxylate] complex and luminescence sensitivity towards Malathion and Crotoxyphos pesticides

In this work, the luminescence of a novel Terbium-[Ethyl-4-hydroxy-1-(4-methoxyphenyl)−2-quinolinone-3-carboxylate] complex has been investigated as an analytical probe for pesticide detection. The sensitivity of Tb(III):L1 probe fluorescence in molar ratio 1:1 across eight pesticides was assayed in ethanol and water. The probe fluorescence has exhibited a remarkable sensitivity towards Crotoxyphos (P1) and Malathion (P2) pesticides in micromolar concentration range, where the fluorescence was quenched by gradual addition of both pesticides. Stern-Volmer studies implied static quenching dominated for P1 and P2. Using Lineweaver-Burk equation binding constants were obtained. Limit of detection (LOD) is 1.7 µM for P1 in water, 0.94, 2.68 µM for P2 in ethanol and water respectively, while the limit of quantitation (LOQ) is 5.88 µM for P1 in water, 3.1, 8.94 µM for P2 in ethanol and water, respectively. The thermodynamic parameters ΔH°, ΔS° and ΔG° were calculated to determine the nature of forces due to the interaction of the Tb(III)-L1 with P1 and P2. Finally, to assess the analytical applicability of the method, the influence of various potentially interfering anion and cations that naturally occur in water and soil were assayed. In addition, the selectivity was investigated in presence of other pesticides.