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Scandium is used for the synthesis of a stable Sc(III)-plumbagin (PLB) complex, enabling high-sensitivity detection through fluorescence spectroscopy. In the synthesis procedure, 37.8 mg (0.2 mmol) of pure PLB was dissolved in 50.00 mL of ethanol, followed by the addition of 4.5 mL of 1000 ppm scandium standard solution (0.1 mmol) and 50.00 mL of distilled water. The pH of the mixture was adjusted to 5.5 using HCl.
The reaction mixture was stirred magnetically at 25 °C. After 30 minutes, an orange precipitate began to form, and stirring continued for 3 more hours to ensure complete complexation. The solid product was collected by filtration, washed with water and ethanol, and dried in a desiccator over P₂O₅ to constant weight. Thin-layer chromatography (TLC) was performed after each synthesis cycle to confirm purity; a single spot indicated completion. The final yield of the Sc-PLB complex was 52% based on PLB.
Characterization by UV-Vis, FT-IR, 1H/13C NMR, ESI-MS, XPS, and quantum chemical calculations confirmed the structure as [Sc(PLB)₂(H₂O)₂] with a 1:2 metal-to-ligand ratio. This complex showed strong fluorescence under optimized conditions (λex = 500 nm, λem = 600 nm) and was successfully applied in trace scandium analysis of ancient ceramics, offering a simple, accurate, and highly selective method.