A Highly Sensitive and Selective Quinazoline-Based Colorimetric Probe for Naked-Eye Detection of Fe³⁺ Ions

A novel quinazoline-based colorimetric sensor (probe 1) that detected Fe³⁺ via naked-eye in a buffered MeOH: H₂O (8:2) solvent system within a neutral pH range was synthesized and its structure was confirmed by ¹H-NMR, ¹³C-NMR, FT-IR, and Mass spectroscopy. Its photophysical properties were also studied. The sensitivity and selectivity factor in the presence of 16 metal ions was examined by utilizing absorption titrations. Based on the selectivity test, probe 1 exhibited excellent selectivity and sensitivity toward Fe³⁺ ions among various other ions. The competitive effect indicated relatively low interference of other cations on the interaction of probe 1/Fe³⁺. To specify the sensing behavior of probe 1 to Fe ³⁺, the mole ratio method was carried out. After addition of around 500 µL of Fe³⁺, the absorption of probe1 reached saturation, and the reaction was completed. The effect of pH on the absorption and stability of probe 1 towards Fe³⁺ was examined. The pH range from 5.0 to 9.0 was appropriate for detection of Fe³⁺. To find the binding stoichiometric of the complex, Job's plot studies were carried out by varying the molar ratio of Fe³⁺. A 1:2 binding ratio was proposed. Under the optimal conditions, a good linear relationship (R² = 0.9886) was at the concentration of Fe³⁺ over the range of 50-110 µM, with a detection limit of 47.44 nM. Our quinazoline-based probe has shown good results for the quantitative determination of Fe³⁺ in samples of urine with high recovery.