Selective optical sensing of iron(III) ions in an aqueous medium by benzochromone-based Schiff base and its application on test strips.

In this work, we designed and synthesized a novel, simple, low-cost, and effective chromone-based Schiff base ligand (HL) and its application as a chemosensor for Fe3+ detection. The structure of the synthesized sensor bears carboxylic, azomethine, and carbonyl groups which act as chelating sites for the detection of Fe3+ ions. The chemosensor HL exhibited highly selective detection of Fe3+ via a significant colour change from yellow to brown. The colour change is due to the ligand-to-metal charge-transfer (LMCT) mechanism. The sensor (HL) was characterized using UV-Vis, FTIR, NMR (1H- and 13C), and mass spectroscopy. The ligand solubility, detection condition, and sensitivity assessment suggested optimal use of DMF-water (9:1 v/v) as a working solvent at pH 7.0. Among a list of 15 metal ions screened, HL was highly selective, with instant response, towards Fe3+ ions without significant interferences with the other metal ions. The complexation ratio and association constants of HL to Fe3+ was determined by Job's plot and Benesi-Hildebrand methods, and were 2:1 and 2.24 × 103 M-1, respectively, with a detection limit of 2.86 μM. The HL probe was also applied to detect Fe3+ in real samples with acceptable performance. The simple test strips have been successfully developed and applied to the visual monitoring of Fe3+ ions with a detection limit of 68 µM. The DFT was used to examine the best interaction mode of HL with Fe metal to be Fe(III)-L or Fe(III)-2L. The chemical-reactivity and molecular electrostatic optional were figured to predict the interaction behaviour of the tested compounds.