Chromogenic Detection of Fe²⁺ Using Schiff base–naphthalene-2-ol-modified Silver Nanoparticles

Abstract

Schiff base–naphthalene-2-ol (L) was synthesized by a coupling reaction between 2-hydroxy-1-naphthaldehyde and xylylenediamine in ethanol. The product was characterized by ¹H NMR, ¹³C NMR, and mass spectroscopy. L was utilized as reducing and surface functionalizing agents in the synthesis of silver nanoparticles (AgNPs) which were then characterized by high-resolution transmission electron microscopy (HR-TEM) and UV–Visible spectroscopy. The colorimetric sensitivity and metal ion selectivity of L-modified AgNPs with various cations were examined using UV–Vis spectrophotometry. The presence of Fe²⁺ induced the aggregation of AgNPs through a cooperative metal–ligand interaction, resulting in a color change from bright yellow to dark yellow with a new band at 372 nm. The interference studies confirmed the high selectivity of Fe²⁺ sensing in presence of cations as well as anions by L-modified AgNPs. A linear relationship between the change of absorption at 372 nm and concentration Fe²⁺ ranging from 1.30 × 10⁻⁵ to 1.13 × 10⁻³ M was observed with a correlation coefficient of 0.9949. The detection limit of the developed method was 1.06 × 10⁻⁶ M. The proposed method has been successfully applied for determination of Fe²⁺ content in multivitamin tablet samples. The results were in good agreement with the label claim.