Chromotropic acid-activated silver nanoparticles: a convenient colorimetric sensor for selective determination of divalent and trivalent iron ions

Iron ions play a crucial role in various biological, environmental, and industrial processes, making their quick and on-site detection in aqueous solutions a significant analytical challenge. This study presents a simultaneous colorimetric detection method for Fe(II) and Fe(III) ions in aqueous solutions using silver nanoparticles (AgNPs) functionalized with chromotropic acid (CTA). The detection of Fe(II) and Fe(III) ions based on CTA-AgNPs was monitored both visually and through ultraviolet–visible spectrophotometry (UV–vis). We discover a variation in nanoparticles size and absorption with their interaction with different ions, which allow us to determine analytical parameters such as the detection and quantification limits. This colorimetric system showed excellent selectivity to the detection of Fe(II) and Fe(III) ions, even in the presence of other metal cations that could potentially interfere the analysis. This approach offers a robust and efficient method for detecting iron ions, with potential applications in environmental monitoring and industrial processes.