Selective Colorimetric Detection of Fe (III) Using Metallochromic Tannin-Impregnated Silica Strips

A solid state sensor tool used for determination of ferric ions (Fe+3) in an aqueous medium was developed using the environmental friendly tannin polyphenolic biomolecule as spectroscopic probe and silica plates as a host strip. The colorimetric recognition of the analyte is based on a tanna-activated silica dipstick with a determination limit in the ppm level. The best detection of Fe (III) was accomplished in a pH range from 3.2 to 8.8. The metallochromic tannin-impregnated silica diagnostic tool provided an instant color alteration from yellow to dark purple upon immersion in an aqueous environment of ferric cation as was demonstrated by the coloration measurements. This color shift is proportionally correlated with increasing the ferric concentration. Both qualitative and quantitative studies were performed. The sensor demonstrated high selectivity to Fe (III), while no color change was monitored for other metals. The recognition mechanism of ferric occurs via tannic (polyphenolic)-Fe (III) polydentate complex creation. Different spectroscopic techniques, including scanning electron microscope, energy dispersive X-ray spectroscopy as well as elemental mapping were utilized to characterize the tannic-Fe (III) complex formation on the silica dipstick.