The synthesis and development of a dual-analyte colorimetric sensor: Simultaneous estimation of Hg2+ and Fe3+

The selectivity and sensitivity of a pH stable hetarylazo dye equipped with binding sites consisting of N, S and N, O combinations, towards Hg2+ and Fe3+ over a large number of other cations including lanthanides, is described. Hg2+ and Fe3+ ions coordinate to the dye through N, S binding site forming 2:1 and 1:1 complexes, respectively. Distinct naked-eye color changes for both Hg2+ (yellow to purple) and Fe3+ (yellow to red) were quantified for simultaneous estimation of these ions. To further establish the binding and sensing phenomenon, another analogous hetarylazo dye lacking N, O combination was evaluated and found to give similar results. For practical applicability in routine life, very handy and ready-to-use paper strips coated with the dye have been prepared for the detection of Hg2+, just like the pH paper strips.