Water-soluble polymeric probe with dual recognition sites for the sequential colorimetric detection of cyanide and Fe (III) ions

A water-soluble polymeric probe derived from an azo-Schiff base was developed for the consecutive colorimetric sensing of CN- and Fe3+ ions in water. Herein, the synthesis of a random copolymer of N,N-dimethylacrylamide (DMA) and 3-vinylbenzaldehyde (VBA) via reversible addition-fragmentation chain transfer polymerization, [p (DMA-co-VBA, P1] is described. A post-polymerization modification reaction between the aldehyde groups of P1 and (E)-2-amino-4-((4-nitrophenyl)diazenyl)phenol in ethanol led to the target polymer, P2, with azo-Schiff base moieties. The colorimetric detection of CN- ions occurred because of the abstraction of phenolic proton of P2 by the CN- ions to form hydrazone, which was accompanied by the color change from brick-red to purple. The selective colorimetric detection of Fe3+ ions with P2 over other cations in water was also observed via the formation of a coordination complex between Fe3+ ions and azo-Schiff base ligands of P2. After the individual detection of CN- and Fe3+ was carried out, consecutive sensing studies were performed. Although Fe3+ was sequentially observed after the presence of CN- ions was noted, detection using a reverse sequence from Fe3+ to CN- was not possible because of the intense color of the resulting P2-Fe3+ complexes, which suppressed any observable color changes typically caused by the formation of hydrazone.