Colorimetric cyanide detection using an azobenzene acid in aqueous solutions

An azo-based dye (I) was designed for the detection of cyanide by utilizing a new indirect method. In the presence of Cu(II), compound I could give rise to visible red-to-yellow color change. The resultant yellow solution could change to red immediately upon the addition of trace cyanide, with the detection limit of 0.15 ppm, but no changes were observed in the presence of other anions, including Cl(-), I(-), IO(3)(-), SO(4)(2-), NO(2)(-), Br(-), H(2)PO(4)(-), F(-), SCN(-), HSO(4)(-), ClO(4)(-) and CN(-), making compound I a selective and sensitive cyanide chemosensor.