Fiber optic sensing of cyanides in solutions

A novel sol-gel technique was used to immobilize malachite green ions (MG⁺) in stable, optically transparent, porous silica gel films. A simple and sensitive method was developed for the detection of cyanides in solutions using spectrophotometry to measure changes caused by cyanide ions (CN^-) in the absorption spectra of the green-colored silica gel films. After reaction with cyanide ions, the absorption spectra of the films changed with a typical decrease in absorbance at 620 nm. On the basis of the absorption spectra of the films, a portable and easy to use fiber optic cyanide film sensor was fabricated. Decolorization undergone by the green-colored gel films, as they were exposed to cyanide ions, was detected through a fiber. Preliminary results indicate concentrations on the order of a few ppm are detected using the fiber optic sensor.