An automatic measurement of hydrogen cyanide in air by a monitoring tape method Original Research Article

An automatic monitor has been developed for hydrogen cyanide gas in air using a sensitive tape for hydrogen cyanide. It is based on color change of the tape by reaction with hydrogen cyanide. The tape containing silica gel as an absorbent and impregnated with a processing solution that includes 4,4′-bis(dimethylamino)diphenylmethane(tetrabase), copper(II) acetate, butylhydroxytoluene, glycerin and methanol was found to be a highly sensitive means of detecting hydrogen cyanide gas and it maintained stable sensitivity for at least a month in the air of a desiccator. When an air sample including hydrogen cyanide gas was passed through the tape, hydrogen cyanide was absorbed on the surface of the tape, and it reacted with copper(I) ion producing CuCN; then the tetrabase was oxidized by Cu(II) ion to form a stain. The intensity of the stain was proportional to the concentration of hydrogen cyanide at a constant sampling time and flow rate, and it could be recorded by measuring the intensity of reflecting light (555 nm). The detection limit (S/N = 3) was 0.2 ppm for hydrogen cyanide gas with a sampling time of 60 s and a flow rate of 400 ml/min. Reproducibility tests showed that the relative standard deviation of response (n = 6) was 2.2% for 5 ppm hydrogen cyanide. No response was observed from methanol (1 vol.%), acetone (1 vol.%), carbon dioxide (4.9 vol.%), carbon monoxide (100 ppm), sulfur dioxide (50 ppm), hydrogen chloride gas (8 ppm), nitrogen monoxide (50 ppm), nitrogen dioxide (4 ppm), or ammonia (40 ppm).