Development of a monitoring tape for the spectrophotometric determination of sulfur dioxide in air

Abstract

A porous cellulose tape impregnated with a processing solution that includes sodium nitroprusside dihydrate, zinc formate, glycerin and methanol is a highly sensitive means of detecting sulfur dioxide in air. When the sample including sulfur dioxide was passed through the tape, sulfur dioxide was absorbed on the surface of the tape, and reacted with zinc nitroprusside to form a stain. The intensity of the stain was proportional to the concentration of sulfur dioxide 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 was 0.03 ppm for sulfur dioxide with a sampling time of 20 s and a flow rate of 400 ml/min. Reproducibility tests showed that the relative standard deviation of response (n = 8) was 0.97% for 2 ppm sulfur dioxide (TLV-TWA for sulfur dioxide is 2 ppm). No interference was observed from acetylene (0.5%), ethanol (1 vol.%), acetone (1 vol.%), trichloroethylene (1 vol.%), carbon dioxide (99.9 vol.%), carbon monoxide (103 ppm), hydrogen chloride gas (5 ppm), ammonia (40 ppm), nitrogen dioxide (50 ppm), hydrogen sulfide (20 ppm).