Development of a monitoring tape for ammonia gas in air using Rose Bengal

Abstract

A porous cellulose tape impregnated with a processing solution containing Rose Bengal, p–toluenesulfonic acid, glycerin and methanol was found to be a highly sensitive means of detecting ammonia gas, and is stable on exposure to air. When the sample including ammonia was passed through the tape, the colour of the tape changed to red. The extent of the colour change was proportional to the concentration of ammonia gas at a constant sampling time and flow rate and was recorded by measuring the intensity of the reflected light (555 nm). The tape could be used to detect down to 0.1 ppm of ammonia gas with a sampling time of 60 s and a flow rate of 400 cm³ min^–1. Reproducibility tests showed that the relative standard deviation of the relative intensity (n= 10) was 2.8% for 0.6 ppm of ammonia. No interference was observed from ethanol (1 vol.-%), trichloroethylene (1 vol.-%), acetone (1 vol.-%), carbon dioxide (4.9 vol.-%), nitrogen dioxide (100 ppm), sulfur dioxide (50 ppm), acetic acid gas (24 ppm) or hydrogen chloride gas (5 ppm). The relative intensities of ethanolamine and triethylamine were 1.04 and 1.6 times greater, respectively, than that of ammonia.