Development of a monitoring tape for hydrogen chloride gas using Metanil Yellow

Abstract

A porous cellulose tape impregnated with a processing solution that includes a pH indicator (Metanil Yellow; pH 1.2–2.3, red-yellow), glycerin and methanol is a highly sensitive means of detecting hydrogen chloride gas and is stable on exposure to light. When the sample including hydrogen chloride was passed through the tape, the colour of the tape changed from yellow to red. The degree of colour change was proportional to the concentration of hydrogen chloride gas at a constant sampling time and flow rate. The degree of colour change could be recorded by measuring the intensity of reflected light (555 nm). The detection limit was 0.1 ppm for hydrogen chloride gas with a sampling time of 40 s and a flow rate of 400 ml min^–1. No interference was observed from ethanol (1 vol.-%), propan-2-oI (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 fluoride gas (6 ppm). The relative intensities of hydrogen bromide and gaseous nitric acid were one quarter and one eighth of that of hydrogen chloride, respectively.