The determination of hydrogen chloride in ambient air with diffusion/denuder tubes

Abstract

A manual method for the determination of hydrogen chloride in air, based on diffusion/denuder tube separation from particulate chloride aerosol is described. When air is drawn through a tube coated with a selective absorbent (sodium fluoride), separation is achieved because gaseous hydrogen chloride diffuses much more rapidly to the tube walls than particulate chloride aerosol, which passes through virtually unabsorbed. After the sampling period (the length of which depends on the concentration of gaseous hydrogen chloride expected), the sorbed hydrogen chloride is washed from the tube and measured with a highly sensitive chloride ion-selective electrode with a mercury (I) chloride membrane. The method is examined theoretically and experimentally. The experimentally derived absorption efficiencies of the diffusion/denuder tubes were > 90% and the standard deviation of the method was 0.023 μg m −3 for hydrogen chloride concentrations of 0.16–0.55 μg m −3. Interference from particulate chloride salts was negligible; this was confirmed by tests with artificially generated aerosol particles from an aerosol generator. The diffusion/denuder tubes have high capacity; level as high as 330 μg m −3 hydrogen chloride can be sampled for 60 min without affecting performance. A detection limit of (50/ t) μg m −3 can be achieved, where t is the sampling rime (min); e.g., 1μg m −3 hydrogen chloride can be detected with a sampling period of 50 min.