Application of the denuder technique in filter sampling of airborne chromates at ground level concentrations

Abstract

The use of the denuder technique for the preserving sampling of chromium(VI) in airborne dust at ground level (immission) concentrations was investigated. A simple denuder with activated charcoal retained by a steelwire-net cylinder was constructed. The sorption abilities of the denuder towards sulfur dioxide, which is responsible for the reduction of sampled Cr(VI) on the filter surface, were examined under various conditions. The measurements provide evidence for a laminar flow inside the denuder. At a flow rate of 100 L/h and a temperature of 27 °C the theoretical sorption value of 99.6% is reached within an experimental error of ±0.1%. A relative humidity of 19–91.5% has no influence on the sorption. In order to check if an experimental sorption value of 99.5% is sufficient to stabilize Cr(VI) on the filter surface, sampling was simulated by sucking SO2-loaded air through Teflon filters loaded with Cr(VI) containing aerosol particles with diameters of about 0.3 μm. Aerosols of two different compositions were generated by a sprayer in combination with a diffusion dryer. The particle size distributions were determined from scanning electron microscopic pictures. Chromium(VI) was eluted from the filters with an alkaline buffer and extracted from the filter eluates with a solution of a liquid anion exchanger. Chromium was determined with graphite furnace atomic absorption spectrometry. The Cr(VI) losses are between 57 and 16% depending on the composition of the aerosol particles and the “sampling” time. Realistic conditions were chosen regarding the initial Cr(VI) on the filters and the amount of sulfur dioxide which passed through the denuder.