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A denuder is a cylindrical or annular conduit or tube internally coated with a reagent that selectively reacts with a stable flow of gas drawn through the conduit. The gas molecules diffuse to the walls while the analyte contained in the gas is transmitted outwards via laminar flow, collected, and analyzed. Effectiveness of the system depends primarily "on a complete discrimination between the gas species and particulate matter."

Additional non-linear denuder geometries have also been tried with mixed results. Coiled configurations increased collection efficiency but lost larger particulate. A parallel multi-tube diffusion denuder has also been tried and found to increase collection efficiency. Other geometries include honeycombed, annular, and parallel plate. The development of the annular denuder in particular allowed researchers to overcome the inefficiencies of cylindrical denuders, allowing operation at larger flow rates (up to 30 times that of cylindrical denuders), shorter sampling periods, and less particle loss. (Full article...)

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