Design and testing of a personal porous-metal denuder

Abstract

A personal denuder made of porous-metal disc has been designed and tested. The entire casing and substrate support are made of Teflon, and the sampling flow rate is 2 L/min. The sampler consists of a two-stage cascade impactor (having cut-off aerodynamic diameters of 9.5 and 2.0 mum, respectively) to collect liquid particles and two porous-metal discs (diameter: 2.54 cm; pore size: 100 mum; thickness: 0.317 cm) to collect basic and acidic gases, respectively. The denuder was tested for gas collection efficiency and capacity at a gas concentration of two times the permissible exposure limit (PEL, promulgated by Taiwan Institute of Occupational Safety and Health (IOSH)), with relative humidity (RH) of 80 +/- 5% and temperature of 30 +/- 3 degrees C. The test data indicate that the gas collection efficiency is high, and the capacity is sufficient for the acidic/basic gas sampling in the workplace. Using 5% (w/v, g/mL) sodium carbonate/1% (w/v) glycerol coating on the porous-metal disc, the collection efficiency is 91.2 +/- 0.26% (average +/- standard deviation), 95.08 +/- 0.06% and 100 +/- 0.04%, and the capacity is 4.47, 7.2, and 2.5 mg for HNO3, HCl and HF, respectively. The collection efficiency for NH3 for the porous-metal disc with 4% (w/v) citric acid coating is 96.39 +/- 0.13%, and the capacity is 33.6 mg.