Impregnation of Filters for Sampling of Atmospheric Gases. The Vacuum Drying Technique

摘要

Impregnation of filters for sampling of atmospheric gases has traditionally been done by addition of the dissolved absorbing media through either dipping the filter into the absorbing solution or pouring it over the filter. To minimize blank values, to obtain a good reproducibility of the capacity of the impregnated filters, and to ensure a uniform distribution of the absorbing media on the filter, a new impregnation technique is suggested. The technique involves minimum manual handling and exposes the filters to a minimum of laboratory air. The technique is based on the principles of vacuum drying. It is applicable to any absorbing media solvable in a volative solvent. Filters are impregnated by addition of a quantitative amount of a solution of the absorbing media to each filter by a micropipette. The filters are placed on shelves inside a vacuum-tight chamber and the vacuum chamber is connected to a freeze trap. Air is removed from the chamber by a vacuum pump so the pressure in the chamber is about 1 mm Hg. The drying time of the described equipment will be 30 min. for the impregnation of 48 Whatman 41 filters of 50 mm dia., each added 350 myl of impregnation solution. No heating of the vacuum chamber is necessary to compensate the heat loss due to evaporation. (ERA citation 12:005182)