1.
weighing of filters before and after coating, and
2.
checking pressure drops across the filter before and after coating. The added mass should lie between 100 and 200 μg per filter. As coatings greater than this cause increased pressure drops, probably leading to decreased pore size and lower cut points. Normal pressure drops for an 8 μm (nominal) Nucleopore filter is about 2.5 mm Hg for 10 l min-1 flow rate. The coating should result in no more than 0.2 mm Hg increase, and typical values are 0.1 mm Hg, or 4 %. Preliminary tests of the coated and uncoated filters with wet laboratory aerosols indicate negligible change in capture diameter under these conditions. If dry, ambient aerosols are available, a simple side by side test with coated and uncoated filters from the same batch (size) will confirm the coating.