DOES FILTRATION EFFICIENCY AFFECT MEASUREMENTS OF PARTICLE CHEMICAL-COMPOSITION

A direct method to measure filtration efficiency was developed and use d for the determination of the efficiency of a Nuclepore filter. This needs two equivalent filtration systems operated in sequence. The amou nt of particulate matter collected on each system is measured and intr oduced in a simple formula. The particulate masses deposited on the fi lters in each system were measured as total mass, by balance gravimetr y, and as individual elemental masses, by PIXE (particle induced X-ray emission). With this very general method it was possible to determine the efficiencies of a 0.4 mu m Nuclepore filter operated with a stack ed filter unit for particles less than 2.5 mu m in total mass and elem ental masses. The experiment showed that the efficiency of this filter is very poor for some specific elements, like sulfur, that are concen trated in very small particles.