Whatman PTFE PM2.5 Air Monitoring Membrane Filter, 2.0 µm, 46.2 mm, w/Support Ring, Sequentially Numbered, 50 Pack, 7592-104. Regular Price $557.06 Price $483.77. Add to Cart. Whatman 10401170, Cellulose Nitrate Membrane, plain, sterile, 0.45 um pore size, 47 mm circle (100 pcs) Regular Price $203.68 Price $176.88.