Whatman PTFE membrane filters from Cytiva's business are chemically stable and inert, making them suitable for use with aggressive organic solvents, strong acids, and alkalis. Order Product. ×. Select Model. ID. Product Name. 28415319. PTFE Membrane, TE Range (TE 35), 0.2 µm pore size, 25 mm circle (50 pcs) 28415320.