Membrane Thickness: 150-190µm. pH Range: 1-14. PTFE Syringe Filters, iPure™ brand, hydrophobic, low cost, disposable. With 0.22µm PTFE (Polytetrafluoroethylene or Teflon) hydrophobic membranes in 13mm polypropylene housings, these economical filters are compatible with organic solvents, acids and bases but not recommended for aqueous solutions.