Membrane Filters, Type 113, for SamplePretreatment, Particle Testing and Chemotaxis 96 . Polyamide Membrane Filters, Type 250, for the Filtration of Alkaline Solutions and Organic . Solvents 98 . Hydrophobic PTFE Membrane . Filters, Type118, for the Filtration of Air, Gases or Chemicals 99 . Polycarbonate Track-Etch- Filters, Type230,