Where it fits
A membrane disc is used in a holder, serving laboratory and low-flow point-of-use work: sterilising gas and fermenter vent air, collecting particles for aerosol sampling, and filtering samples in aggressive solvents. Unlike a pleated cartridge it has no cage or end caps — the membrane is clamped directly between sealing rings, so the condition of the holder sealing faces decides whether the filtration works at all.
Key characteristics
The membrane is biaxially stretched PTFE. Stretching builds the characteristic two-dimensional network of nodes and fibrils, giving high porosity with a uniform pore distribution. PTFE itself is essentially unreactive, so strong acids, strong alkalis and aggressive solvents are all in range — which is what makes it hard to substitute in sample preparation.
The 250 °C ceiling sits well above the 121 °C of steam autoclaving, so repeated sterilisation does not relax the membrane structure. The support layer can be PP or PET: PET is structurally stronger, PP is broader in chemical compatibility. Choose on the sample chemistry.
Choosing between options
The decisive difference between the two discs is wettability, not rating:
| Membrane | Wettability | Max temp | Typical use |
|---|---|---|---|
| PTFE (this) | Hydrophobic; aqueous needs pre-wetting | 250 °C | Gas and vent sterilisation, aerosol sampling, aggressive solvents |
| Nylon | Hydrophilic; no pre-wetting | 80 °C | HPLC sample and mobile phase prep, aqueous and alcohols |
Operation & change-out
For gas filtration use the disc dry — no wetting step. For an aqueous sample, wet the membrane first with isopropanol or ethanol and then displace with pure water, otherwise water will not enter the pores at all. Because water will not wet the membrane, a bubble point test also has to be run after wetting with a low surface tension liquid.