Membranes

Membrane filters are micro-porous plastic films with specific pore size ratings. Membranes retain particles or microorganisms larger than their pore size primarily by surface capture.

There are numerous types of membranes produced such as mixed cellulose esters, cellulose acetate, nylon, teflon both hydrophilic and hydrophobic, polycarbonate, polypropylene and PVC which are all available from Bonnet Equipment.

To choose the appropriate membrane filter users must consider the following: determine particle size to be retained or filtered. For example, 0.45 µm is the standard for E.coli bacterial removal; 0.22 µm is used to sterilise solutions; while 0.65 µm is typically used for fungi, yeast and mould separations.

Assess the chemical compatibility of the membrane with the liquid or gas to be filtered.

Depending on the test, the membrane's colour and surface pattern may be important. White membrane with a black grid is preferable for particle counting. A black membrane with a plain or gridded surface is for yeast and mould detection, using a transparent polycarbonate membrane for light-coloured particle analysis including cell studies.

All membranes are available in various pore sizes and diameters.