Filtration Membrane Discs Frequently Asked Questions
What is the difference between hydrophilic and hydrophobic membrane filters?
Hydrophilic membrane filters are typically used with water and aqueous solutions, although they can also be used with compatible non-aqueous fluids. Hydrophilic membrane filters are typically not used for air, gas or vent filtration since the filters would block flow if inadvertently wetted, for example by condensation. Hydrophobic membrane filters are typically used with compatible non-aqueous fluids. They are also commonly used as air, gas, or vent filters. Hydrophobic membrane filters are sometimes used with water or aqueous solutions and, in these applications, they must first be prewet with a low surface tension, water miscible fluid prior to use.
When should I choose a sterile or non-sterile membrane filter?
This will depend on the processing applications: If the solution is already sterilized, choose a sterile filter. If your solution is going to be run through a sterilization process, a non-sterile filter could also work.
How do I select a suitable pore size?
Pore size is determined according to the size (in microns) of the particles that we want to separate. For more than 3µm, choose a filter membrane with a pore size 0.45µm and for less than 3µm, choose a poor size of 0.22µm. The lower the membrane micron rating the finer the filtration.
How do I select the right material for the filtration membrane?
The choice of material is dependant on your application. For example, filtration membranes made of cellulose are used for colony counting and microbial analysis. Mixed cellulose ester (MCE) membranes are highly porous, pure, and have a quick wetting time. These are standard filters used in labs for air monitoring, filtration of water-based solutions, and contamination- and microbiological analysis. Cellulose acetate membranes have a low static charge and are widely used for diagnostic cytology, while cellulose nitrate membranes can be used in water purification testing and food content quality control (QC), as well as for chemotaxis assays. Membranes of polytetrafluoroethylene (PTFE) are suitable for air filtration and water quality testing. Nylon membranes can be used for HPLC preparation of samples and for filtering of aqueous solvent solutions. Membranes of polycarbonate have superior chemical resistance and are great for light and electron microscopy.