What’s the nature of your solution to be filtered?
Gas • If you are using the membrane as a vent for a gas stream: Hydrophobic PTFE and Polyester (PETE) • For air particle collection on the membrane surface: PTFE, Silver, PP, and Glass Fiber Liquid – see next question
What is your desired end product? • Interested in particles retained on the membrane surface Polycarbonate (PCTE) and PETE for easy surface retrieval/microscopy MCE for retention and plating of bacteria from solution
• Interested in the filtered fluid MCE and Nylon have high protein-binding capacity for sterilization Cellulose Acetate, PES, PP, and PVDF have good flow rates PAN is designed for fast water purification
2. Decide an appropriate pore size
The pore size of a filter, stated in microns (aka micrometers or µm), is determined by the diameter of particles retained by the filter or by a bubble point test
• Nominal ratings are the pore size at which a particle of defined size will be retained with an efficiency below 100% (typically 90-98%) Rating methods differ widely between manufacturers
• Absolute ratings are the pore size at which a particle of defined size will be retained with 100% efficiency under specified test conditions 0.2 µm sterilizing filter will retain 10 organisms per cm² of Pseudomonus diminuta at 30 psig and ambient temperature
Fun fact: Due to viscosity differences, a 0.2 micron pore size rated membrane in liquid can retain up to 0.02 micron particles in air
What size are the particles you would like to filter?
Select a pore size (or a few pore sizes to try) that retains the desired particles - see the table for some example applications using various membrane pore sizes
0.01 um
Chemotaxis
Cytology
Separation of samples by size
Epiflourescense
0.4 um
Sterility Testing
SEM
Trace metal analysis
1.2 um
Particulate Analysis
Medical Assays
Immobilizations
10.0 um
Large Bacteria Filtration
Cancer Cell Studies
0.03 um
Liposome Extrusion
Virus Filtration
Mycoplasma removal
Bacteria Removal
0.6 um
Particle Analysis
Filtration of corrosive
solutions
2.0 um
Chemotaxis
Red Blood Cells
DNA
12.0 um
Metastasis tumor cells
Schistosoma Filtration
0.1 um
Sterilization
Clarification
HPLC Sample Preparation
0.8 um
Removal of RBC from
Plasma
Toxicity testing
5.0 um
NIOSH Methods
X-ray diffraction
Filtration of corrosive
solutions
14.0 um
Chemical Filtration
Alcohol Filtration
0.2 um
Prefilter
Microbiological analysis
Protein, enzyme filtration
Venting Application
1.0 um
Serum prefiltration
General filtration
8.0 um
Cytology
20.0 um
Chemical Filtration
General Filtration
You can also consult our Filtration Spectrum resource for reference
3. Choose the right filter disc diameter
Utilize the table to see what filter size is recommended to filter your sample volume
Diameter of Membrane
Volume of Solution
3 mm
< 1 mL
13 mm
< 5 mL
17 mm
< 12 mL
25 mm
< 100 mL
30 mm
< 120 mL
47 mm
< 1 L
≥ 90 mm
> 1 L
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We have outlined some steps to aid in the decision process: