Syringe Filter Selection Guide: Membrane and Pore Size

Syringe filters are a quick way to sterilise or clarify small volumes of liquid, but the wrong membrane can bind your sample, leach into it or fail in contact with a solvent. This guide covers the two choices that matter: pore size and membrane material.

Step 1: choose the pore size

Pore size	Use it for
0.22 µm (or 0.2 µm)	Sterile filtration: removes bacteria from buffers, media and reagent solutions. The standard choice when the filtered liquid must be sterile.
0.45 µm	Clarification: removes particles and precipitates, for example before HPLC or when a solution is cloudy. Not sterilising.
1–5 µm	Prefiltration of heavily loaded or viscous liquids, to stop a finer filter clogging.

A 0.22 µm filter does not remove viruses or dissolved endotoxins, and it cannot rescue a solution that was contaminated with chemicals. It removes microorganisms and particles.

Step 2: choose the membrane

Membrane	Type	Best for	Watch out for
PES (polyethersulfone)	Hydrophilic	Aqueous solutions, buffers, culture media. Fast flow and low protein binding.	Not suited to many organic solvents.
Nylon	Hydrophilic	Aqueous and many organic solutions; general HPLC sample preparation.	Binds more protein than PES; avoid strong acids.
PTFE	Hydrophobic	Organic solvents, aggressive chemicals, gases and venting.	Needs pre-wetting with alcohol before aqueous liquids will pass.
PVDF	Hydrophilic grades	Broad chemical compatibility with low protein binding; protein solutions.	Check compatibility with strong bases and some solvents.
Cellulose acetate	Hydrophilic	Aqueous protein and enzyme solutions; very low binding.	Aqueous use only.

Compatibility depends on the exact solvent, its concentration, the temperature and the filter housing as well as the membrane, so always confirm against the manufacturer’s chemical compatibility chart for anything other than water-based solutions.

Quick picks

• Sterilising a buffer, saline or other aqueous reagent: 0.22 µm PES, such as our sterile PES 0.22 µm syringe filter.
• Protein solution where sample loss matters: 0.22 µm PES, PVDF or cellulose acetate.
• Organic solvent: PTFE (or nylon, after checking the chart).
• Cloudy sample before analysis: 0.45 µm, with a prefilter if it clogs.

Filter size and volume

As a rule of thumb, 13 mm filters suit volumes up to about 10 mL and 25–33 mm filters suit up to about 100 mL of a clean aqueous solution. Viscous or particle-laden liquids clog filters sooner, so use a larger diameter or a prefilter rather than pushing harder.

Good filtration practice

1. Work in a laminar flow hood or other clean area when the result must stay sterile.
2. Open the filter pack only at the point of use and do not touch the outlet.
3. Fit the filter firmly to a luer lock syringe so it cannot pop off under pressure.
4. Push with steady, moderate pressure. Excess force can rupture the membrane; if flow stops, change the filter rather than forcing it.
5. Collect the filtrate straight into a sterile container such as a sterile glass vial, and close it at once.
6. Use each filter once and discard it.

Related: aliquoting reagents into sterile vials · PBS and buffer recipes · dilution and molarity calculator.

General guidance only; confirm suitability for your application with the filter manufacturer’s data. Union Biolabs products are supplied for laboratory research use only.