How to Choose A Syringe Filter Membrane

Start With The Solvent Not The Pore Size

Most filter selection mistakes happen because the analyst picks a pore size first and a membrane second. The membrane decides whether the filter survives the sample at all. A hydrophilic membrane in an aggressive organic solvent can swell, shed extractables or collapse, and no pore size will save the run. Decide the chemistry first, then the pore size, then the diameter.

Membrane By Membrane

Nylon is a general-purpose hydrophilic membrane that handles both aqueous and many organic mobile phases, which makes it the usual default for mixed workloads. PES gives fast flow and low protein binding on aqueous samples. MCE and CA are aqueous membranes with high flow, with CA the lower-binding of the two. RC tolerates a broad solvent range and binds little protein, so it suits samples that must be recovered intact. PTFE is the choice for aggressive solvents and acids; the hydrophobic grade needs pre-wetting for aqueous samples, while the hydrophilic grade does not. PVDF is available in both hydrophobic and hydrophilic grades and binds protein weakly. PP is a hydrophobic depth material with high dirt-holding capacity, which is why it appears in pre-filtration rather than final clarification.

Protein Binding Decides Recovery

If the analyte is a protein, a peptide or a low-concentration drug substance, a membrane that adsorbs it will lower recovery and the loss will look like a method problem. PES, RC and PVDF are the low-binding options. Nylon binds protein more strongly and is a poor choice for trace biological work even though it is convenient elsewhere.

Then Choose The Pore Size

0.45 micron is the routine pore size for protecting an HPLC column from particulates. Move to 0.22 micron for UHPLC and sub-two-micron packings, for fine precipitates, and where sterile-grade clarification is required. Coarser grades from 1.0 to 5.0 micron exist for pre-filtration of heavily loaded samples ahead of a finer stage.

Then Choose The Diameter

A 13 mm filter offers 1.09 cm2 of filtration area and suits small sample volumes. A 25 mm filter offers 2.98 cm2 and takes more volume or a heavier particle load before it blocks. If a filter blocks part way through a sample, the fix is usually a larger diameter or a pre-filtration step, not more pressure.

Watch The Pressure Limit

Syringe filters in the Easyfil range are rated to 6 bar at 23 C, and that rating depends on the housing being sealed by injection moulding rather than solvent bonding. A filter that is being forced past its rating will either burst or push unfiltered sample past the seal, and the second failure is the one that quietly ruins data.

Sterile Vented And Reusable Options

Not every filtration duty is a syringe pushing liquid through a disc. Sterifil covers sterile filtration. Vent Filter handles gas and venting duty rather than liquid samples. A reusable filter holder takes flat membrane discs and lowers consumable cost on repetitive large-volume work, at the cost of cleaning between samples and a carry-over risk that a single-use filter does not carry.