Syringe Filters
Filtration before injection to remove particulates and protect the column and injection system. Available in PTFE / PES / nylon / PVDF membranes, 0.22 / 0.45 μm pore sizes and 13 / 25 mm diameters, covering both aqueous and organic samples.
Filtration before injection to remove particulates and protect the column and injection system. Available in PTFE, PES, nylon, PVDF and other membranes, in 0.22 μm and 0.45 μm pore sizes and 13 mm and 25 mm diameters, covering both aqueous and organic samples.
Choose the membrane first: it governs compatibility and adsorption, not filtration precision
The typical consequence of the wrong membrane is not incomplete filtration butthe sample being adsorbed onto the membraneorthe membrane swelling in the solvent and its extractables entering the chromatograph. Pore size only determines what size of particle is retained; the membrane determines whether the sample is still the sample you started with.
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| Membrane | Wettability | Suitable systems | Watch out for |
|---|---|---|---|
| PTFE (hydrophobic) | Hydrophobic | Organic phases, strong acids and bases, gas filtration | Aqueous samples will not pass directly— prewet with methanol or ethanol first; the broadest chemical compatibility of any membrane |
| Hydrophilic PTFE | Hydrophilic | Both aqueous and organic | No prewetting needed and the most versatile; costs more than standard PTFE |
| PES (polyethersulfone) | Hydrophilic | Aqueous samples, buffers, cell culture media | Low protein binding and fast flow— the first choice for aqueous biological samples; not resistant to strong organic solvents |
| Nylon (NY) | Hydrophilic | Aqueous and most organic phases; broadly usable | Relatively high protein binding— not recommended for protein or peptide samples; wide solvent resistance |
| PVDF | Hydrophilic and hydrophobic versions | Aqueous and most organic phases | Low protein binding with reasonable solvent resistance;not resistant to strongly polar aprotic solvents such as acetone, DMF and DMSO |
| RC (regenerated cellulose) | Hydrophilic | Broad range, aqueous and organic | Very low adsorption and low extractables; suited to trace and formulation analysis |
| CA (cellulose acetate) | Hydrophilic | Aqueous samples, biological samples | Extremely low protein binding; poor solvent resistance, aqueous systems only |
A rule that is easily overlooked: filtering an aqueous sample through hydrophobic PTFE without prewetting sets off a chain failure — "it won't push → push harder → membrane ruptures → particulates go straight onto the column". Either switch to hydrophilic PTFE, or follow the three steps wet with methanol → displace with water → filter the sample .
Then choose pore size and diameter
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| Item | Value | How to decide |
|---|---|---|
| Pore size | 0.45 µm | The default for routine HPLC protection; adequate for analytical columns packed with 3–5 µm media |
| Pore size | 0.22 µm | For UHPLC (sub-2 µm media), narrow-bore columns, and where a sterile-grade filtrate is required; higher flow resistance and more prone to clogging |
| Diameter | 13 mm | Routine pre-injection preparation of samples < 10 mL; low hold-up volume and low sample loss |
| Diameter | 25 mm | Samples of 10–100 mL, or particle-rich samples needing more filtration area |
Bigger diameter is not better: hold-up volume inside the filter turns directly into sample loss. Use 13 mm for small, precious samples, and where necessary centrifuge out coarse particles before filtering — this markedly reduces both clogging and sample loss.
Three Most Common Mistakes
- Discard the first filtrate— the first 0.3–0.5 mL carries extractables from the membrane and housing, most noticeable in trace analysis and low-wavelength detection (< 220 nm), appearing as extra peaks or a raised baseline.
- Don't force it— normal filtration needs no more than steady pressure from the palm. If it won't push, the membrane is already blocked or the wettability is wrong; more force will rupture the membrane or burst the housing.
- One filter per sample— reuse causes cross-contamination and carryover; the cost of a filter is far below the cost of one wrong result.