summarize

1. Filter membrane material (selected according to the nature of the sample):

• Aqueous solution (aqueous phase):
  • Mixed Cellulose Ester (MCE):Low cost, suitable for conventional aqueous solutions, but not resistant to organic solvents.
  • Polyethersulfone (PES):High flow rate, low protein adsorption, suitable for biological samples (e.g. proteins, cell cultures).
  • Nylon:Acid and alkali resistant, suitable for HPLC sample pre-treatment.
• Organic solvent (organic phase):
  • Polytetrafluoroethylene (PTFE):Resistant to strong organic solvents (e.g. acetone, DMSO), hydrophobic, requires pre-wetting.
  • Polyvinylidene fluoride (PVDF):Resistant to some organic solvents, hydrophilic type can be used in aqueous phase.
• General Purpose:
  • Regenerated Cellulose (RC):Balanced performance for aqueous and medium polar organic phases.

2. Aperture size:

• 0.22 μm：Sterilization grade for removal of bacteria or particles (e.g. HPLC, cell culture).
• 0.45 μm:Routine filtration to remove larger particles (e.g. soil extracts, food samples).
• 1 μm or larger:Pre-filtration of high turbidity samples.

3. Diameter specifications:

• Common diameters: 13 mm (small volume), 25 mm (regular), 33 mm (large volume).
• Select according to the sample volume to avoid frequent changes.

4. Other characteristics:

• Sterility vs. non-sterility:Sterile pre-sterilized filters are required for cellular experiments or microbiological tests.
• Chemical compatibility:Strong acids/alkalis require PTFE or PP housing.

II. Steps for use

1. Assembly:Connect the needle filter to the syringe (Luer-Lock connector is more leak-proof) to ensure a tight seal.
2. Pre-wetting (this step is required for hydrophobic membranes):For hydrophobic membranes such as PTFE, first wet with a small amount of organic solvent (e.g. methanol).
3. Filtering:Push the syringe piston slowly to avoid excessive pressure that could rupture the filter membrane (especially for high viscosity samples such as serum).
4. Collection:The filtrate is connected directly to a clean receiver tube or chromatographic injection vial.
5. Disposal:Biohazard samples need to be sterilized along with the syringe and discarded.

III. Scope of application

• HPLC/UHPLC sample preparation:Removes particles and protects the column (commonly 0.22 μm nylon or PTFE).
• Microbial detection:Sterile filtration (0.22 μm PES or MCE) is used to decontaminate culture media or pharmaceutical solutions.
• Environmental Analysis:Filtration of suspended matter in water samples (e.g. 0.45 μm for heavy metal analysis).
• Biological experiments:Degranulation/sterilization of cell culture, serum or protein solutions.
• Food testing:Clarification of samples such as fruit juices and wines.

IV. Precautions

• Avoid overloading:High particulate content samples need to be centrifuged or pre-filtered first to prevent clogging.
• Chemical compatibility check:Strong acids (such as concentrated nitric acid) need to use PTFE material to avoid corrosion of the filter membrane.
• Pressure control:High viscosity samples (e.g., DNA solutions) can be pushed with large pore sizes or low pressure.
• Batch consistency:The standard solution is filtered through a filter and up-sampled to HPLC/MS for analysis to see if polymer is detected. Consistency with the blank test is good.

V. Frequently asked questions

• Slow filtration rate:May be due to clogged membranes or high sample viscosity, change to larger pore size or pre-filtration.
• Leakage:Check that the syringe and filter interfaces match (e.g. Luer-Slip vs. Luer-Lock).
• Background contamination:Rinse new membranes with solvent before use (especially for HPLC applications).