How to Choose a Syringe Filter

The primary purpose of a syringe filter is to filter liquids, removing particles, precipitates, microorganisms, etc. They find widespread applications in fields such as biology, chemistry, environmental science, medicine, and pharmaceuticals, owing to their excellent filtration efficiency, convenience, and effectiveness. However, selecting the right syringe filter isn't straightforward and requires understanding the characteristics of various filter membranes and other relevant factors. This article will delve into the applications of syringe filters, the characteristics of different membrane materials, and how to make appropriate choices.

Pore Size of the Membrane

0.45μm Pore Size Membrane: Used for filtering mobile phases of standard samples, meeting general chromatographic requirements.

0.22μm Pore Size Membrane: Required for removing extremely fine particles from samples and mobile phases, as well as for microbial removal.

Diameter of the Membrane

Commonly used membrane diameters are Φ13μm and Φ25μm. Φ13μm is suitable for sample volumes of 0-10ml, while Φ25μm can be used for sample volumes of 10-100ml.

Characteristics and Applications of Commonly Used Membranes

01 Polyethersulfone (PES)

Characteristics: Hydrophilic membrane with high flow rates, low extractables, and good strength. It does not adsorb proteins or extracts, ensuring sample purity.

Applications: Designed for biochemistry, diagnostics, pharmaceuticals, and sterile filtration.

02 Mixed Cellulose Ester (MCE)

Characteristics: Uniform pore size, high porosity, thin texture, low resistance, fast filtration rate, minimal adsorption, and low cost. However, it is not resistant to organic solvents and strong acids or bases.

Applications: Filtration of aqueous solutions or sterilization of thermosensitive preparations.

03 Nylon Membrane

Characteristics: Good temperature resistance, withstands 121°C saturated steam sterilization for 30 minutes, and excellent chemical stability. It can withstand various organic and inorganic compounds such as dilute acids, dilute alkalis, alcohols, esters, oils, hydrocarbons, halogenated hydrocarbons, and organic oxidants.

Applications: Filtration of aqueous solutions and organic mobile phases.

04 Polytetrafluoroethylene (PTFE)

Characteristics: Widest chemical compatibility, withstands solvents such as DMSO, THF, DMF, dichloromethane, and chloroform.

Applications: Filtration of all organic solvents and strong acids or bases, especially those that other membranes cannot withstand.

05 Polyvinylidene Fluoride (PVDF)

Characteristics: High mechanical strength, good heat resistance, chemical stability, low protein adsorption, strong negative static electricity, and hydrophobicity. However, it cannot withstand acetone, dichloromethane, chloroform, DMSO, etc.

Applications: Hydrophobic PVDF membranes are mainly used for gas and steam filtration and filtration of high-temperature liquids. Hydrophilic PVDF membranes are mainly used for sterile treatment of tissue culture media, solutions, and filtration of high-temperature liquids.

Summary

A: Hydrophilic samples: Suitable for hydrophilic membranes, suitable for filtering solutions with water as the matrix, such as tap water and surface water, using water-based membranes (MCE) or Nylon membranes.

B: Organic and inorganic compounds (alcohols, esters, oils) samples: Suitable for Nylon membranes.

C: Protein solution samples: Use membranes with low protein adsorption, i.e., PVDF membranes.

D: Strong organic solvent samples: Suitable for hydrophobic PTFE.

E: Ion chromatography: PES membranes are generally considered suitable for filtering solutions with low inorganic ions.