Membrane Filters

What is membrane filters or disc membranes?

Membrane filters are thin, semi-permeable materials that separate particles and microorganisms from liquids or gases based on their size. Disc membranes are circular, flat sheet membrane filters typically manufactured with diameters ranging from 13mm to 293mm. Their standardized circular shape makes them compatible with various filtration assemblies and holders.

Disc membrane filters provide laboratories with reliable, consistent filtration performance for critical applications. By understanding material properties, pore size ratings, and application requirements, professionals can select optimal membranes for their specific needs. 

Membrane Characteristics

Chemical compatibility: The membrane material must be compatible with the chemical being filtered to avoid structural failure.

Wettability: Hydrophilic membranes are easily wet with water and are preferred for filtering aqueous solutions. Hydrophobic membranes are recommended for gas filtration and venting, and can be wet in methanol, allowing both aqueous liquids and organic solvents to pass through.

Pore Size: Pore size provides an indication of the largest pore diameter. The bubble-point method is a common method to determine the maximum pore size and pore size distribution of membranes. 

• 0.1 µm: used for mycoplasma removal
• 0.2 or 0.22 µm: sterile filtration of aqueous solutions and organic solvents. The performance of 0.2 and 0.22μm is the same, only the difference being the designation of their pore size rating.
• 0.45 µm: clarification or particle removal of aqueous solutions and organic solvents
• 0.8 µm: coarse particulate removal and removal of bacteria

Membrane Types

PES Membrane Filters --- PES (polyethersulfone) membrane filter is made of a modified polyethersulfone polymer. Cobetter’s PES membrane filter has very low protein binding characteristics, and high liquid flow rates. PES can withstand autoclaving and is the membrane of choice for many clinical applications.

Nylon Membrane Filters --- Nylon membrane filters can be wet by water easily because they are naturally hydrophilic, providing an excellent flow rate. It also provides high strength and broad drug compatibility. Cobetter nylon membrane filters do not contain any wetting agents, detergents or surfactants, so they have low extractables, and low protein binding characteristics, often used for sterilizing and clarifying liquids. 

PVDF Membrane Filters --- PVDF(Polyvinylidene Difluoride) membranes are naturally hydrophobic. Cobetter offers both hydrophobic and hydrophilic PVDF membrane filters for a wide range of applications like aqueous and non-aggressive solvent-based. These membranes are typically low protein binding and are frequently used for sterilizing filtration.

PTFE Membrane Filters --- Cobetter offers both hydrophobic and hydrophilic PTFE (polytetrafluorethylene) membrane filters. The extreme chemical compatibility (pH 1-14) makes them very useful for they are also used for the filtration of solvents and acids or other aggressive chemicals.

MCE Membrane Filters --- MCE (Mixed cellulose ester) membrane filters are composed of cellulose acetate and cellulose nitrate. MCE membrane is biologically inert, it’s one of widely used membranes in research applications, providing superior flow rates.

PP Membrane Filters --- PP (polypropylene) membrane filter is a preferred choice for aggressive filtration applications. This plastic polymer has very good resistance to a broad range of chemicals even at high temperatures.

Glass Fiber Filters --- Glass fiber filters are porous filtration media made from fine glass microfibers, typically composed of borosilicate or quartz fibers. They are widely used in laboratory and industrial applications due to their high particle retention efficiency, chemical resistance, and thermal stability.

Typical Applications

• Microbiological Analysis: Sterility testing, microbial enumeration
• Particle Analysis: Contamination monitoring in pharmaceuticals
• Sample Preparation: Clarification before HPLC or other instruments
• Sterile Filtration: Pharmaceutical and biotech processes
• Environmental Monitoring: Air and water quality testing

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