To Discuss the Function and Selection of Filter Membranes

Filter membranes are made using polymeric chemical materials and porogenic additives that are specially treated and applied to the support layer. Microporous membranes are one of the most widely used membranes in membrane separation technology. They are simple and fast to use and are widely used in research, food testing, chemical, nanotechnology, energy and environmental protection.

Therefore, the following factors should be taken into consideration when selecting a membrane:

  1. Material of the membrane (chemical compatibility)

When choosing a microporous filter membrane, the first consideration is chemical compatibility. Whether the membrane is resistant to acids, alkalis, organic solvents, etc.

  1. Pore size of the filter membrane

For column systems using 3 μm or larger packing, 0.45 μm needle filters or filter membranes can be used. For chromatographic systems using less than 3 μm packing, or those involving microbial growth, 0.22 μm filter membranes are recommended. For difficult turbid solutions, 1-5 μm filter membranes can be used for pre-filtration, followed by renewal filtration with the appropriate filter membrane.

  1. Material

3.1 Nylon membranes (Polyamide Membranes, Nylon) have very good mechanical strength, strong adsorption and can withstand most organic solvents and most alkaline solutions, especially suitable for the filtration of alkaline solutions. Nylon membranes are more economical than PTFE membranes when used for organic solvent filtration, such as HPLC mobile phase de-particulation filtration, and can also be used as transfer membranes. Due to the relatively high adsorption properties of nylon membranes, they are generally not recommended for media filtration, or filtration of biological samples such as protein fluids, to avoid loss of sample due to adsorption. In such cases, low adsorption cellulose acetate (CA) membranes are usually used and are more suitable.

3.2 Cellulose Acetate Membranes (CA) 0.2µm membranes are well suited for the filtration of aqueous solutions, buffers, serum and culture media for decontamination. 0.45µm membranes are well suited for the filtration of mobile phases for HPLC. Obtaining published results on membrane adsorption is difficult and is related to the substances filtered, the conditions of filtration and the assay method used as well as the fact that the membrane being assayed has not been pre-decontaminated. It is mainly used for the filtration of aqueous phase solutions.

3.3 Cellulose Nitrate Membranes (CN) are very good membrane materials, offering a very consistent pore size structure and wide pore size specifications. They are used for sample pre-treatment, particle detection or particle removal.

3.4 PTFE Membranes (PTFE) are made of completely naturally hydrophobic PTFE, which allows moist air or other gases to pass unimpeded, even at very low differential pressures, while aqueous solutions cannot pass through. PTFE membranes are chemically compatible and are capable of filtering almost all organic solvents and highly corrosive chemicals. Where aqueous solutions must be filtered through PTFE membranes, they must be pre-wetted with ethanol or isopropanol before the aqueous solution can be filtered through.

3.5 Glass Fiber Filters (GF) are deep filtration membranes whose main use is as a filter layer, added directly to the filter membrane. Note: Different filter sizes have specific requirements for the diameter of the prefilter membrane, which can be too large and cause leaks when the edges reach under the seal. For improved filtration throughput and continuous filtration.

3.6 Regenerated Cellulose Membranes (RC) are hydrophobic membranes with low non-specific adsorption, particularly suitable for particulate filtration and are chemically compatible with most organic solvents, as shown in the table below. Diameters of 50 mm and 47 mm with a pore size of 0.45 µm are used as standard for ultraclean and degas filtration of solvents and filtration of HPLC mobile phases.