Six Kinds of Frequently Used Filter Membranes

The main function of membranes is to retain particles, bacteria and other impurities from the gas or liquid phase for the purpose of separation, purification and refinement. When choosing a filter membrane, the first consideration is chemical compatibility, like resistant to acids, alkalis, organic solvents etc. Microporous membranes are available in different materials and sizes depending on the characteristics of the target to be filtered, and are broadly divided into: mixed cellulose membranes, nylon membranes, PTFE membranes, PVDF membranes, nitrocellulose ester membranes, cellulose acetate membranes, glass fibre membranes, polyethersulfone membranes, polypropylene membranes, polycarbonate membranes and inorganic membranes.

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 degassing filtration of solvents and filtration of HPLC mobile phases. They are mainly used for the filtration of organic solvents.

Cellulose Acetate Membranes (CA) 0.2 μm membranes are well suited for the filtration of aqueous solutions, buffers, serum and media for decontamination. 0.45 μm 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.

Cellulose Nitrate Membranes (CN) are very good filter membrane materials that provide a very consistent pore size structure and wide pore size specifications. The larger pore sizes (8μm, 5μm and 3μm) are used for chemotaxis and cell retention, 0.45μm for particle collection and the smallest pore size (0.1μm) is used for ultraclean filtration of solutions and light scattering measurements. They are used for sample pre-treatment, particle detection or particle removal.

Nylon membranes (Polyamide Membranes, Nylon) have very good mechanical strength, high adsorption properties and are resistant to most organic solvents and most alkaline solutions, making them particularly 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. For the filtration of alkaline solutions and organic solvents.

PTFE Membranes (PTFE) are made of completely/completely naturally/permanently 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 extremely 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.

Glass Fiber Filters (GF) are deep filtration membranes whose main use is as a filtration layer, added directly to the 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 extend under the seal. For improved filtration throughput and continuous filtration.