Membrane filters

Match the membrane to your liquid. Hydrophobic PTFE is the choice for gases, air and aggressive organic solvents, for example the hydrophobic PTFE membrane, 0.22 µm, 47 mm. For aqueous solutions, buffers and media, use a hydrophilic membrane: PES gives fast flow and low protein binding, as with the PES membrane, 0.22 µm, 90 mm, and cellulose acetate also binds little protein. Cellulose nitrate is the classic for microbiology and colony counting. Nylon is a broad all-rounder for aqueous and many organic samples. Unsure? sales@luminixhealth.com.

Use 0.2 or 0.22 µm when the filtrate must be sterile: it retains bacteria and is the standard for sterile filtration of buffers, media and additives. The sterile cellulose nitrate membrane, 0.2 µm, 47 mm is one example. Use 0.45 µm for clarification and particle removal, and for most microbiological colony counts in water and food testing, where the colonies must grow on the membrane: the sterile cellulose nitrate membrane, 0.45 µm is typical. Your standard method usually prescribes the pore size, so check it before you order.

A venting filter lets air in and out of a vessel, bioreactor, fermenter or storage tank while keeping microorganisms and particles out. It uses a hydrophobic membrane, usually PTFE with a 0.2 µm rating, so it stays dry and does not block when it comes into contact with moisture. Hydrophobic membrane discs, such as the PTFE membrane, 0.22 µm, can be fitted in a filter holder for small setups. For process equipment, ready-made vent capsules and cartridges are more practical; see filter cartridges and capsules. Need help sizing a vent? sales@luminixhealth.com.

Choose sterile, individually packed membranes for aseptic work such as microbiological counts and sterility testing: you take them straight from the pack onto the filter holder. The sterile cellulose acetate membrane, 0.45 µm and the sterile cellulose nitrate membrane, 0.2 µm are examples. Non-sterile membranes, like the non-sterile cellulose nitrate membrane, 0.45 µm, 47 mm, suit particle testing, analytical filtration and labs that sterilise membranes themselves. Check on the product sheet whether a membrane may be autoclaved before you do so.

The holder or funnel sets the size: the membrane has to cover the support completely and seal under the clamp or ring, so choose the diameter the holder was designed for. 47 mm and 50 mm are the common laboratory formats, for example on vacuum filtration funnels. Smaller discs of 13 or 25 mm fit compact holders; 142 and 293 mm are for large-volume pressure holders. Example: PTFE membrane with support layer, 0.22 µm, Ø 47 mm. Matching funnels are in Buchner and filter funnels. Not sure about your holder? Send us its details at sales@luminixhealth.com.

A track-etched membrane is a thin polycarbonate (PC) film in which pores are created by irradiation and etching. The result is a flat, smooth surface with straight, sharply defined pores of a uniform size. Particles stay on top of the membrane instead of inside it, which makes this membrane the usual choice for microscopy and particle analysis, where you want to see or count what was retained. For general aqueous filtration, other materials are usually more practical. Example: track-etched polycarbonate membrane, 0.45 µm, Ø 47 mm. The available pore sizes are on each product page.

They retain particles in different ways. A membrane filter has a defined pore size: particles above that size stay on the surface, which is what you need for sterile filtration, particle analysis and microbiology. Filter paper is a depth filter: particles are caught throughout the fibre structure, with a gradual rather than sharp cut-off. That makes it suitable for clarifying, gravimetric work and routine separation of precipitates. Choose a membrane when the retention has to be defined; choose paper for general filtration. See our filter paper range.

A membrane filter is the disc itself, without a syringe housing. Pore size, polymer and diameter are the specification, and the disc has to sit in a holder. Gridded membranes are for counting colonies. A membrane and a filter paper of the same diameter are not interchangeable.

Filtration holds back what is larger than the pores and lets the rest through. Paper is the ordinary laboratory filter. A membrane has a stated pore size and a polymer that must survive the solvent. A syringe filter is that membrane in a housing on a syringe. Glass fibre takes a higher dirt load. Ultrafiltration holds back macromolecules and passes salts. The pore size, the chemical compatibility and the volume are the three choices. Laboratory apparatus around filtration is indexed under ISO laboratory apparatus.

This shelf belongs to Filtration, inside Lab consumables. Luminix Health distributes this range for laboratory use.

The neighbouring shelves are Filter paper, Sintered glass filter plates & discs, Syringe filters, Filter cartridges & capsules, Glass & quartz fibre filters, Bottle-top & vacuum filtration units, Ultrafiltration & concentrators, Filtration accessories, Extraction thimbles and Dialysis tubing & devices. The category above this shelf is Filtration.

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