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MCE Membranes

Hydrophilic MCE membranes utilize a mixture of cellulose nitrate/acetate fibers to deliver superior flow rates, precise pores, and high protein binding capacity; ideal for particle monitoring, diagnostic kit manufacturing, and microbiology applications.

Many microbiological techniques include colony counting after incubation as the standard method of quantification. Gridded filters have clearly defined grid lines spaced at 3.1 mm intervals. The special ink used is nontoxic and completely free from bacterial growth inhibitors. White gridded disks are designed for the recovery and retention of E. Coli bacteria in water/waste-water analysis as well as other microbiological tests. Black mixed cellulose esters(MCE) are available plain for automatic colony counting applications, as well as gridded to assist in manual counting procedures. Black MCE membranes provide contrast between residue or cell colors and the filter without having to counter-stain the membrane.

Additional Resources:

MaterialFeaturesApplicationsPore Size (μm)
Advantec MCE Membrane Filters, Non-Sterile

Superior flow rates, Triton-free, autoclaveable, quick wetting time

Filter sterilizing biological fluids, microbiology, contamination analysis, air monitoring, can be transparentized to view collected particles, gridded filters available for quantifying microbial growth

0.1-8.0
Advantec MCE Membrane Filters, Sterile

Triton-free, superior flow rates, autoclaveable, pre-sterilized

Filter sterilizing biological fluids, microbiology, contamination analysis, air monitoring, can be transparentized to view collected particles, gridded filters available for quantifying microbial growth

0.2-1.0
Sterlitech Cellulose Nitrate Filter, Sterile

 

High protein binding, Triton-free, sterile options available, good thermal stability, adsorptive

 

Microdialysis of DNA and proteins, sterilizing filtration, air monitoring, particle monitoring, particle removal, and bioassays, clarification of aqueous solutions, particle analysis, microbiology analysis, retention of yeasts, molds, and algae

0.22-1.0
Sterlitech MCE Membrane Filters, Sterile

High protein binding, Triton-free, sterile options available, adsorptive

Microdialysis of DNA and proteins, sterilizing filtration, air monitoring, particle monitoring, particle removal, and bioassays, clarification of aqueous solutions, particle analysis, microbiology analysis, retention of yeasts, molds, and algae

0.22-1.0

Frequently Asked Questions


The pores of microporous membrane filters act as small capillaries.  When hydrophilic membranes come into contact with water, capillary action associated with surface tension forces causes the water to spontaneously enter and fill the pores.  In this manner, the membranes are easily wetted and allow the bulk flow of water through the pores.  Once wetted, hydrophilic membranes will not allow the bulk flow of air or other gasses, unless they are applied at pressures greater than the membrane’s bubble point.

Hydrophilic membrane filters are typically used with water and aqueous solutions.  They can also be used with compatible non-aqueous fluids.  Hydrophilic membrane filters are typically not used for air, gas or vent filtration since the filters would block flow if inadvertently wetted, by condensation for example.

When hydrophobic membranes come into contact with water, surface tension forces act to repel the water from the pores.  Water will not enter the pores and the membranes will act as a barrier to water flow, unless the water is applied at pressures greater than the membrane’s water entry pressure.  Low surface tension fluids, such as alcohols, can spontaneously enter and fill the pores of hydrophobic membranes.  Once all the air in the pores is displaced, there are no longer any surface tension forces and water can easily enter the pores, displace the low surface tension fluid, and pass through the membrane.  The membrane will then allow bulk flow of water for as long as the pore remain water filled.  If the membrane is allowed to dry (i.e. air enters the pores), then it must be pre-wet with a low surface tension fluid again prior to use with water.

Hydrophobic membrane filters are typically used with compatible non-aqueous fluids.  They are also commonly used as air, gas, or vent filters.  Hydrophobic membrane filters are sometimes used with water or aqueous solutions; and, in these applications, they must first be prewet with a low surface tension, water miscible fluid prior to use.

MCE membranes feature fast flow rates, a high protein binding capacity, and great thermal stability, making them a staple for many environmental and biological laboratories. Furthermore, they are available as presterilized, individually wrapped membranes, and can include a gridded pattern for quantifying microbial growth.

Q. What is the maximum temperature for the different filter membranes?
A. The maximum operating temperatures for Sterlitech filter membranes are listed below.

 

*5.0um and 8.0um - max temp is 180°C

Yes, the MCE membrane filters do have a limited shelf life. The MCE membranes necessarily contain wetting agents that improve performance by ensuring good wettability with water and aqueous solutions. Prolonged storage of the MCE membrane filters, especially after the packaging has been opened, may allow the wetting agents to degrade. For optimal filter performance, it is recommended that the MCE filters be consumed within one year from being received.

Ideally, nitrocellulose (NC) membranes would be made entirely of nitrocellulose polymer. However, almost all commercially available filtration grade membrane filters labeled as “nitrocellulose” are actually composed of membranes made with a mixture of nitrocellulose and cellulose acetate polymers. This is because pure nitrocellulose membrane filters are very difficult to manufacture with acceptable characteristics. 

In an effort to provide clarity to consumers, some manufactures refer to membranes containing a mixture of nitrocellulose and cellulose acetate polymers as mixed cellulose esters (MCE) membranes. In almost all filtration applications, mixed cellulose esters (MCE) membrane filters are equivalent to nitrocellulose (NC) membrane filters.

Q. What is the difference between nominal and absolute pore size ratings?

Nominal pore size ratings are provided as a general indication of filter retention.  It is understood that some quantity of particles greater than, and equal to, the nominal pore size ratings will pass through the filters into the filtrate.  Some manufactures may associate nominal pore size ratings with percentage filtration efficiencies. Nominal pore size ratings vary from manufacturer to manufacturer and, consequently, are not necessarily equivalent. Filters from different manufactures with similar nominal pore size ratings may not actually exhibit similar retention characteristics.

Absolute pore size ratings are typically based on retention studies performed using challenge suspensions of standard microorganism cultures or particles of known size. Absolute pore size ratings represent the size of the smallest microorganisms or particles completely retained during these studies. Absolute pore size ratings are almost always correlated to bubble point specifications that are used for quality control during membrane manufacturing. For the most part, absolute pore size ratings, especially those based on microbial retention, are comparable from manufacturer to manufacturer. There is more uncertainty for absolute pore size ratings based on particle retention studies, especially for pore size ratings <0.2µm, since there are no standard methods for these studies.

Regardless of pore size ratings, it is important to understand that application conditions do influence particle retention. Even filters with absolute pore size ratings can be operated in conditions that will allow unexpectedly sized particles to pass.


Unfortunately, in most instances, we are unable to supply the MCE membrane filters with custom diameters. Please inquire with your Sterlitech sales representative about alternatives.

The pore size refers to the diameter of the individual pores in a membrane filter.   Pore size is typically specified in micrometers (µm).   Most membranes and filter media actually contain a distribution of pore sizes.  Nominal pore size ratings typically refer to the predominant pore size of a filtration media; pores larger and smaller than the nominal rating may be present.  Absolute pore size ratings typically refer to the largest pore size of a membrane and it is expected that all pores will be equal to or smaller than the absolute rating.

For the polycarbonate track-etch (PCTE) and polyester track-etch (PETE) membrane filters, porosity is the percent of the total surface area occupied by the pores; it typically ranges from <1% to 16%.  For the other membrane filters, porosity is the percent of the total volume occupied by the pores; it typically ranges from 40 to 80%.

Sterile mixed cellulose esters (MCE) membrane filters are used in vast quantities for microbiological studies across many industries and are manufactured in very high volumes to accommodate this demand.  Economies of scale and process automation allow the sterile MCE membrane filters to be offered at lower pack costs compared to non-sterile MCE membrane filters.  Non-sterile MCE filters are used much less frequently, necessitating less efficient, smaller volume manufacturing runs and packaging methods.  Consequently, the non-sterile MCE membrane filters have intrinsically greater manufacturing costs and must be offered at higher prices.

You can find the Sterlitech compatibility guide.  It is important to realize that application conditions, such as operating temperature, affect compatibility.  Please contact us at [email protected] if you need assistance.

The grid dimensions are 3mm x 3mm. The average number of squares for a 47 mm disc filter is 185.

The bubble point is the minimum amount of pressure required to push air bubbles through the largest pore of a wet membrane.  The bubble point is inversely proportional to the pore diameter, as the pore diameter decreases the bubble point increases and vice versa.

Retention efficiency of membrane filters can be directly measured by challenging the filters with suspensions of standard microorganism cultures or particles of known size.  Unfortunately, such efficiency testing is necessarily destructive.  However, since retention characteristics are dependent on pore size, it is possible to correlate destructive challenge testing results to non-destructive membrane bubble point tests.  In this manner, the relationship between membrane pore size and membrane bubble point is empirically determined.  Typically, a minimum bubble point can be determined and specified for a particular pore size rating.  The bubble point specification is then used for quality control during membrane manufacture.  The bubble point can also be used by the consumer as a nondestructive test to verify membrane integrity before and/or after use.    

Depth filters are constructed with relatively thick filtration media and typically have nominal pore size ratings >1µm. Due to their large void volume, they capture significant amounts of particulate within their pore structure.
Membrane filters are typically composed of polymers that have been chemically processed, resulting in highly porous thin films with microscopic pore structures. Membrane filters typically have absolute pore size ratings <1µm, with some exceptions. Because of their very fine pore structure, membrane filters tend to trap the majority of particles on the surface. However, smaller particles with diameters near or below the pore size rating can be captured within the membrane or pass through the membrane.

membrane filters vs separator papers

To ensure ease of use, the membrane filters as stacked in their packaging are interleafed with layers of separator paper.  In most cases, the membrane filters will be white in color except for the track-etch membranes which are colorless and translucent.  In some special cases, the membranes will be dyed dark grey to black in appearance.  In all cases, the separator paper will be a different color than the membrane and is usually not white.  Please contact us at [email protected] if you need assistance.