Aluminum Oxide Membrane Filters, 0.2 Micron, 25mm, 50/pk

Yes, you can use the AO membrane disc filters in the stirred cells. These disk filters are very brittle and must be handled with an abundance of care to avoid breakage. Use membrane tweezers  to carefully place the disk filter on the surface of the support disk and then install the support disk in the stirred cell body.

The Sterlitech aluminum oxide membrane filters are not available with perimeter support rings.  However, when handled with care, they are suitable alternatives to competitive aluminum oxide membrane filters with ring supports. 

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%.

The aluminum oxide membrane filters can be readily dissolved with sodium hydroxide solutions at 1M concentration or higher.  The time required to dissolve the membrane can be reduced by elevating the temperature and/or increasing the concentration.

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.

Sample packs allow the customer to purchase small quantities of membrane filters at nominal cost, with various diameters and pore sizes as selected.  This allows the customer to preform trials as needed to determine the optimal filter for their application before committing to purchasing standard pack quantities.

 

In most cases, membrane filter samples can be purchased in sizes that are not listed in the standard sample packs.  Please contact us at [email protected] to inquire about availability and pricing.

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.

• Silver Membrane Filters:  These are the best choice for reflectance IR spectroscopy, but cannot be used for transmission IR spectroscopy.  
• Aluminum Oxide Membrane Filters: Depending on the spectral range, these are a good choice for transmission IR spectroscopy, but they are a poor choice for reflectance IR spectroscopy. These filters are extremely brittle and will fracture if subjected to bending. They cannot be handled with fingers; membrane tweezers must be used. 
• Glass Microfiber Filters: Depending on the spectral range, these filters can be used for both reflectance and transmission IR spectroscopy. The paper does not specify any particular pore sizes; however, most of our offerings should have good efficiency with ≥5-micron sized particles. For good light transmission, I would guess that a thin, binder- less filter media would be best, such as Grade C or GC-50.  Gold-Coated Polyester Track-Etch Filters: Gold coated polyester track-etch filters have essentially the same spectral properties as gold-coated polycarbonate track-etch filters; but they are inherently hydrophilic and, consequently, much more convenient for use with water samples. These are a good choice for reflectance IR spectroscopy, but cannot be used for transmission IR spectroscopy.