Page 14 - Filtration Resources

If you've ever worked with a Polyamide flat sheet membrane, there's a good probability that you may have noticed some slight discoloration on the active layer side of the filter, as seen below:  And additionally, this may have caused some uneasy speculation; is it mold? contamination? time to purchase a new membrane? The good folks at Toray Membranes were able to shed some light on this common concern... literally. Brown discoloration can be due to small amounts of residual amine from the manufacturing process.  The amine, (one of the building block compounds used to create the polymer constituting  the polyamide membrane family),  can turn brown with exposure to direct light. This effect doesn't make for a pretty membrane,  but it does not affect the performance of the membrane in any way. Note: if it is in fact mold that you're seeing, you can try irrigating the area with dechlorinated water with a laboratory wash bottle to see if it lifts off.  Any rubbing of the membrane

Of all the membrane disc filter accessories that we carry, the static eliminator probably gets the most technical questions. Whereas items like the cytoclear glass slides and stainless steel membrane filter tweezers are very straightforward in their purpose and operation, how a static eliminator works may not be as intuitive. Static eliminators are used on Polycarbonate or Polyester membranes when they are going to be subject to precise analytical balance measurements that could be affected by the presence of static or dust particles on the filter. Static eliminators can perform this function in a few different ways, such as by using alternating current or by using small amounts of a radioactive element to remove electrons. The static eliminators that we carry use a naturally occurring radioactive element called Polonium-210 (It was discovered by Marie and Pierre Curie and named after Marie Curie’s homeland of Poland) in order to function. This type of static eliminator is referred to

We all know oil and water don’t mix. Same goes for acids and bases. But what about Kerosene and cellulose acetate? Or Trichloroethylene and silver? To answer these questions we have our frequently referenced Chemical Compatibility Chart for general laboratory filtration products. Since using the correct filter material is vital to the success of a separation process we are constantly expanding our knowledge base of chemicals used with our filtration products. We currently have data on over 70 chemicals and their recommendation level for filtration materials such as Polycarbonate, Nylon and PTFE. Curious about a chemical that isn’t listed yet? Just ask us about it we’ll be happy to help you out.

When counting bacteria as part of epifluorescent microscopy we generally recommend using the black polycarbonate membranes instead of cellulose membranes. This is because the black polycarbonate materials have a uniform pore size and flat surface that will retain all of the bacteria without trapping any inside of the filter. Though cellulose membranes will retain bacteria, it often will become trapped inside of the filter, where it cannot be counted.

Recently one of our customers was interested in testing Legionella bacteria and asked us how our polycarbonate membranes fit into the process mentioned on our website. If you are unfamiliar with Legionella, it is a waterborne pathogen commonly found in aerosolized waters such as cooling towers, showers, and humidifiers, and it is best known as the cause of Legionnaire’s Disease as well as Pontiac Fever. Its name originated from an outbreak that occurred at the 1976 convention of the American Legion in Philadelphia.

There are actually two areas in which membranes are used in regards to Legionella: Sample preparation and point-of-use filtration. For sample preparation the CDC (Centers for Disease Control) recommends using a 0.2 micron, 47mm polycarbonate filter to extract Legionella bacterium from potable water. Non potable water utilizes a direct plating procedure.

Point of use filtration frequently involves a device that attaches to a faucet or showerhead to eliminate Legionella. Such devices

Here is an article that does a great job of explaining what efficiency ratings mean on a filter and how they are calculated, courtesy of the American Filtration & Separation Society.  This is very useful information for filter users and purchasing agents on the practical effects the filter efficiency will have in a real world setting. You can read the whole thing here.

Over the years we have seen an increased use of filtration equipment in juice processing, particularly regarding ultrafiltration (UF) or microfiltration (MF)for the clarification of apple juice.  Since it has been demonstrated that membrane filtration can produce yields of 95%-99% - compared to only 80-94% through conventional processes – it is no wonder that filtration methods are growing in prevalence.  The greater yield combined with the reduced time and labor costs have translated to hundreds of thousands of dollars saved for juice processing plants! If you are considering juice filtration, here a couple of tips to keep in mind:

• The juice must be clear.  Of the four common types of apple juice produced – natural, crushed, clarified, and clear – only clear juice is suitable for membrane processing.
• Consider ceramic membranes.  More and more fruit juice installations are installing ceramic membranes.  While these do have  a higher cost than other materials, they do offer