FAQ

Here's a short demonstration with Kristina explaining how to cut a Sepa CF Membrane Filter using a steel ruled die:

Is there a product or process video demonstration that you'd like to see? Let us know in the comments!

For a nice overview of some basic questions to ask before you select your liquid filtration medium, take a look at this two page paper from the American Filtration & Separations Society. It starts with clear definitions of permeability and efficiency, and then segues into the importance of compatibility between the filter material and the liquid.

One of their good points worth repeating here is that for many types of sampling there are pre-existing industrial or organizational standards to guide you. With most of our membrane, syringe, and capsule filters, you can find this information under the “Application” tab for a particular item. Our resources section is another good place to research this information. Want more help? You can always ask one of our technical personnel for added assurance.

Read the complete AFS guide here.

On the surface (no pun intended) the DK and DL series of nanofiltration (NF) membranes appear identical. They’re both thin-film membranes from Osmonics, and they are used for the same applications, such as dye concentration and acid purification, so why the separate designations?

In actuality, the difference is that the DL series has a higher flow rate, while the DK series provides higher rejection. If you look at our NF specifications page, you can see that the DK series has a rejection size of 98% -MgSO4, compared to 96% for DL. Conversely, DL has a Typical Flux/PSI of 31/100 (GFD@PSI), whereas DK rates at 22/100.

So there you have it, a small distinction perhaps, but hopefully it helps you pick the best possible item for your needs!

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 sunlight.

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 surface should be kept to an absolute minimum, as there is the possibility to scratch or damage the integrity of the membrane layer. And again, while not pretty, the mold shouldn't affect the integrity of the membrane.

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 Teflon.

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 have filters built into them, usually made of Nylon or PFT. A few years ago the American Journal of Infection Control conducted a study of these devices and found them to be extremely effective at preventing the spread of waterborne pathogens.

For more information on Legionella testing and guidelines, you can visit:

http://www.cdc.gov/legionella/files/legionellaprocedures-508.pdf
http://www.specialpathogenslab.com/SPL-Advantage/AJICFilterpaper05.pdf

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.

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 a higher flux, much longer life, and better resistance to aggressive processing and cleaning conditions.
• Know your operation.  Since fruit juices have a very low level of retained solids, the optimum mode of operation is the modified batch operation with a partial recycle of retentate.
• Not just for apples.  Other fruit and vegetables that have benefited from membrane filtration include: apricot, carrot, cherry, cranberry, grape, lemon, lime, orange, peach, passion fruit, and tomato.

References:
Ultrafiltration and Microfiltration Handbook.  Cheryan, Munir.  Technomic Publishing Company, 1998.
Microfiltration and Ultrafiltration: Principles and Applications.  Zemon, Leos & Zydney, Andrew.  Marcel Dekker, 1996.

One of the important characteristics in membrane selection is whether you want a membrane that is Hydrophobic or Hydrophilic. Here we'll define these terms, as well as provide some examples of membrane materials and applications for both types. 

Hydrophilic literally means “water loving.” Hydrophilic membranes will attract water, and in the process push away other molecules in order to allow water access to the membrane. This keeps contaminants away from the membrane allowing it stay clean and functioning for a longer period of time. Because of this trait hydrophilic membranes are especially well suited for medical applications and biological assays.

Hydrophobic on the other hand, literally means “afraid of water.” These membranes will block the passage of water and are commonly used for applications involving separation of water from other materials, such as venting gases.

Here is a helpful table that compares membrane materials and common uses for hydrophilic and hydrophobic properties: