Believe it or not, in most cases end-users tend to use the blue separator paper instead of the membrane because the separator paper has the physical qualities that make it look more like a typical depth filter than the Track-Etch filter membrane.

Always remember that the filter membrane is usually opaque or translucent and is generally white or white with a yellow or green tint to it. The separator paper is usually blue or imprinted and should not be used for filtration.

Another reason for lack of filtration is due to particle loading on the membrane that would cause the filter to plug. Because Sterlitech Track-Etch filter membranes are made of plastic with cylindrical pores, they capture 100% of all particles larger than the pore size. Therefore, they have a higher incidence of plugging due to their high level of capturability. It is highly recommended that unless the end-user is capturing particles on the surface for analysis that a glass fiber prefilter is used on top of the track-etch membrane. The glass fiber prefilter will capture most of the larger particulate, thereby keeping it from loading up on the surface of the membrane and plugging it.

The use of a mesh spacer (drain disks) is also helpful for maximizing flow. A mesh spacer is set under the membrane and on top of the filter holder. The mesh spacer lifts the membrane off the mostly solid filter holder surface, allowing increased filtration by allowing tangential flow to occur. This is particularly applicable with stainless steel supports.