Binding: the property of substances to have affinity for filter media. Binding can be a desirable characteristic, as in the case of nucleic acid or protein binding on certain microporous transfer membranes, or an undesirable characteristic, as in the case of protein binding during filtration of proteinaceous solutions, sometimes leading to a loss active ingredients during filtration.
Bubble point: a measurement of the minimal air pressure needed to push liquid (often water) from the largest wetted pore of membrane while forming a steady bubble chain. The larger the pore, the less pressure required to form a stream of bubbles. Bubble point serves as an index of pore size and rates the membrane’s ability to retain particulates.
Cross-flow Filtration: in cross-flow filtration, a feed stream passes tangential to a membrane, establishing a pressure difference across the membrane. This forces some of the feed to flow through the membrane, leaving the remaining feed to continue to flow along the membrane. The use of such tangential flow will prevent thicker particulates from building up a "filter cake."
Dead-end Filtration: in dead-end filtration, all the fluid (i.e., feed) flows through the membrane and all particulates larger than the pore size of the membrane are mainly retained at its surface. In the process, the retained particulates starts to build up a "filter cake" on the surface of the membrane which has an impact on the efficiency of the process.
Depth Filters: usually characterized as those which retain particulates on the surface and within the filter matrix. All conventional fibrous filters are depth filters and are characterized by exhibiting loading capacity.
DOP Test: a measurement of the efficiency of a membrane of the production of ultrapure air based on the 0.3 um Dioctyphthalate aerosol particles passing through a membrane at a predetermined flow.
Downstream Side: the filtrate side of the membrane.
Filtrate: the fluid that has passed through the membrane.
Flow Rate: a measurement of the volume fluid (e.g., water) that passes through a membrane,given a unit of time, surface area, and pressure.
Hydrophilicity: an affinity for water. Hydrophilic membranes generally have specific surface chemistries allowing them to be wetted by water. Hydrophilic membranes can screen either liquid or gases.
Hydrophobicity: referred to be a repulsion for water. Hydrophobic membranes have little or no tendency to absorb water so that a droplet remains on the membrane surface. The degree of repellency generally depends upon filter pore size and inherent polymeric properties of the membrane material. Hydrophobic membranes transmit gas and are often used for venting.
Membrane Filters: generally described as surface filters because the filter matrix acts as a screen and retains particulates almost exclusivelyon the membrane’s surface.
Microfiltration: a method of removing contaminants from fluids or gases by passing through a microporous membrane in a pore size range from 0.1 um to 10 um. Two techniques are generally used in microfiltration, i.e., dead-end filtration and cross-flow filtration. Microfiltration is widely used in production and analytical applications including filtration of particulates from fluids and gases for different industries such as production of pure water, clarification and sterile filtration, waste water treatment, etc..
Molecular Weight Cut Off (MWCO): lowest molecular weight solute that is 90% retained by the membrane. For rapid filtration where some sample loss is acceptable, a membranehaving aMWCO the same as the molecular weight of the solute can be used. When loss of material of interest is undesirable, the membrane MWCO should be less than the molecular weight of the compound.
Nominal Rating: a measurement of the smallest particulate a membrane can retainwith greater than 90% efficiency. Ratings can differ according to challenging conditions.
Northern Blot: the method by which RNA is fractionated electrophoretically on an Agarose gel, transferred to a membrane filter and probed with radiolabelled DNA or RNA.
Prefiltration: the life of a membrane can be extended by placing a prefiltration stage upstreamto the membrane. The prefilter typically is a media that has a high loading capacity. The total particulate load challenging the membrane is considerably reduced thus allowing the membrane to operate moreefficiently.
Throughput: a practical term describing the lifespan of membrane, i.e., the total volume of a specific fluid that passes through the membrane before the membrane has to be replaced. This term is interchangeable with dirt holding or loading capacity.
Upstream Side: the feed side of the membrane.
Water Breakthrough: a measurement of the amount of pressure needed to push water through the largest pore of a dry hydrophobic membrane. The larger the pore size, the less pressure required to let water pass.
Western Blot: the process by which proteins are fractionated electrophoretically in a polyacrylamide gel, transferred by active blotting to a membrane filter and probed.