Terms Used When Discussing Filters  

Terms Used When Discussing Filters

Bubblepoint Test: A test to determine the integrity and pore sixe of a filter. The differential pressure at which a steady stream of gas bubbles is emitted from a wetted filter under specific test conditions. The bubble point test measures the largest pore.

Depth Filter: A matrix of randomly distributed filters or particles creating a tortuous path of nominally rated size.

Differential Pressure: The difference in pressure between the upstream and downstream sides of the filter.

Diffusion Test: A test to determine the integrity of a filter. The test is based upon the transition from diffusional flow to bulk flow, of a gas, through a wetted filter. Either the gas or the downstream liquid, displaced by the gas, may be measured.

Downstream Side (of filter): The filtrate side of the filter.

Filter (noun): A device for carrying out filtration which consists of the filter medium and a suitable holder for constraining and supporting it in the fluid path.

Filter (verb): To pass a fluid containing particles through a filter medium whereby particles are removed from the fluid.

Filter Medium: The permeable material that removed particles from a fluid being filtered.

Filtrate: The fluid which has passed through a filter.

Filtration: The process by which particles are removed from a fluid by passing the fluid through a permeable material.

Flow Rate: Determines the volume of liquid which will flow through the filter at a fixed pressure and temperature.

Hydrophilic: Refers to a filters ability to naturally wet with water. “Water-loving” filter.

Hydrophobic: Refers to a filters lack of ability wet with water. “Water-hating” filter. Ideal for venting applications.

Integrity Test: A non-destructive test which is used to predict the functional performance of a filter. The valid use of this test requires that it be correlated to a standardized bacterial retention test. Examples: Bubblepoint test, Diffusion Test, Flow Rate Test.

Isotropic Membrane: A membrane in which the pore openings are the same diameter on both sides of the membrane.

Membrane Filter: A continuous polymeric matrix with channels of defined size.

Non-Fiber Releasing Filter: A filter which after any appropriate pretreatment, such as washing or flushing, will not release fibers into the filtrate of the product that is being filtered.

Particle: A discernible mass having an observable length, width, thickness, including particulates and bacteria.

Pore Size (absolute): The pore size at which a particle of defined size will be retained with 100% efficiency under specified test conditions, ie., a .02µm sterilizing filter will retain 10 organisms per cm² of Pseudomonus diminuta at 30 psig and ambient temperature.

Pore Size (nominal): The pore size at which a particle of defined size will be retained with an efficiency below 100% (typically 90-98%). Rating methods differ widely between manufacturers.

Pore Size Rating: The maximum diameter of a channel through the filter medium.

Porosity: The percentage of the filter area which is porous.

Sterilizing Filter: A non-fiber releasing filter which produces an effluent in which no microorganisms are demonstrable when tested by the method specified in the current edition of the United States Pharmacopeia.

Throughput: Describes the dirt handling capacity. That is, how long the liquid will continue to flow through the membrane before the membrane clogs. The lower the flow rate and throughput, the longer it takes the researcher to complete an analysis. Quality control during the manufacturing process monitors and determines a membrane’s bubblepoint, flow rate and throughput.

Upstream Side (of filter): The feed side of the filter.

Terms Used When Discussing Hybridization Membranes

Active Blotting: The transfer of macromolecules (DNA, RNA, and protein) to a substrate (a membrane filter) using a voltage gradient (electricity), vacuum, or positive pressure.

Agarose Gel: Gelatinous matrix used to separate fragments of DNA and RNA molecules according to their relative size (or molecular weight). Smaller molecules move faster than larger molecules in the gel.

Amino Acid: The “building block” or monomer, of proteins. Amino acids polymerize to form proteins.

Antibody: Protein molecule which interacts with other molecules (mostly proteins) in a highly specific manner. Antibodies are usually raised in animals (mouse, rat, rabbit), and are used to study specific proteins which are often only a fraction of a percent of a large mixture of proteins. Antibodies are often the “probes” used in western blots.

Autoradiography: The process by which the specific interaction between a radioactive “probe” and its target is usually detected. A piece of film is placed in immediate contact with a membrane filter (after probing). Areas of radioactivity on the filter expose the film (just as light exposed photographic film). These areas appear dark when the film is developed.

Blocking Agent: A substance used to prevent (or block) the nonspecific binding of probe to a membrane filter. Typical blocking ages are SDS, Denhardt’s solution, and BSA, poly (A).

Complementarity: The phenomenon which is responsible for the specific interactions between molecules of DNA, RNA, and labeled probe. Complementary DNA and RNA molecules can hybridize each other.

DNA: Deoxyribonucleic acid. This is the material of which genes are composed of. Native DNA is usually double-stranded and can be denatured to become single-stranded. Single-stranded DNA binds to hybridization membrane filters.

Electrophoresis: The process which uses voltage to separate macromolecules in a gel matrix, (usually) according to their relative size or molecular weight. Agarose and polyacrylamide gel electrophoresis are used in conjunction with transfer membrane filters.

Fractionation: The physical separation of molecules of different sizes, usually in a gel.

Hybridization: The process by which opposite strands of denatured, single-stranded DNA, or complementary strands of RNA anneal with each other to form native double-stranded DNA, RNA, or RNA-DNA duplexes. This is the process by which a probe can indentify a specific gene or fragment.

Molecular Weight: The total sum of the atomic weights of a molecule. For DNA, RNA, and (denatured) protein, a higher molecular weight means a larger molecule. Molecules with a higher molecular weight migrate slower in an elecrophoretic gel (they are usually near the top of the gel) than smaller molecules which migrate faster.

Northern Blot: The method by which RNA is fractioned electrophoretically on an agarose gel, transferred to a membrane filter and probed with radiolabelled DNA or RNA.

Passive Blotting: The process which uses diffusion to transfer (or blot) DNA or RNA to a membrane filter.

Polyacrylamide Gel: A rubbery plastic matrix used to separate proteins (and sometimes DNA or RNA), according to their relative molecular weight.

Probe: A labeled (or tagged) molecule (usually labeled with radioactivity) used to detect a specific gene (DNA) or RNA or protein. Hybridization probes are RNA or DNA.

Protein: A polymerized molecule made of amino acid subunits.

RNA: Ribonucleic acid. RNA is usually single-stranded, unless it is hybridized with single-stranded DNA, or a complementary RNA. RNA is derived from DNA.

Signal-to-Noise Ratio: The strength of a specific level of detection (e.g.; seen as a dark area on X-ray film after autoradiography, or the amount of fluorescence given off by a reporter probe) relative to the nonspecific background radiation or fluorescence. A high signal-to-noise ratio is desirable, though anything above 1.5 is often considered significant.

Southern Blot: The process by which DNA is fractioned electrophoretically on an agarose gel, denatured, transferred to a membrane filter and hybridized to a radioactive probe of DNA or RNA.

Western Blot: The process by which proteins are fractioned electrophoretically in a polyacrylamide gel, transferred by active blotting to a membrane filter and probed.