Glossary of Filtration Terms
A
ABSOLUTE PRESSURE
The pressure is above an absolute vacuum. One atmosphere (14.70 psi) is greater than gauge pressure. Symbolized as psia when the pressure is expressed in psi units.
ABSORPTION
(gen) The taking in, incorporation or reception of gases, liquids, light or heat. (phys/chem.) Penetration of one substance into the inner structure of another (cf. adsorption, in which one substance is attracted and held on the surface of another). Occurs between gas or vapor and a liquid. (pharm.) The process of movement of a drug from the site of application into the extracellular compartment of the body.
ACTIVATED CARBON
Charcoal is activated by heating to 800-900ºC to form a material of high adsorptive capacity for many gases, vapors, organics, etc. Has a large internal surface area (approx 1,000 m2/g). Commonly used in the pharmaceutical industry to remove organic contaminants. Can be used either as an additive in granular form which is then filtered out or as a filter media in a filtration device itself.
ADSORPTION
Retention of gas, liquid or solid on a surface due to positive interaction (attraction) between the surface and the molecules of the adsorbed material.
AEROBIC BACTERIA
Organisms that require oxygen to live.
AEROSOL
Dispersion of small liquid particles in a gas.
AMBIENT
Refers to “common” environmental conditions in which experiment is conducted. For example: 14.7 psia and 20º to 25ºC (room temperature).
ANAEROBIC
Organism capable of growing without the presence of oxygen.
ANISOTROPIC (ASYMMETRIC) MEMBRANE
A membrane in which the pore size and structure are not the same from one side of the membrane to the other. Such membranes are usually considered “directional” because of the difference in flow characteristics depending on which side of the membrane faces the feed stream.
ANODE
Positive pore or electrode of an electrolytic system.
AQUEOUS
Similar to or resembling water. In reference to solution made in water.
ASEPTIC
Refers to an operation performed in a sterile environment designed to prevent contamination through the introduction of bacteria.
ASSAY
Analytical procedure to determine purity or concentration of a specific substance in a mixture.
AUTOCLAVE(ING)
A chamber for sterilizing with saturated steam filters or equipment by using constant high temperature and pressure (121ºC, 15 psi). One method of (“terminal”) sterilization using saturated steam.
B
BACKPRESSURE
A backward surge of pressure from downstream to upstream of the filter. Can be the result of closing a valve or air entrapped in a liquid system.
BACKWASH
Reversal of a fluid flow through the filtration media, as an attempt to clean or “regenerate” a filter.
BACTERIA
Free living simple celled, microscopic organisms having a cell wall and characteristic shape (e.g., round, rod-like, spiral or filamentous); lack a defined nucleus.
BACTERIAL CHALLENGE
Term used when testing the bacterial retention of a filter.
BAR
A unit of pressure. One bar = 14.5 psi.
BETA RATIO
Measurement of filter retention efficiency. The ratio of particles exposed to a filter (as feed stream) to particles present in the filtrate.
BIOBURDEN
The load or level of microorganisms in a substance to be filtered.
BIOHAZARD
Biological refuse, possibly pathogenic in nature.
BIOSAFETY
Biological safety or non-toxicity of a substance to a living organism by passing tests as listed in the United States Pharmocopeia. Analogous to “chemically inert.” For filters used in biological and health care application, Plastic Class-VI tests apply, which include Systemic Injection, Intracutaneous and Implantation Tests.
BROWNIAN MOTION
The continuous zigzag motion of suspended minuscule particles. The motion is caused by impact of the molecules of the fluid upon the particles.
BUBBLE POINT PRESSURE
A test to determine the maximum pore size openings of a filter. The differential gas pressure at which a wetting liquid (usually water) is pushed out of the largest pores and a steady stream of gas bubbles is emitted from a wetted filter under specific test conditions. Used as filter integrity test with specific, validated, pressure values for specific pore-size (and type) filters.
BUNA-N
A Nitrile rubber seal compound. This is a generic term covering many formulations.
C
CAKE
Solids deposited on the filter media.
CATHODE
Negative pole or electrode of an electrolytic system.
CENTIPOISE (cP)
(N s/m2; N = Newton) A unit of absolute viscosity. One centipoises equals 0.01 stoke.
CENTISTOKE (cSt)
A unit of kinematic viscosity (m2/s). One centistokes equals 0.01 stoke.
CENTRIFUGATION
Process of separating two substances of differing densities by high-speed spinning to create centrifugal force. Typically used to separate suspended particles from liquid.
CHROMATOGRAPHY
The separation of substances in a mixture is based on their affinity for certain solvents and solid surfaces.
CLARIFICATION
To clear a liquid by filtration, by the addition of agents to precipitate solids, or by other means.
CLASS 100 ENVIRONMENT
A room environment is maintained by air conditioning and filtration so that fewer than 100 particles of size 1µm or larger are found in a cubic foot of air.
COLD STERILIZATION
Removal of all bacteria by filtration through a sterilizing grade 0.2µm absolute filter.
COLUMN
Tube or cylinder containing the chromatographic bed or stationary phase, usually in the form of beads.
COMPATIBILITY
Term used in relation to the non-reactivity of filter materials with the substance to be filtered.
CONCENTRATOR
An apparatus or method for removing some of the water from a sample to concentrate the substances dissolved or suspended in it; is usually used to concentrate solutions of biological macromolecules, e.g., proteins and nucleic acids.
CROSSFLOW (TANGENTIAL FLOW) FILTRATION
A filtration system in which the feed stream flows across the filter media and exits as a retentate stream. The retentate stream is recycled to merge into the feed stream, while a portion of it passes through the filter media, resulting in the concentration of the feed stream (referred to as concentrate).