All Glass Fiber Filter Resources
Understanding Product Specifications
Adsorption
Retention of gas, liquid, solid or a dissolved substance on a surface due to positive interaction (attraction) between the surface and the molecules of the adsorbed material. The interactive forces can be electrostatic (coulombic) or non-electrostatic (dipole-dipole and hydrophobic). Adsorption to a membrane or filter device can occur in a specific manner (affinity) or non-specifically.
Autoclave(ing)
A chamber for sterilizing filters or equipment with saturated steam by using constant high temperature and pressure (commonly 121ºC, 15 psi). Many materials requiring sterilization (such as cell culture media and injectable drugs) are degraded by the heat of an autoclave and must be sterilized by other means such as filtration.
Binding Constant
Defined as the concentration of a ligand that saturates the binding of half of the available binding sites. It is a combination of the available target (receptor) and the affinity of the lignad. Also known as the dissociation constant Kd.
Coefficient of Variation (CV)
A measure of the variation that can occur between samples during a binding assay. Variation can result from liquid transfer, non-specific binding, improper washing, and anomalies with the plate. Studies indicate that the AcroWell plate has low CVs making it useful for binding assays.
Counts per Second (CPS)
Relates to the number of photons detected that are given off by the scintillant counter (radioactivity) or multilabel counter (fluorescent).
Cytotoxicity Test
A test designed to determine the biological reactivity of mammalian cell cultures following contact with the plastic or membrane with specific extracts prepared from the material under test. The procedure allows for extraction of the material at physiological to non-physiological temperatures for varying intervals.
Differential Pressure
Differential Pressure (ΔP) is the difference between the pressure in the system before the fluid reaches the filter (upstream pressure) and the system pressure after the fluid flows through the filter (downstream pressure) in a constant flow situation. As the filter begins to clog, differential pressure increases.
Effective Filtration Area (EFA)
EFA is the filter area that is available for filtration. For a given membrane, the larger the filter area, the higher the flow rate at a given initial differential pressure. Filter media and devices are available in a wide range of sizes with different EFAs.
Endotoxin
A complex molecule (lipopolysaccharide) which forms an integral part of a gram of negative bacterial cell walls and is released when the integrity of the wall is disturbed, i.e., cell division, growth, and death. Endotoxins may be released during biosynthesis of a recombinant DNA product, thus necessitating purification steps to ensure their removal.
Extractables
Substances present in the composition of the filter media or the filter manufacturing process that may be leached into the fluid as it is filtered, thereby affecting its purity. Extractables may include manufacturing debris, surfactants, and adhesives. The type and amount of extractables will vary with the type of liquid being filtered. Extractable components which can end up as contaminants may be minimized with sufficient preflushing.
Fluorescence
Light emitted from fluorophore (fluorescent molecule) as a result of excitation. The excitation wavelength (color) is different than the emission wavelength. The difference between these wavelengths is known as the strokes shift. The emitted light is detected in a specialized detector such as the Victor multi-label counter. Most fluorophores give a sample emission that is about 1 picosecond after excitation while in time-resolved fluorescence the emission occurs after a microsecond lag.
Good Manufacturing Practices (GMPs)
Regulations promulgated by the Food and Drug Administration governing the manufacture of drugs (Ref. Code of Federal Regulation 21 CFR 210 and 211), medical devices (21 CFR 820), and Large Volume Parenterals (21 CFR 212 proposed). cGMP are the current accepted standards of operation in a regulated industry.
Hold-up Volume
Volume of fluid retained in a filter and/or housing after purging the assembly with air or suitable gas. Hold-up volume is usually considered to be lost volume.
Integrity Test
A test to ensure that a sterilizing-grade filter is intact and will function as intended. Recommended integrity tests are the Forward Flow test, Bubble Point test and the Pressure Hold test. Integrity tests on sterilizing-grade filters are correlated with bacterial challenge data.
Limulus Amoeboctye Lysate (LAL) Test
An LAL gel clot test prescribed by the United States Pharmacopeia (USP) to detect and determine the level of bacterial Endotoxins in a substance. The reagent is made from the circulating blood cells (amoeboctyes) f limulus polyphemus, the horseshoe crab.
Luminescence
The emission and detection of light produced by chemical reactions or bioluminescence due directly to the enzyme light production. These enzymes can be used as labels to trace a molecule of interest. It does not require laser extraction like fluorescence because it is a result of a chemical reaction. Luminescence reactions can be carried out on membranes (blots), in a plate, or in a solution. If the reaction is being done in a 96-well form, the use of a white plate enhances the recovery of photons.
Molecular Weight Cut-off (MWCO)
Normal rating system for ultrafiltration and nanofiltration membranes. MWCO is defined as the molecular weight of solute of which the membrane retains 90%. Often defined by the molecular weight of dextran particles retained.
Operating Limits
Minimum and maximum parameters set for validation and processing pressures and temperatures.
The degree to which a fluid will pass through a permeable substance under specified conditions. The space or void volume between molecules allowing fluid flow.
pH
The pH value of an aqueous solution is a number describing the acidity or alkalinity. A pH is the negative logarithm (base 10) of the concentration of hydrogen ions (equivalents per liter). The pH value of a neutral solution is 7. An acidic solution has a pH value less than 7, while a basic solution has a pH greater than 7, up to 14.
Recovery
Ability of a filter to retain bacteria, DNA or other biomolecules from a solution. Percentage of a chemical or organism population that can be recovered after processing.
Retention
Ability of a filter to retain particles (total number or those of a specific size) suspended in a gas or liquid. In the case of ultrafiltration, refers to the ability to concentrate molecules in solution. Expressed as percent of particles or molecules originally present.
Sanitization, Sanitize
To make clean by removing dirt and other extraneous materials with soap and general disinfectant so as to reduce possibility of growth and spread of pathogenic organisms. A common sanitation agent is 70% ethanol. Bleach is also commonly used.
Sterile, Sterility, Sterilization
To make or be free of any viable microorganisms. Demonstrated by testing to show he absence of growth of microorganisms. If a high bioburden level was present prior to sterilization, pyrogens may still be present afterward.
Thickness
Thickness is typically measured with a gauge called a micrometer and is usually expressed as microns or mils. A micron is a unit of length equal to one millionth of a meter and a mil is a unit of length equal to one thousandth of an inch or .0254 millimeter.
Throughput
The amount of solution that will pass through a filter prior to clogging.
Toxicity Standards
Test to indicate adverse reactions or lethality to drugs or drug components, also used to assess biosafety of filters. Tests include appropriate combinations of direct injection, extraction, and implantation. Generally known as USP biological Reactivity Test.
Vacuum
Depression of pressure below atmospheric pressure. The maximum vacuum possible is about 63.5 cm (25 in.) of Hg.
