The diameter of the largest hard spherical particle that will pass through a filter under specified test conditions. A filter with an absolute rating will retain 100% of particles at or above that size.

The adhesion of molecules (gas, liquid, or dissolved solid) to a surface. In filtration, adsorption can cause undesirable loss of target compounds — particularly relevant when selecting low-protein-binding membranes.

Any solution in which water is the primary solvent. Many membrane types are optimized for aqueous solutions and may not be compatible with organic solvents without pre-wetting.

A membrane with a gradient pore structure — a fine, dense skin on one side and a more open, porous support layer on the other. This design maximizes flow rate while maintaining tight retention at the active surface.

A pressurized device used for steam sterilization at high temperatures (typically 121°C). Not all filter materials are autoclavable; PTFE and certain nylons can typically withstand the process while others may degrade.

The ability of a filter membrane to remove bacterial organisms from a solution. Membranes with a pore size of 0.2 µm or smaller are typically considered sterilizing-grade for this purpose.

The number of microorganisms present in or on a material before sterilization. Monitoring bioburden helps determine the appropriate filtration strategy and validates filter performance.

An integrity test for wetted membranes. Gas pressure is applied to a wetted filter; the pressure at which a continuous stream of bubbles is first observed indicates the largest pore size present in the membrane.

A solution that resists changes in pH, commonly used to maintain stable conditions during biological filtration, chromatography, and protein purification processes.

A self-contained filtration unit with an integrated membrane and housing. Designed for inline use without a separate filter holder; available in sterile, single-use configurations for process filtration.

A cylindrical filter element designed to fit into a reusable housing. Used in high-throughput applications requiring continuous or large-volume flow at production scale.

A hydrophilic membrane material derived from cellulose. Low protein binding, suitable for biological fluids and aqueous solutions. Not compatible with strong acids, bases, or most organic solvents.

The resistance of a filter material to degradation when in contact with a specific chemical or solvent. Always verify compatibility between membrane material, housing, and the solution being filtered before use.

A separation technique that partitions components in a mixture between a stationary phase and a mobile phase based on differential affinities. Common types include affinity, ion exchange, size exclusion, and hydrophobic interaction chromatography.

A filtration process aimed at removing particulates or turbidity from a solution while retaining the liquid product in the filtrate. The opposite of solids recovery.

A substance consisting of microscopically dispersed particles (1–1,000 nm) suspended in a continuous medium. Colloids are too large to pass through ultrafiltration membranes but may pass through microfiltration membranes.

A filtration mode in which the feed flow is directed perpendicularly through the membrane. Retained particles accumulate on the membrane surface, eventually limiting flow. Also called normal flow filtration (NFF).

A membrane-based process used to exchange the buffer of a solution or remove small molecules. Fresh solvent is continuously added as filtrate passes through the membrane, gradually diluting unwanted components.

The pressure difference across a filter membrane (inlet pressure minus outlet pressure). Also called transmembrane pressure (TMP). Monitoring differential pressure helps detect membrane fouling or clogging.

The series of purification steps following a bioreaction or fermentation, including clarification, filtration, and chromatographic separations, to isolate and purify the desired biological product.

The liquid that exits a filter or chromatography column. Depending on context, this may be the desired product (filtrate) or the waste stream.

The process of washing a retained substance off a chromatography resin or membrane using a specific buffer or solvent, releasing it for collection.

Chemical compounds that can be released from a filter material into a solution under stressed conditions (elevated temperature, aggressive solvents). Important consideration in pharmaceutical and food applications.

The layer of retained solids that accumulates on the upstream surface of a membrane during filtration. Also called retentate or filter mat. In solids recovery applications, this is the desired product.

The liquid that passes through a filter membrane. In clarification processes, the filtrate is the desired product — the clarified solution from which particles have been removed.

The volume of liquid passing through a filter per unit of time, typically expressed in mL/min or L/hr. Influenced by applied pressure, membrane pore size, filter area, fluid viscosity, and particle load.

The volumetric flow rate of liquid per unit membrane area per unit time (e.g., L/m²/hr). A normalized measure of membrane throughput used to compare performance across different membrane sizes.

The accumulation of retained materials on or within a membrane, causing a reduction in flux and increased transmembrane pressure over time. Can be reversible (removable by cleaning) or irreversible.

A depth filter medium made from borosilicate glass fibers. Used for pre-filtration of high-particulate samples due to high dirt-holding capacity and excellent flow rates. Not suitable as a sterilizing barrier.

A regulatory framework ensuring products are consistently produced and controlled to quality standards. Filtration materials used in GMP environments must meet strict documentation, traceability, and extractables requirements.

High-Efficiency Particulate Air filter. Capable of capturing at least 99.97% of particles ≥ 0.3 µm from air. Used in cleanrooms, biosafety cabinets, and laminar flow hoods to maintain sterile environments.

A filtration format in which the membrane is formed into thin tubes (fibers). Feed flows through the interior lumen; permeate passes through the fiber wall. Used in tangential flow filtration for large-scale concentration and diafiltration.

Water-attracting. Hydrophilic membranes wet spontaneously with aqueous solutions and are preferred for filtering biological fluids, buffers, and water-based samples. Examples: PES, CA, PVDF (hydrophilic variant), Nylon.

Water-repelling. Hydrophobic membranes resist wetting by aqueous solutions and are preferred for filtering organic solvents, gases, and aggressive chemicals. Examples: PTFE, polypropylene (PP). Can be pre-wetted with alcohol for aqueous use.

A non-destructive test used to verify that a filter membrane is intact and free of defects before or after filtration. Common methods include the bubble point test, diffusion test, and pressure hold test.

A separation technique that separates charged molecules based on their affinity for a charged stationary phase. Positively charged resins (anion exchangers) bind negatively charged molecules and vice versa.

Chemical compounds that migrate from a filter or container material into a solution under normal use conditions. Unlike extractables (stressed conditions), leachables are measured under standard operating conditions and are critical for drug product safety.

A measure of a filter's ability to remove microorganisms, expressed as log₁₀ of the ratio of organisms in the feed to organisms in the filtrate. A sterilizing-grade filter typically achieves an LRV ≥ 7 for Brevundimonas diminuta.

A standardized threaded fitting used on syringe filters and syringes to create a secure, leak-free connection. More secure than slip Luer connections, especially for high-pressure applications.

A friction-fit syringe connection that simply pushes onto the syringe tip without threading. Easier to connect and disconnect than a Luer lock but less secure under elevated pressure.

Filtration of particles typically visible to the naked eye, generally larger than 10 µm. Used as a coarse clarification step or pre-filtration stage before finer filtration.

A thin, porous barrier that selectively allows certain substances to pass while retaining others. Membranes are characterized by their material, pore size, pore structure (symmetric vs. asymmetric), and surface chemistry.

Filtration of particles in the 0.1–10 µm range. Used to remove bacteria, suspended solids, and larger colloids. The most common laboratory filtration category, covering most syringe and membrane filter applications.

Material Safety Data Sheet / Safety Data Sheet. A document providing health, safety, and chemical compatibility information for a substance. Essential reference when verifying membrane compatibility with reagents and solvents.

A pressure-driven membrane process with pore sizes of 0.001–0.01 µm. Separates divalent ions, low-molecular-weight organics, and smaller viruses. Unlike ultrafiltration, nanofiltration separates particles based on both size and charge.

An approximate particle size at which a filter will retain a defined percentage (commonly 90–98%) of particles. Less precise than absolute rating; the nominal rating may vary depending on particle load and operating conditions.

A measure of the flow of water through a membrane normalized to pressure and temperature. Used as a baseline to detect membrane fouling or integrity loss during process operation.

A hydrophilic membrane material (polyamide) suitable for aqueous and polar organic solvents. Widely used in HPLC sample preparation and general laboratory filtration. High protein binding — avoid for biological samples where recovery is critical.

The concentration and volume of particles in the feed solution. High particle loads can rapidly foul a fine membrane; in these cases, a coarser pre-filter should be used upstream to extend the life of the final filter.

The fraction of a feed solution that passes through a membrane. Synonymous with filtrate. In ultrafiltration and TFF applications, the permeate contains small molecules and solvents while larger molecules are retained.

A hydrophilic, low-protein-binding membrane material widely used in biological filtration. Excellent choice for sterile filtration of cell culture media, buffers, and protein solutions. Avoid strong acids, ketones, and DMF.

A chemically resistant membrane material with very low extractables. Suitable for aggressive acids, bases, and oxidizing agents. Not compatible with aromatic or chlorinated solvents.

The diameter of the openings in a filter membrane, typically expressed in micrometers (µm). Pore size determines which particles are retained and which pass through; the correct choice depends on the target organism or molecule.

A coarser filter placed upstream of the final filter to remove large particles before they reach and clog the finer membrane. Significantly extends the service life of downstream filters in high-particulate applications.

The tendency of a membrane material to adsorb proteins from a solution, resulting in sample loss. Low-protein-binding materials (PES, CA, PVDF) are preferred for biological filtration where accurate sample recovery is critical.

A hydrophobic, chemically inert membrane material compatible with virtually all organic solvents, concentrated acids, and bases. Ideal for non-aqueous filtration and gas filtration. Requires pre-wetting with alcohol before use with aqueous solutions.

A membrane material available in both hydrophilic and hydrophobic variants. Low protein binding; compatible with aqueous solutions and mild organic solvents. The hydrophilic version is widely used for protein filtration and western blotting applications.

A hydrophilic, low-extractable membrane material compatible with aqueous solutions and mild organic solvents. Frequently used for HPLC sample preparation due to minimal interference with chromatographic analysis.

The fraction of the feed solution that is retained by the membrane and does not pass through as permeate. In concentration applications, the retentate contains the desired product at increased concentration.

A pressure-driven membrane process that removes dissolved salts, small molecules, and almost all impurities from water. The tightest common membrane process, with pore sizes below 0.001 µm. Used in water purification and desalination.

The removal of microorganisms from a liquid using a membrane with an absolute pore size of 0.2 µm or smaller. The standard method for sterilizing heat-sensitive solutions such as cell culture media, vaccines, and injectable drugs.

A small, disposable filter unit attached to the end of a syringe for fast, small-volume filtration (typically up to 100 mL). Available in a wide range of membrane materials, pore sizes, and housing diameters (4–30 mm).

A chromatographic method that separates molecules based on their size (hydrodynamic volume). Larger molecules elute first, as they cannot penetrate the pores of the stationary phase. Also called gel filtration.

A filtration mode in which the feed flows parallel (tangentially) to the membrane surface rather than directly through it. This cross-flow sweeps retained particles away from the membrane, reducing fouling and enabling continuous processing of large volumes.

A measure of how indirect the path of a pore is through a membrane. Higher tortuosity means particles must travel a more circuitous route, improving retention but also increasing resistance to flow.

The net driving pressure across a membrane, calculated as the average of the inlet and outlet pressures minus the permeate pressure. Monitoring TMP is critical in TFF processes to avoid membrane fouling and compaction.

A measure of the cloudiness or haziness of a liquid caused by suspended particles. Turbidity reduction is a common goal in clarification filtration and is measured in NTU (Nephelometric Turbidity Units).

Filtration of particles in the 0.001–0.1 µm range. Used to separate macromolecules, viruses, and proteins from smaller solutes. Commonly used for concentration, buffer exchange, and virus removal in biopharmaceutical manufacturing.

A biocompatibility standard set by the United States Pharmacopeia. Plastics and materials rated USP Class VI have passed a series of biological reactivity tests, confirming they are safe for contact with pharmaceutical products and body fluids.

A filtration method in which a vacuum is applied to the downstream side of a membrane to draw liquid through. Commonly used with membrane disc filters in Buchner funnels or filter holders for laboratory-scale clarification.

A measure of a fluid's resistance to flow. More viscous fluids require higher operating pressures to achieve the same flow rate through a membrane. High viscosity solutions may benefit from warming or dilution prior to filtration.

The total volume of liquid held within a filter or chromatography column, including the spaces between and within the packing material. Important for calculating sample dilution and recovery in column-based separations.

The ability of a liquid to spread across and penetrate a membrane surface. Hydrophilic membranes are readily wetted by water; hydrophobic membranes resist wetting by aqueous solutions and must be pre-wetted with a wetting agent such as isopropanol.

A substance, typically a lower-surface-tension solvent like isopropanol or methanol, used to pre-wet a hydrophobic membrane before introducing aqueous solutions. This allows water to flow through the membrane by initially reducing surface tension.