 |
To quickly find a word on a web page:
- Press "Ctrl" and "F" on your keyboard.
- Type in the word you search for.
- Push "Find next"
A
| Additive |
| A substance added to another in relatively small amounts to effect a desired change in properties. |
| Adsorption |
| The binding of molecules to a surface as a result of a chemical or physio-electric interaction between the membrane surface or the chromatographic resin and the molecule. |
| Affinity chromatography |
| A technique in which a biospecific adsorbent is prepared by coupling a specific ligand (such as an protein, peptide or nickel) for the molecule of interest to a solid support. This immobilized ligand will interact only with molecules that can selectively bind to it. Molecules that will not bind elute unretained. The retained compound can later be released in a purified state. |
| Agarose |
| High-molecular-weight polysaccharide used as a separation medium in bead form for biochromatography. |
| Air diffusion rate |
| The rate at which air diffuses through the wetted pores of membrane at a given differential pressure. Measuring the air diffusion rate is a method used to check the integrity of a membrane filter. |
| Anion exchange chromatography |
| The ion exchange procedure used for the separation of anions. The tetra-alkyl-ammonium group is a typical strong anion exchange functional group. |
| Asymmetric membrane |
| A membrane that is made such that the pore size increases through the membrane matrix. |
| Asymmetry or Asymmetry factor |
| Factor describing the shape of a chromatographic peak. Theory assumes a Gaussian shape and that peaks are symmetrical. The peak asymmetry factor is the ratio (at 10% of the peak height) of the distance between the peak apex and the backside of the chromatographic curve to the distance between the peak apex and the front side of the chromatographic curve. A value > 1 is a tailing peak, while a value < 1 is a fronting peak. |
| Autoclave, autoclavability |
| An autoclave is a device that uses saturated steam at a specified pressure over time to kill microorganisms and thus achieve sanitization or sterilization. Because many materials change properties when exposed to moisture, heat, and pressure, products destined for this process must be specially engineered for autoclavability. |
Return to top
B
| Back flushing, backwash |
| Backflushing is used to elute strongly held compounds at the head of the column by reversing the flow direction of the mobile phase through a chromatographic column. In case of membranes reversing the permeate flow can mechanically clean the. |
| Baseline |
| The more or less constant signal observed when only the mobile phase passes through the detector. This steady baseline portion of the chromatogram is the reference from which quantitative measurements can be made. |
| Bed volume |
V = (π x r2) x h where
r = inner radius of the column tube
h = the height of the column tube |
| Beta ratio |
A standard method of rating a filter's ability to remove particles. Beta (x) = # particles > size (x) upstream / # particles > size (x) downstream where
x = particle size in microns |
| Binding |
| The process by which some components in a feed solution adhere to the membrane. Binding can be desirable in some instances, but often, as in the case of protein binding during sterile filtration can result in a loss of valuable product. |
| Binding capacity |
| The binding capacity describes the actual amount of a sample that will bind to the medium packed in a column under defined conditions. It is determined by saturating a gel with sample and then measuring the amount of sample that binds. Parameters like pH, ionic strength, the counter-ion and the sample all influence the available capacity. Available capacity will change depending on the experimental conditions. It is essential to take these conditions into consideration when comparing the available capacities of different chromatography media. |
| BioProcess™ system |
| An automated liquid chromatography system used from process scale, up through clinical trials to full-scale production. |
| Biosafety test |
| A class of tests that determine whether a chromatographic media or filter's material of construction can induce systemic toxicity, skin irritation, sensitization reaction, or other biological responses. These test are often completed by labs in vivo or in vitro. For example, United States Pharmacopoeia Class VI Plastics Test involves both the implantation and extraction of drug product contact surfaces to demonstrate that these materials are not toxic to various mammalian cells. |
| Blinded |
| When a filter is blinded, it means that particles have filled the pores and the flow through the filter from the feed side to the permeate side is reduced or stopped. |
| Bubble point |
| The minimum pressure required to overcome the capillary forces and surface tension of a liquid in a fully wetted membrane filter. The bubble point value is determined by observing when bubbles first begin to emerge on the permeate side or downstream side of a fully wetted membrane filter when pressurized with a gas on the feed (upstream) side of the membrane filter. |
| Bubble point test |
| The test procedure for determining the bubble point of the largest pores in a microfiltration membrane. |
| Buffer |
| A mixture of an acid and its conjugate base; its pH changes slowly upon the addition of small amounts of acid or base. |
| Buffer exchange |
| Filtration process used for the removal of smaller ionic solutes, whereby the feed solution is washed, usually repeatedly, and one buffer is removed and replaced with an alternative buffer. |
Return to top
C
| Capacity |
| see: Binding capacity and Dynamic binding capacity |
| Capture step |
| The initial purification of the target molecule from crude or clarified source material. The objectives are the rapid isolation, stabilization and concentration of the desired molecule. |
| Cartridge or cartridge filter |
| A filtration or separation device having a membrane encapsulated within a housing. The housing normally has feed and permeate ports and in the case of cross flow filters, a retentate port. All of these ports may be used to control the flow parameters of fluid into and out of the housing and through the membrane. |
| Cartridge pressure drop |
| The differential pressure between cartridge inlet and outlet. |
| Cassette |
| A device used for cross flow filtration, typically in a rectangular form comprised of stacked flat sheets of membrane integrally bonded together. Most cassettes are typically designed to fit into a standard cassette holder where the feed, permeate and any retentate ports mate with appropriate fittings on the cassette holders. |
| Cation exchange chromatography |
| The form of ion exchange chromatography that uses resins or packings with functional groups that can separate cations. A sulphonic acid would be an example of a strong cation exchange group; a carboxylic acid would be a weak cation exchange group. |
| Cell harvesting |
| The process of concentrating (dewatering) the cell mass after fermentation. Cell slurries in excess of 70% wet cell weight are achievable. The cells may also be washed to prepare them for further processing, such as freezing or lysing. Unlike clarification processing, with cell harvesting, the cells are the target material. |
| cGMP |
| The minimum requirements by law for the manufacture, processing, packaging, holding or distribution of a material as established in Title 21 of the Code of Federal Regulations. Examples are Part 211 for Finished Pharmaceuticals, Part 606 for Blood and Blood Components, Part 820 for Medical Devices and Quality System Regulations (QCR). |
| Channel height |
| The height of the path that the feed/retentate solution must pass through for a flat membrane cassette. |
| Channel length |
| The total length that the feed solution must travel along a flat cassette to reach the retentate outlet. |
| Chemical compatibility or resistance |
| The ability of the components of a packed column or a filter to resist chemicals that can influence it's performance. For example, some chemicals could cause the filter to shed particles, swell, or dissolve filter components. Repeatable performance requires that filters are resistant to all the chemicals that they are exposed to at a given concentration, temperature, and total exposure time. |
| Chromatogram |
| A plot of detector signal output versus time, elution volume or column volume during the chromatographic process. |
| Chromatographic column |
| Vessel, typically in cylindrical shape including attached accessory parts like valves, for harboring the chromatography medium. |
| Cleaning frequency |
| The number of chromatographic runs, after a cleaning cycle has to occur. |
| Cleaning in place (CIP) |
| The process of cleaning a chromatography or filtration device without removing it from its system. |
| Clogging |
| The process in which solids block the filter or the chromatographic column with increasing |
| Column back pressure |
| The pressure of a chromatography system is measured right after the system pump. This pressure is called system back pressure. The additional pressure if a column is attached to the system is called column back pressure. |
| Column dead volume |
| (Vd). The volume outside of the column packing itself. The interstitial volume (intra-particle volume + inter-particle volume) plus extra column volume (contributed by injector, detector, connecting tubing, and end-fittings) all combine to create the dead volume. This volume can be determined by injecting an inert compound (i.e. a compound that does not interact with the column packing). Also abbreviated V0 or Vm. |
| Column equilibration |
| To achieve a stable and equal distribution of a desired buffer, a column packed with a chromatography medium has to be run in the respective buffer to a point where pH, conductivity and UV, measured at the column outlet, are identical to the respective values of the applied buffer. |
| Column performance |
| The performance of a column can be determined by checking the HETP and the asymmetry factor. |
| Composite membrane |
| A membrane that is made up of two or more layers that are usually chemically or structurally different. |
| Concentrate |
| Also called retentate. The part of the process solution that does not pass through a cross flow membrane filter. |
| Concentration |
| Cross flow filtration process in which the components that do not pass through the membrane remain in the feed loop and increase in concentration. |
| Concentration factor |
| The concentration factor equals the ratio of the initial feed volume to retentate volume after separation. For example, if the initial flow volume is 1000 ml and the final retentate volume is 10 ml, the concentration factor is 10-times. |
| Concentration polarization |
| The build-up of molecules of dissolved substances (solutes) on the surface of the membrane filter during filtration. The concentration polarization layer increases resistance to filtrate flow and reduces the permeate flux, thus decreasing filtration efficiency. |
| Concurrent process validation |
| Establishing documented evidence that a process does what it purports to do based on information generated during actual implementation of the process. |
| Conductivity |
| Measurement of a substances ability to conduct an electric current. Measured in Siemens/cm. See also ionic strength. |
| Counterion |
| In an ion-exchange process, the ion in solution used to displace the ion of interest from the ionic site. In ion pairing, it is the ion of opposite charge added to the mobile phase to form a neutral ion pair in solution. |
| Cross-linking |
| During the process of co-polymerization of resins to form a three dimensional matrix, a difunctional monomer is added to form cross-linkages between adjacent polymer chains. The degree of cross-linking is determined by the amount of this monomer added to the reaction. For example, divinylbenzene is a typical cross-linking agent for polystyrene ion-exchange resins. The swelling and diffusion characteristics of a resin are governed by its degree of cross-linking. |
| Cross flow filtration |
| Also called tangential flow filtration. In cross flow filtration (CFF), the feed solution flows parallel to the surface of the membrane. Driven by pressure, some of the feed solution passes through the membrane filter. Most of the solution is circulated back to the feed tank. The movement of the feed solution across the membrane surface helps to remove the buildup of foulants on the surface. |
| Cross flow rate |
| Also called retentate flow rate. The flow rate of solution that remains in the feed loop as measured in the retentate line. |
| Cutoff |
| Nominally, the smallest entity that will pass through a separations device to become permeate (filtrate) larger particles (where retention is >90%) are thus "cut off" from the permeate. Actual cutoff values of any given device or lot of devices usually must be determined empirically. See also: Molecular weight cut off (MWCO) and Nominal molecular weight cutoff (NMWC). |
Return to top
D
| Darcy's law |
In 1856, a French hydraulic engineer named Henry Darcy published an equation for flow through a porous medium that today bears his name. Q = KA (h1-h2)/L where
Q = volumetric flow rate (m3/s or ft3/s)
A = flow area perpendicular to L (m2 or ft2)
K = hydraulic conductivity (m/s or ft/s)
L = flow path length (m or ft)
h = hydraulic head (m or ft)
h1-h2 = denotes the change in h over the path L. |
| Dead-ended filtration |
| Also called normal flow filtration. In dead-ended filtration, liquid flows perpendicular to the filtration media, and all of the feed passes through. |
| Degassing |
| The process of removing dissolved gas from the mobile phase before or during use. Dissolved gas may come out of solution in the detector cell and cause baseline spikes and noise. Dissolved air can affect electrochemical detectors (by reaction) or fluorescence detectors (by quenching). Degassing is carried out by heating the solvent or by vacuum (in a vacuum flask), or on-line using evacuation of a tube made from a gas-permeable substance such as PTFE, or by helium sparging. |
| Depth filter |
| A thick filter that captures contaminants within its structure. A membrane filter primarily captures contaminates on its surface. |
| Depyrogenate |
| The removal of pyrogens (lipopolysaccharides) from a process solution. |
| Desalting |
| Technique in which low-molecular-weight salts and other compounds are removed from non-ionic and high-molecular-weight compounds. An example is the use of a reversed-phase packing to retain sample compounds by hydrophobic effects but to allow salts to pass through non-retained. Use of a SEC column to exclude large molecules and retain lower-molecular-weight salts is another example. See also diafiltration. |
| Desorption |
| The opposite of adsorption i.e. from the ion exchanger essentially two possibilities exist to desorb sample molecules: reducing the net charge by changing pH or adding a competing ion to "block" the charges on the ion exchanger. |
| Diafiltration |
| Diafiltration is a unit operation that incorporates ultrafiltration membranes to remove salts or other microsolutes from a solution. Small molecules are separated from a solution while retaining larger molecules in the retentate. Microsolutes are generally so easily washed through the membrane that for a fully permeated species about 3 volumes of diafiltration water will eliminate 95% of the microsolute. |
| Dialysis |
| Removal of small molecules from a solution of macromolecules by allowing them to diffuse through a semi-permeable membrane into water or a buffer solution. This osmotic pressure separations method is controlled by the concentration gradient of salts across the membrane. |
| Differential pressure |
| In cross flow filtration the pressure drop along the cartridge between the feed (inlet) port and the retentate (outlet) port. |
| Diffusion |
| Movement of gas molecules caused by a concentration gradient. |
| Direct flow filtration |
| Filtration process where the entire feed stream flows through the filter's media. Also reffered to as normal flow filtration and dead-end filtration. |
| Downstream processing |
| Starting with a feed stream free of cells and cell debris, the purification sequences involving chromatography and membrane separations to achieve final product purity. |
| Drain valve |
| Valve for draining off material in a filter housing usually at the lowest point. |
| Drug master file |
| A submission to FDA that can be used to provide detailed information about facilities, or articles used in the manufacturing, processing, packaging, and storing of one or more human drugs. |
| Dynamic binding capacity |
| Dynamic capacity describes the amount of sample which will bind to a gel packed in a column run under defined conditions. The dynamic capacity for any media is highly dependent on running conditions, sample preparation and even origin of the sample. In general the lower the flow rates, the higher the dynamic capacity. As the flow rate approaches zero, the dynamic capacity approaches the available capacity. Dynamic binding capacities are determined by loading a sample containing a known concentration of the target molecule, and monitoring for the molecule in the column flow-through while applying sample. |
Return to top
E
| Effective area |
| In a membrane separations device, the active area of the membrane exposed to flow. |
| Efficiency |
| Description of the peak width and shape. The efficiency of a column is usually expressed as a plate number and an asymmetry factor. |
| Effluent |
| The stream of fluid leaving the filter. |
| Eluate |
| Combination of mobile phase and solute exiting column, also called effluent. |
| Endotoxin |
| The outer cell wall of gram-negative bacteria. |
| EtO, Ethylene oxide sterilization |
| A sterilization process still common for biomedical products, in which product is subjected to steam and highly toxic ethylene oxide gas. Because many materials change properties when exposed to moisture and EtO byproducts, products destined for this process must be specially engineered for EtO sterilization. |
| Exclusion limit |
| In SEC, the upper limit of molecular weight (or size), beyond which molecules will elute at the same retention volume, called the exclusion volume. Many SEC packings are referred to by their exclusion limit. |
| Exclusion volume |
| (Ve). The retention volume of a molecule on a SEC packing; all molecules larger than the size of the largest pore are totally excluded and elute at the interstitial volume of the column. |
| Expanded bed adsorption (EBA) mode |
| Expanded bed mode is a single pass operation in which desired proteins are purified from crude, containing feed-stock containing particles without the need for separate clarification, concentration and initial purification. The expansion of the adsorbent bed creates a distance between the adsorbent particles, i.e. increased voidage (void volume fraction) in the bed, which allows for unhindered passage of cells, cell debris and other particles during application of crude feed to the column. |
| Extractables |
| Substances that may dissolve or leach from a membrane during filtration and contaminate the process solution. For example, the leachates might include wetting agents in the membrane, membrane-cleaning solutions, or substances from the materials used to encase the membrane. |
Return to top
F
| Feed |
| Material or solution that you apply on chromatography column or introduce into a membrane separation system device. |
| Feed pressure |
| The pressure measured at the feed port of a separation device such as a chromatographic column, a cartridge or cassette . |
| Feed stream flow rate |
| Volumetric flow rate of the feed. Measured in volume per unit time. |
| Fiber |
| More correctly called hollow fiber membrane. |
| Filter area |
| The surface area of filter media inside a separation device. |
| Filter efficiency |
| Filter efficiency represents the percentage of particles that are removed from the fluid by the filter. |
| Filtrate |
| Also called permeate. The portion of the process fluid that passes through the membrane. |
| Filtrate flow rate |
| The instantaneous volume per unit time of filtrate produced by a system, typically measured on a filtrate flow meter. |
| Filtration |
| Removal of particles, normally solids, from a fluid. These can be contaminants or valuable products. |
| Filtration efficiency |
| A filter's ability to remove particles of the specified size, expressed as a percentage or as a Beta Ratio. |
| Flow rate |
| The volumetric or linear rate of flow of mobile phase through a chromatography column. |
| Flowpath length, nominal flowpath length |
| The total length that a feed solution travels from inlet to outlet. Flowpath length is an important parameter to consider when doing any process development, system design, or scale-up or scale-down experiments. The flow path length and other fluid channel geometries such as lumen diameter or channel height can impact the fluid dynamics of the system and will directly impact pump requirements and differential pressure of the filtration step. |
| Flux |
| Flux represents the volume of solution flowing through a given membrane area during a given time. Expressed as LMH (liters per square meter per hour). |
| Flux rate in LMH |
| Flux rate in LMH = {permeate flow (ml/min) ÷ cassette surface area (m2)} × 0.06 |
| Fouling |
| Accumulation of material on the surface of the chromatography media or on the membrane that can slow and alter the process. |
| Fractionation |
| Separation of molecules in a solution based on differences in the properties of the molecules. |
| Frit |
| The porous element at either end of a column that serves to contain the column packing. It is placed at the very ends of the column tube or, more commonly, in the end-fitting. Frits are made from stainless steel or other inert metal or plastic, such as porous PTFE or polypropylene. |
Return to top
G
| Gamma sterilization |
| A type of sterilization process accomplished by bombarding the object to be sterilized with electron beam, x-ray, or 60Co or 137Cs irradiators. All generate forms of gamma rays, radiant energy at short wavelength (0.1 nm or less). The governing standard is ISO 11137 -Sterilization of Healthcare Products- Requirements for Validation and Routine Control -Radiation Sterilization. Because some product materials can be adversely affected by gamma radiation, objects destined for gamma sterilization must be engineered specifically for this process. |
| Gel filtration chromatography (GFC) |
| Size-exclusion chromatography (SEC) carried out with aqueous mobile phases. |
| Gel layer |
| During the filtration process, the thin layer of particles or molecules that may build up at the membrane surface. It is also referred to as the concentration polarization layer. High trans membrane pressure can lead to an increase in the thickness of the gel layer and negatively impact the filtration process by reducing flux and inhibiting passage though the membrane. |
| GLP |
| Good laboratory practice, regulations issued by the FDA describing practices for conducting non-clinical laboratory studies. |
| Gradient elution |
| Technique for the separation of molecules by increasing mobile phase strength (i.e. conductivity etc.) over time during the chromatographic separation. Gradients can be continuous or stepwise. |
Return to top
H
| HETP |
Height equivalent to a theoretical plate. A carryover from distillation theory: a measure of a column's efficiency. For a typical HPLC column well-packed with 5 µm particles, HETP (or H) values are usually between 0.01 and 0.03 mm.HETP = L/Nwhere
L = column length
N = the number of theoretical plates |
| High performance liquid chromatography (HPLC) |
| A separation technique that uses small particle size, narrow bore columns, and high inlet pressures to achieve separation in short periods of time with high resolution. Any form of column chromatography which uses a liquid mobile phase can be extended to HPLC. |
| Hold-up volume |
| Quantity of fluid remaining within the filtration media after draining the system. |
| Hollow fiber |
| The tube-like structure made from a membrane and sealed inside a cross flow cartridge.When in use, the feed stream flows into the inner diameter of one end of the hollow fiber and the retentate (the material that does not permeate through the walls of the hollow fiber) flows out the other end. The material that passes through the membrane (walls of the hollow fiber) is called the permeate. |
| Housing |
| The mechanical structure that surrounds and supports the membrane or filter element. The housing normally has feed, retentate, and permeate ports that direct the flow of process fluids into and out of the filter assembly. |
| Hydrophilic |
| "Water-loving": refers both to stationary phases that are compatible with water and to water soluble molecules in general. Most chromatography media used to separate proteins are hydrophilic in nature and should not sorb or denature protein in the aqueous environment. |
| Hydrophobic |
| "Water-hating": refers both to stationary phases that are not compatible with water and to molecules in general that have little affinity for water. Hydrophobic molecules have few polar functional groups: most are hydrocarbons or have high hydrocarbon content. |
| Hydrophobic interaction chromatography (HIC) |
| A technique in which reversed-phase packings are used to separate molecules by virtue of the interactions between their hydrophobic moieties and the hydrophobic sites on the surface. High salt concentrations are used in the mobile phase; separations are effected by changing the salt concentration. The technique is analogous to salting out molecules from solution. Gradients are run by decreasing the salt concentration over time. |
Return to top
I
| Impurity |
| Impurities are intrinsic unwanted compounds of a respective sample. |
| In vitro |
| An experiment performed in a test tube, Petri dish, or other lab apparatus with parts of a living organism, such as testing a drug with tissue samples. From Latin, meaning "in glass". |
| In vivo |
| An experiment performed using a living organism. From Latin, meaning "in live [subjects]". |
| Inlet |
| The initial part of the column or a filtration device, where the solvent and sample enter. In case of a chromatographic column there is usually an inlet frit that holds the packing in place and, in some cases, protects the packed bed. |
| Inlet pressure |
| The pressure driving a fluid into the feed port of a separation device. |
| Installation qualification (IQ) |
| The Installation Qualification provides a systematic method to check the system/equipment static attributes prior to normal operation. A detailed description of the system should be included as a part of IQ. This description includes all important major/minor components of the system. The availability of the applicable SOPs must be verified. These include system/equipment operation, maintenance, cleaning and/or sanitization. |
| Intermediate purification step |
| Further removal of bulk impurities with the main objectives on concentration and purification. |
| Ion-exchange chromatography (IEC) |
| A mode of chromatography in which ionic substances are separated on cationic or anionic sites of the packing. The sample ion (and usually a counterion) will exchange with ions already on the ionogenic group of the packing. Retention is based on the affinity of different ions for the site and on a number of other solution parameters (pH, ionic strength, counterion type, etc.). |
| Ionic Strength |
| The weight concentration of ions in solution, computed by multiplying the concentration of each ion in solution (C) by the corresponding square of the charge on the ion (Z) summing this product for all ions in solution and dividing by 2. |
| Isocratic elution |
| Use of a constant-composition mobile phase in liquid chromatography. |
| Isoelectric point |
| The Isoelectric point is the pH of a solution or dispersion at which the net charge on the macromolecules or colloidal particles is zero. |
Return to top
L
| Leakage |
| Leakage occurs when resin derived substance (ligands or other compounds) disintegrate from the matrix. |
| Linear velocity |
| The velocity of the mobile phase moving through the column, expressed in cm/h. Related to flow rate by the cross-sectional area of the column. |
| Lumen |
| The inner open space or cavity of a single hollow fiber element that is used in the construction of hollow fiber cartridges. |
Return to top
M
| Macrovoid |
| A generally undesirable open space in a membrane filter that is appreciably larger than the average of the pore openings in a given filter. Macrovoids can lead to pinhole defects resulting in unwanted passage that directly impacts final product yield. Macrovoids can also impact the overall membrane strength and thus the device's ability to maintain integrity under pressure. |
| Maximum operating pressure |
| The maximum pressure allowed in a device or system. |
| Media exchange |
| A filtration step used to exchange one type of media for an alternative type of media during an aseptic cell culture separation. |
| Media migration |
| Media migration occurs when solid components of a filter (particles, adhesives, etc.) break free of the filter and enter the process solution. |
| Medium (media) |
| The component of a separation device. For example, the chromatographic matrix in a chromatography column or the membrane in a membrane cassette. |
| Membrane |
| A thin layer of a highly engineered material with pores used to separate particles, biological matter, and molecules from a solution. |
| Membrane recovery |
| The degree to which the original performance of a membrane can be restored by cleaning. |
| Membrane test |
| A process, based on membrane bubble point characteristics, for testing the integrity of the membranes. |
| Microfiltration |
| The process of removing particles from a liquid by passing it through a porous membrane under pressure. Microfiltration usually refers to removing submicron-size particles. |
| Micron (micrometer, µm) |
| One one-millionth of one meter. |
| Microporous membrane |
| A thin, porous film or hollow fiber having pores ranging from 0.01 to 10 µm. Science and industry use microporous membranes to separate suspended matter from liquids. |
| Mobile phase |
| The solvent that moves the solute through the column. |
| Molecular weight cut off (MWCO) |
| The size designation in Daltons for ultrafiltration membranes. The molecular weight of the globular protein that is 90% retained by the membrane. No industry standard exists, hence the MWCO ratings of different manufacturers are not always comparable. |
Return to top
N
| Nanofiltration |
| Separation processes targeted for solutes having molecular weights from 500Da to 1000Da |
| Nominal filter rating |
| A rating that indicates the percentage of particles of a specific size or molecules of a specific molecular weight that will be removed by a filter. No industry standard exists; hence the ratings from manufacturer to manufacturer are not always comparable. |
| Nominal molecular weight cutoff |
| In ultrafiltration, the molecular weight size of a protein or other solute (in thousands of Daltons) that will be retained to 90% by the membrane. |
| Normal flow filtration |
| Also called dead-ended filtration. In normal flow filtration, liquid flows perpendicular to the filter media, and all of the feed passes through. |
| Normalized water permeability (NWP) |
| The water flux rate at 20°C. Flux (normalized to 20°C) = Cassette flux measured temp. (°C) × 20°C ÷ measured temperature (°C) |
Return to top
O
| Oleophobic |
| Membranes that repel nonpolar fluids such as oil and lubricants. |
| Operation qualification (OQ) |
| The documented evidence that the system or equipment performs as intended throughout all anticipated operating ranges. The Operational Qualification protocol contains the procedures to verify specific dynamic attributes of a system or equipment throughout its operating range, which may include worst case conditions. Applicable Standard Operating Procedures and training procedures are documented in the appropriate protocol section. The executed operational qualification protocol verifies that the system or equipment performs as intended. |
| Overload |
| In preparative chromatography, the overload condition is defined as the mass of sample injected onto the column at which efficiency and resolution begin to be affected if the sample size is further increased. |
Return to top
P
| Packed bed mode |
| A traditional chromatography mode, where the resin is confined between the bottom of the column and the flow adapter. |
| Particle size distribution |
| The distribution of particle sizes (number or weight fraction) in a fluid. |
| Peak shape |
| Describes the profile of a chromatographic peak. Theory assumes a Gaussian peak shape (perfectly symmetrical); peak asymmetry factor describes shape as a ratio. |
| Performance Qualification (PQ) |
| The documented evidence that the system, equipment or process is capable of consistently producing a safe product of high quality. The Performance Qualification protocol describes the procedures that verify the specific capabilities of a process equipment/system through the use of simulation material and/or actual product. |
| Permeate |
| Also called filtrate. The portion of a process fluid that passes through a membrane. |
| Plate number |
| Refers to theoretical plates in a packed column. |
| PLC |
| Programmable logic controller, a purpose-made device for industrial control. Microprocessors, now common in desktop computers, were originally devised in the 1970s for PLCs or for the types of operations common to PLCs (polling or checking sensors and activating/de-activating valves and switches compared against programmed pre-sets or default levels). |
| Pleating |
| Folding filter media to increase the surface area that can be fitted into a given separation device |
| Point of break through |
| The breakthrough volume is useful in determining the total sample capacity of the column for a particular solute. |
| Polishing step |
| Final removal of trace impurities to gain high level purity of end product. |
| Pore |
| Small interconnecting passage through the membrane. The size and irregular path of a pore determines the removal rating of a membrane. |
| Pore size distribution |
| The range of pore sizes in a membrane. The tighter the pore size distribution, the better control one has over the filtration process. |
| Porosity |
| A measurement of the open space in a membrane. Also called open area or voids volume. |
| Pre-filtration |
| Removal of coarse particles/contaminants prior to final normally finer filtration. |
| Pre-treatment |
| The chemical or physical cleaning of a fluid prior to filtration or chromatography. |
| Pressure |
| An increase in the force exerted on something above standard atmospheric conditions, measured as gauge pressure (psig, barg). |
| Pressure-flow rate curve |
| To determine the optimal packing flow rate and pressure, a pressure versus flow rate curve for each lot of chromatography media is performed. |
| Pressure drop |
| The difference in pressure between two points. |
| Pressure, absolute |
| Gauge pressure plus 14.7 psi (1 bar). |
| Process scale chromatography |
| The chromatographic procedure and equipment used in industrial production are referred to process scale. |
| Process validation |
| Establishing documented evidence which provides a high degree of assurance that a specific process will consistently produce a product meeting its pre-determined specifications and quality attributes. |
| Prospective validation |
| Validation conducted prior to the distribution of either a new product, or product made under a revised manufacturing process, where the revisions may have affected the product's characteristics. It is also to ensure that the finished product meets all release requirements for functionality and safety. |
| Protein passage |
| The passage of protein into the permeate stream. |
| PSI |
| Pounds per square inch. A unit of pressure. 1 PSI = 6.78 kPa |
| Pyrogen |
| A substance (e.g. Endotoxin) that produces a fever within a warm-blooded animal when injected into the bloodstream. Filtration materials of construction that come in contact with injectable liquids must meet pyrogenicity standards. |
Return to top
Q
| Quality assurance |
| The activity of providing evidence that all the information necessary to determine that the product is fit for the intended use meets cGMP requirements. The quality assurance department executes this function. |
Return to top
R
| Re-equilibration |
| The equilibration phase after a chromatographic run. |
| Recirulation rate |
| Same as retentate flow rate |
| Recovery |
| The amount of solute (sample) that elutes from a chromatography column or can be collected in the retentate or permeate solution of a filtration device relative to the amount applied. |
| Regeneration |
| Returning the packing in the column to its initial state after gradient elution. Mobile phase is passed through the column stepwise or in a gradient. The stationary phase is solvated to its original condition. In ion-exchange chromatography, regeneration involves replacing ions taken up in the exchange process with the original ions that occupied the exchange sites. Regeneration can also refer to bringing back any column to its original state (e.g., the removal of impurities with a strong solvent). |
| Residence time |
| The time required for an incremental unit of feed solution to pass through a separations device. |
| Resolution (Rs) |
Ability of a chromatography media to separate chromatographic peaks. It is usually expressed in terms of the separation of two peaks. One attempts to achieve the best resolution possible. Resolution can be calculated as follows: Rs = 1.18 x (tR2 - tR1) / (wh1 + wh2) where
wh1 = peak width at half height (in units of time) of the first peak
wh2 = peak width at half height (in units of time) of the second peak
tR1 and tR2 refer to the retention times of the first respectively the second peak A value of 1 is considered to be the minimum for a measurable separation to occur and to allow good quantification. Values of 1.7 or larger are generally desirable for rugged methods. |
| Retentate |
| The portion of the feed solution that does not pass through a cross flow membrane filter. |
| Retention |
| The ability of a separation device to retain particles of a given size. |
| Retention time, adjusted Retention time |
The time between injection and the appearance of the peak maximum. The adjusted retention time t'R adjusts for the column void volume. t'R = tR - t0 where
tR = retention time
t0 (or tm) = retention time of unretained compound |
| Retention volume |
The volume of mobile phase required to elute a substance from the column. VR = Vm - KD Vs where
Vm = void volume
KD = distribution coefficient
Vs = stationary phase volume. |
| Retrospective validation |
| Validation of a process for a product already in distribution based upon establishing documented evidence. The review and analysis of historical manufacturing and product testing data that verifies a specific process can be consistently produced meeting its predetermined specifications and quality attributes. |
| Return flow |
| See: retentate |
| Reverse osmosis |
| Type of cross-flow filtration used for removal of very small solutes (<1,000 Daltons) and salts. It uses a semi-permeable membrane under high pressure to separate water from ionic materials. High pressure is necessary to overcome the natural osmotic pressure created by the concentration gradient across the membrane. |
| Reversed-phase chromatography (RPC) |
| The most common HPLC mode. Mobile phase is usually water and a water-miscible organic solvent such as methanol or acetonitrile. There are many variations of RPC in which various mobile phase additives are used to gain a different selectivity. |
| Robustness |
| The robustness of a procedure is a measure of its capacity to remain unaffected by small, but deliberate variations in method parameters and provides an indication of its reliability during normal usage. |
| Running buffer |
| The solution used to perform a chromatographic run. |
Return to top
S
| Sanitization |
| A cleaning process that destroys most living (pathogenic) microorganisms. |
| Sanitizing agent |
| An agent introduced into a system to kill organisms and prevent the growth of organisms. |
| Selectivity |
Same as separation factor or relative retention ratio. The separation factor is a measure of the time or distance between the maxima of two peaks. If a = 1, then the peaks have the same retention and co-elute. a = k2 / k1 where
k1 = retention factor of the first peak
k2 = retention factor of the second peak |
| Separation |
| During operation, the separation device divides a liquid or gas feed stream into separate components. |
| Shear rate |
A ratio of velocity and distance expressed in units of s-1. The shear rate for a hollow fiber cartridge is based on the flowrate through the fiber lumen and can be calculated as follows: g = 4q/πr3 where
g = shear rate, s-1
q = flow rate through the fiber lumen cm3s-1
r = fiber radius, cm |
| Sieving |
| Removal of particles from a feed stream as a result of entrapment within the depth of the membrane pore structure. |
| Size-exclusion-chromatography (SEC) |
| A chromatographic technique in which analytes are excluded from the stationary phase, and thus separated, based on their size. |
| Size-exclusion membrane separation |
| Mechanism for removing particles from a feed stream. Based strictly on the size of the particles versus the pore size that the feed stream is being filtered through. Retained particles are held back because they are larger than the pore opening. |
| Slurry |
| A thick mixture of adsorbent and solvent used to pour columns. Excess solvent is drained out as the adsorbent settles and more slurry is added until the column is filled. |
| Solute |
| An ionic or organic compound dissolved in a solvent, for example, the sugar in a cup of coffee is a solute. |
| Spiking |
| Adding a known amount of substance being measured to a sample in order to determine the original sample concentration by the known addition technique or to determine the accuracy of a direct measurement technique. |
| Starling flow |
| A portion of filtrate (permeate) that is driven back through the membrane in the reverse direction near the outlet of the cartridge, due to the high permeability of these membranes in the presence of permeate pressure. This phenomenon is most often associated with the operation of microfiltration membranes using permeate flow control. |
| Steam-in-place (SIP) |
| The process of sterilizing a tank or process device, such as a hollow fiber cartridge, with steam, without removing the device from the separation system. |
| Steam-in-place (SIP) |
| The process of sterilizing a separation device ?such as a hollow fiber cartridge? with steam without removing the device from the separation system. |
| Stepwise elution |
| Use of eluents of different compositions during the chromatographic run. These eluents are added in a stepwise manner. |
| Sterilization |
| A process that removes/destroys all (pathogenic) microorganisms from a solution or a solution processing system. |
| Surface area |
| In an adsorbent, refers to the total area of the solid surface as determined by an accepted measurement technique such as the BET method using nitrogen adsorption. |
| Surface filter |
| A filter in which particles larger that the pores are retained on the surface of the filter. |
| Swelling, Shrinking |
| Process in which a chromatographic resins increase or decrease their volume because of their solvent environment. Swelling is dependent upon the degree of cross-linking; low-cross-linking resins will swell and shrink more than highly cross-linked resins. If swelling occurs in a packed column blockage, increased back pressure can occur, and column efficiency can be affected. |
Return to top
T
| Tailing |
| The phenomenon in which the normal Gaussian peak has an asymmetry factor > 1. The peak will have skew in trailing edge. Tailing is caused by sites on the packing that have a stronger-than normal retention for the solute. |
| Tangential flow filtration |
| Also called cross flow filtration. In tangential flow filtration, the feed solution flows parallel to the surface of the membrane. Driven by pressure, some of the feed solution passes through the membrane filter. Most of the solution is circulated back to the feed tank. The movement of the feed solution across the face of the membrane surface helps to remove the buildup of foulants on the surface. |
| Theoretical plate (N) |
Column efficiency is expressed by the number of theoretical plates (N). The number of theoretical plates can be calculated using the equation below. Theoretical plates is a concept and a column does not contain anything resembling physical distillation plates or any other similar feature. Theoretical plates numbers are an indirect measure of peak width for a peak at a specific retention time. Columns with high plate numbers are considered to be more efficient (i.e., higher column efficiency) than columns with lower plate numbers. A column with a high number of plates will have a narrower peak at a given retention time than a column with a lower number of plates. Length of column relating to this concept is called height equivalent to a theoretical plate (HETP). N = 5.55 x (tR / w1/2)2
or
N = 16 x (tR / wb)2 where
tR = retention time
w1/2 and wb = width of the peak at half the peak height (hp/2) |
| Thermal stability |
| The ability of a membrane and filtering device to maintain its performance during and after exposure to elevated temperatures; for example, elevated temperature experienced during high-temperature processing or steam sterilization. |
| Throughput |
| (1) The volume of solution that will pass through a separations device before the filtrate output drops to an unacceptable level. (2) The rate at which a separations system will generate filtrate. |
| Titer reduction |
| The measurement of a filter's ability to remove microbes or virus from a fluid. |
| Transmembrane Pressure (TMP) |
| The force which drives liquid flow through a cross flow membrane. During filtration, the feed side of the membrane is under higher pressure than the permeate side. The pressure difference forces liquid through the membrane. TMP = {(feed pressure + retentate pressure) / 2} - permeate pressure |
| Tubule |
| Tube-like structure (larger ID fibers than hollow fibers) made from ultrafiltration or microfiltration membrane and sealed inside a cross flow cartridge. When in use, the feed stream flows into one end of the tubule and the retentate (the material that does not permeate through the walls of the tubule) flows out the other end. The material that does flow through the membrane (walls of the tubule) is called the permeate. |
| Turbidity |
| The measure of relative sample clarity of a liquid. Measurements are based on the amount of light transmitted in straight lines through a sample. The more light that is scattered by fine solids or colloids, the less clear (and more turbid) the solution. Often reported in NTU (nephelometric turbidity unit). |
Return to top
U
| Ultrafiltration |
| The separation of macrosolutes based on their molecular weight or size. |
| Upstream |
| The feed side of a separation process. |
| Upstream processing |
| Cellular separations including cell lysates, cell harvesting, clarification, and cell culture perfusion. |
Return to top
V
| Validation |
| Validation is establishing documented evidence which provides a high degree of assurance that a specific system (an interacting or interdependent group of items that function together to achieve a specific function), process, or facility will consistently produce a product meeting its predetermined specifications and quality attributes. Validation can be subdivided into three activities; installation, operational, and performance qualifications. |
| Validation change control |
| A formal monitoring system by which qualified representatives review proposed or actual changes that might affect validated status and take preventive or corrective action to ensure that the system retains its validated state of control. |
| Validation protocol |
| A validation protocol is a documented set of instructions designed to confirm specific static and/or dynamic attributes of the installation, operation or performance of a utility/system, equipment or process. |
| Viral clearance |
| The removal of viral contamination using specialized membranes or chromatography. In order to ensure that therapeutic drugs derived from certain sources are fully rid of any viral contamination, these protein solutions undergo viral clearance to inactivate or remove viral materials. |
| Viscosity |
| A measurement of a fluid's resistance to shear. A slow-flowing liquid such as gear oil has a higher viscosity than a free-flowing liquid such as mineral spirits. In a given separation process, higher-viscosity, Newtonian fluids have a lower flow rate through a cartridge than do lower-viscosity fluids. |
| Void time |
| The time for elution of an unretained peak (tm or t0) |
| Void volume (Vi) |
| The total volume of mobile phase in the column (the remainder of the column is taken up by packing material). It can be determined by injecting an unretained substance that measures void volume plus extra column volume. Also referred to as interstitial volume. Instead of Vi, V0 or Vm are sometimes used as symbols. For example, for non-rigid gels like Superose™, Sephacryl™ and other gel filtration gels, one can estimate the void volume of a column to be approximately 30% of the total bed volume. Also, the amount of open space within membrane filter media. |
| Volumetric flow rate |
| Units for measuring quantities of a substance by the volume they take up -usually at standard atmospheric (cubic feet, cubic meters). |
Return to top
W
| Wall effect |
| The consequence of the looser packing density near the walls of the rigid column. Mobile phase has a tendency to flow slightly faster near the wall because of the decreased permeability. The solute molecules that happen to be near the wall are carried along faster than the average of the solute band, and consequently, band spreading results. |
| Water flux |
| Measurement of the amount of water that flows through a cartridge. Clean water flux refers to the flux measurement made under standardized conditions on a new (and cleaned) membrane cartridge. (see also: flux) |
| Wetting |
| The process of filling pores of a hydrophobic membrane with water. Typical methods include use of alcohol as a wetting solution, or high pressure to drive air out. |
| Worst case |
| A set of conditions encompassing upper and lower processing limits and circumstances, including those within standard operating procedures, which pose the greatest chance of process or product failure, when compared to ideal conditions. Such conditions do not necessarily induce product or process failure. |
Return to top
Y
| Yield |
| The amount of target molecules that can be recovered from cross flow filtration and/or chromatography. Also called recovery. |
|
|
