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Filtration Resource Library
Filtration is done to achieve one of two things: to clarify and/or sterilize your filtrate, or to analyze the retentate left on the membrane. While there are several different applications that fall under either option, our products are designed to effectively support your entire filtration process and ensure that you achieve the most accurate results.
Laboratory filtration products come in many formats and with varying properties and yet the basics of filtration and many of the filter properties do not change. We have compiled these resources to help you select and use our products. Please contact our support services or your local sales representative for any further assistance you might require.
Filtration Basics
Please find a glossary of common filtration terms below. Note that device specifications are explained separately.
| Absorption | Separation of particles from a fuild based on their charge or affinity for a filtration media |
| Air Diffusion | The amount of gas, at a specified pressure, that is able to diffuse through a wetted membrane. Used for integrity testing. |
| Asymmetric | A membrane whose pore structure changes throughout its depth. |
| Binding | Membranes will all bind an amount of protein and other materials. |
| Bubble Point | The pressure required to push water or a water solution from the pores of a wetted membrane. Used for integrity testing. |
| Clarification | Filtration step or pore sizes targeted at rough removal of larger contaminants. Also used as a term for upstream filtration steps when there are multiple downstream filtration steps in a process. |
| Clogging (Plugging) | Term for a filter losing flow after retaining particles or microbes. |
| Differential Pressure | The difference in pressure across a filter. Calculated as the inlet pressure minus the outlet pressure. Used in determining how blocked or clogged a filter is. |
| Filtrate | The portion of flow that has passed through a membrane. |
| Flow Rate | The speed at which a fluid may pass a membrane. |
| Hydrophilic | A filter that readily accepts a liquid and wets easily. |
| Hydrophobic | A filter that does not readily wet and requires some pressure to process liquid. Hydrophobic filters are generally used to filter gases or vent containers. |
| Integrity | A membrane’s ability to function according to its specifications. |
| Integrity Testing | A test procedure geared towards verifying filter integrity and therefore performance or adherence to retention specifications. |
| Media | Generic term used for the substance performing the filtration such as the membrane. |
| Membrane | A type of filter generally made from a polymer resin cast into a thin sheet with a defined pore structure. |
| Microfiltration | A level of filtration widely considered to run from 0.05um to 100um in removal. This is the most common level of laboratory filtration. |
| Nanofiltration | A range of filtration considered to remove particles between 0.001um and 0.005um. Nanofiltration overlaps with Reverse Osmosis on the low range, and Ultrafiltration on the high range. |
| Permeate | The portion of flow that has passed through a membrane. |
| Plugging (Clogging) | Term for a filter losing flow after retaining particles or microbes. |
| Pore Size | The validated retention/removal cut off for a membrane. Note that a 0.22um membrane does not have 0.22um “holes” but rather a pore structure validated to remove all particles or microbes above its stated pore size. |
| Prefiltration | A filtration step specifically designed to reduce particle load prior to another, downstream filtration step. |
| Retentate | The particles, microbes or portion of flow that has been blocked from passing through the membrane |
| Retention | The ability for a membrane to retain particles or the related specification. |
| Reverse Osmosis | The greatest level of filtration used for removal of dissolved solids. De-salination of sea water, or removal of minerals from process water are examples. |
| Sterile Filtration | The removal of all microbes of concern for a product or application. Typically considered to be 0.2/0.22um, however, some industries such as wine or brewing consider larger pore sizes such as 0.45um to be sterile. |
| Surface Area | The amount of filter area. Effective surface area is the amount of usable filter area in a device. |
| Symmetric | A membrane whose pore structure is uniform throughout its depth |
| Tangential Flow | When a filter device operates so that all flow is not directed through the filtration media. There are two outlets. Flow is directed across the filter to allow for in process removal of retained particles. |
| Track-Etched Membrane | A membrane unlike others in that it has defined pores for surface removal rather than a sponge-like depth. Often used for microscopy. |
| Trans Membrane Pressure | Similar to differential pressure but often used when describing tangential flow filtration. |
| Ultrafiltration | A level of filtration that generally runs from 0.005um to 0.1um. Usually expressed in terms of molecular weight (MW) cut offs. Used for virus or endotoxin removal and protein separation. |
| Water Intrusion | The pressure required to wet a hydrophobic membrane |
Common Membrane Pore Sizes and Applications
0.65/0.8μm | 0.45μm | 0.2/0.22μm | 0.1μm |
Analysis of mold, fungi and yeast, clarification and prefiltration | Analysis of mold, fungi, yeast and some bacteria, sterility testing, clarification and prefiltration | Sterile filtration, sterility testing, final filtration
| Removal of mycoplasma |
Please find a glossary of common filtration terms below. Note that device specifications are explained separately.
| Absorption | Separation of particles from a fuild based on their charge or affinity for a filtration media |
| Air Diffusion | The amount of gas, at a specified pressure, that is able to diffuse through a wetted membrane. Used for integrity testing. |
| Asymmetric | A membrane whose pore structure changes throughout its depth. |
| Binding | Membranes will all bind an amount of protein and other materials. |
| Bubble Point | The pressure required to push water or a water solution from the pores of a wetted membrane. Used for integrity testing. |
| Clarification | Filtration step or pore sizes targeted at rough removal of larger contaminants. Also used as a term for upstream filtration steps when there are multiple downstream filtration steps in a process. |
| Clogging (Plugging) | Term for a filter losing flow after retaining particles or microbes. |
| Differential Pressure | The difference in pressure across a filter. Calculated as the inlet pressure minus the outlet pressure. Used in determining how blocked or clogged a filter is. |
| Filtrate | The portion of flow that has passed through a membrane. |
| Flow Rate | The speed at which a fluid may pass a membrane. |
| Hydrophilic | A filter that readily accepts a liquid and wets easily. |
| Hydrophobic | A filter that does not readily wet and requires some pressure to process liquid. Hydrophobic filters are generally used to filter gases or vent containers. |
| Integrity | A membrane’s ability to function according to its specifications. |
| Integrity Testing | A test procedure geared towards verifying filter integrity and therefore performance or adherence to retention specifications. |
| Media | Generic term used for the substance performing the filtration such as the membrane. |
| Membrane | A type of filter generally made from a polymer resin cast into a thin sheet with a defined pore structure. |
| Microfiltration | A level of filtration widely considered to run from 0.05um to 100um in removal. This is the most common level of laboratory filtration. |
| Nanofiltration | A range of filtration considered to remove particles between 0.001um and 0.005um. Nanofiltration overlaps with Reverse Osmosis on the low range, and Ultrafiltration on the high range. |
| Permeate | The portion of flow that has passed through a membrane. |
| Plugging (Clogging) | Term for a filter losing flow after retaining particles or microbes. |
| Pore Size | The validated retention/removal cut off for a membrane. Note that a 0.22um membrane does not have 0.22um “holes” but rather a pore structure validated to remove all particles or microbes above its stated pore size. |
| Prefiltration | A filtration step specifically designed to reduce particle load prior to another, downstream filtration step. |
| Retentate | The particles, microbes or portion of flow that has been blocked from passing through the membrane |
| Retention | The ability for a membrane to retain particles or the related specification. |
| Reverse Osmosis | The greatest level of filtration used for removal of dissolved solids. De-salination of sea water, or removal of minerals from process water are examples. |
| Sterile Filtration | The removal of all microbes of concern for a product or application. Typically considered to be 0.2/0.22um, however, some industries such as wine or brewing consider larger pore sizes such as 0.45um to be sterile. |
| Surface Area | The amount of filter area. Effective surface area is the amount of usable filter area in a device. |
| Symmetric | A membrane whose pore structure is uniform throughout its depth |
| Tangential Flow | When a filter device operates so that all flow is not directed through the filtration media. There are two outlets. Flow is directed across the filter to allow for in process removal of retained particles. |
| Track-Etched Membrane | A membrane unlike others in that it has defined pores for surface removal rather than a sponge-like depth. Often used for microscopy. |
| Trans Membrane Pressure | Similar to differential pressure but often used when describing tangential flow filtration. |
| Ultrafiltration | A level of filtration that generally runs from 0.005um to 0.1um. Usually expressed in terms of molecular weight (MW) cut offs. Used for virus or endotoxin removal and protein separation. |
| Water Intrusion | The pressure required to wet a hydrophobic membrane |
Common Membrane Pore Sizes and Applications
0.65/0.8μm | 0.45μm | 0.2/0.22μm | 0.1μm |
Analysis of mold, fungi and yeast, clarification and prefiltration | Analysis of mold, fungi, yeast and some bacteria, sterility testing, clarification and prefiltration | Sterile filtration, sterility testing, final filtration
| Removal of mycoplasma |
Membrane Information
Please find a glossary of common filtration terms below. Note that device specifications are explained separately.
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Please find a glossary of common filtration terms below. Note that device specifications are explained separately.
Please find a glossary of common filtration terms below. Note that device specifications are explained separately.
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Please find a glossary of common filtration terms below. Note that device specifications are explained separately.
device
Please find an explanation of common filter and filter device specifications below
| Membrane Flow Rate | The speed of fluid passing through a membrane. Pure water is typically used to develop specifications. Flow rate will vary by fluid and processing conditions. Note that device flow rate will be different from the membrane’s flow rate due to the device's effective surface area and properties. |
| Bubble Point (Water Intrusion) | The pressure at which a gas will pass through a wetted membrane. Specifications are typically developed based on pure water and/or a solution of IPA/water. Bubble point is used for integrity testing membranes. Water intrusion is a related term often used for the pressure at which water is pushed from hydrophobic membranes. |
| Component Toxicity | Plastic components are tested for toxicity per USP, FDA and other relevant guidelines. |
| Diffusion | The rate at which a gas will diffuse through a wetted membrane. Typically used for integrity testing of membranes and devices. |
| Endotoxin and Pyrogens | Bacterial endotoxins are typically tested to validate that filtration devices are non-pyrogenic or endotoxin free. |
| Extractables and Leechables | Polymer resins, both membranes and the polymers used in filtration devices, will have some degree of extractables and leechables. In general, less is preferable although minimizing extractables and leechables is not always as important for some applications. |
| Gravimetric Extractables | A close alternative test method to standard extractables and leechables. The absence or limits of gravimetric extractables are often specified for filtration devices. |
| Heavy Metals | Some filtration materials, such as those derived from cellulose, can be known to possibly contain heavy metals. Polymer resins are often also tested for heavy metal content. The absence or limits thereof are often specified for filtration devices. |
| Integrity Testing | Integrity test specifications will generally be based on bubble point or air diffusion and allow end users to test the integrity and retention of a membrane. |
| Mouse Embryonic Assay (MEA) | A standard test developed to ensure the filtration device has no negative impact on growing cells for embryonic or stem cell applications. |
| Non-Fiber Releasing (Non-Shedding) | Some non-membrane filtration materials are constructed from fibrous materials. As a result many filtration materials, fibrous or not, are tested for this specification and it is sometimes necessary to meet FDA CFR 21 regulations. |
| Non-GMO | Specification related to genetically modified organisms being used in the manufacture of a filter or device. |
| Porosity | The total void volume of the membrane. |
| Pressure | Filtration devices will generally list an operating pressure, burst pressure, or other related specification for the maximum pressure they may be operated to prevent failure. |
| Protein Binding | All membranes bind some amount of protein. In some applications this can be an important selection criteria. Protein binding is typically expressed as BSA binding. |
| Retention | The ability for a membrane to retain target microbes. Retention is expressed as the log reduction of specific microbes at the stated membrane pore size. |
| Shelf Life | The manufacturer’s recommended shelf life will usually be based on the filter type and sterilization procedures. |
| Stem Cell Tested | A manufacturer’s claim that devices are tested to have no negative impact or influence on the culturing of stem cells. |
| Sterility | Many filtration devices are sold sterile. The primary methods are gamma irradiation and contact with ethylene oxide (EtO). Note that gamma should not be used when the application of the filter involves removing the membrane and culturing retained microorganisms for QA/QC. |
| Surface Area | The amount of membrane area. Effective surface area is the amount of usable membrane area within a device. Due to molding or other factors the amount of usable membrane in a device is often less than the amount of membrane used in constructing the device. |
| Symmetry/Asymmetry | A symmetric membrane is uniform throughout its depth. An asymmetric membrane has a changing pore structure throughout its depth allow for different flow rates and holding capacities. |
| Thickness | The overall membrane thickness. Normally expressed in micrometers. |
Click image to enlarge
Thermo Fisher Scientific strives to be a responsible global partner and, to that end, Thermo Fisher Scientific has partnered with My Green Lab and the ACT labeling program to provide transparency with regards to the environmental impact of the products we manufacture and our customers use on a daily basis. ACT labeling provides consumers of laboratory products to make a more informed decision on the impact of their purchases.
Please find an explanation of common filter and filter device specifications below
| Membrane Flow Rate | The speed of fluid passing through a membrane. Pure water is typically used to develop specifications. Flow rate will vary by fluid and processing conditions. Note that device flow rate will be different from the membrane’s flow rate due to the device's effective surface area and properties. |
| Bubble Point (Water Intrusion) | The pressure at which a gas will pass through a wetted membrane. Specifications are typically developed based on pure water and/or a solution of IPA/water. Bubble point is used for integrity testing membranes. Water intrusion is a related term often used for the pressure at which water is pushed from hydrophobic membranes. |
| Component Toxicity | Plastic components are tested for toxicity per USP, FDA and other relevant guidelines. |
| Diffusion | The rate at which a gas will diffuse through a wetted membrane. Typically used for integrity testing of membranes and devices. |
| Endotoxin and Pyrogens | Bacterial endotoxins are typically tested to validate that filtration devices are non-pyrogenic or endotoxin free. |
| Extractables and Leechables | Polymer resins, both membranes and the polymers used in filtration devices, will have some degree of extractables and leechables. In general, less is preferable although minimizing extractables and leechables is not always as important for some applications. |
| Gravimetric Extractables | A close alternative test method to standard extractables and leechables. The absence or limits of gravimetric extractables are often specified for filtration devices. |
| Heavy Metals | Some filtration materials, such as those derived from cellulose, can be known to possibly contain heavy metals. Polymer resins are often also tested for heavy metal content. The absence or limits thereof are often specified for filtration devices. |
| Integrity Testing | Integrity test specifications will generally be based on bubble point or air diffusion and allow end users to test the integrity and retention of a membrane. |
| Mouse Embryonic Assay (MEA) | A standard test developed to ensure the filtration device has no negative impact on growing cells for embryonic or stem cell applications. |
| Non-Fiber Releasing (Non-Shedding) | Some non-membrane filtration materials are constructed from fibrous materials. As a result many filtration materials, fibrous or not, are tested for this specification and it is sometimes necessary to meet FDA CFR 21 regulations. |
| Non-GMO | Specification related to genetically modified organisms being used in the manufacture of a filter or device. |
| Porosity | The total void volume of the membrane. |
| Pressure | Filtration devices will generally list an operating pressure, burst pressure, or other related specification for the maximum pressure they may be operated to prevent failure. |
| Protein Binding | All membranes bind some amount of protein. In some applications this can be an important selection criteria. Protein binding is typically expressed as BSA binding. |
| Retention | The ability for a membrane to retain target microbes. Retention is expressed as the log reduction of specific microbes at the stated membrane pore size. |
| Shelf Life | The manufacturer’s recommended shelf life will usually be based on the filter type and sterilization procedures. |
| Stem Cell Tested | A manufacturer’s claim that devices are tested to have no negative impact or influence on the culturing of stem cells. |
| Sterility | Many filtration devices are sold sterile. The primary methods are gamma irradiation and contact with ethylene oxide (EtO). Note that gamma should not be used when the application of the filter involves removing the membrane and culturing retained microorganisms for QA/QC. |
| Surface Area | The amount of membrane area. Effective surface area is the amount of usable membrane area within a device. Due to molding or other factors the amount of usable membrane in a device is often less than the amount of membrane used in constructing the device. |
| Symmetry/Asymmetry | A symmetric membrane is uniform throughout its depth. An asymmetric membrane has a changing pore structure throughout its depth allow for different flow rates and holding capacities. |
| Thickness | The overall membrane thickness. Normally expressed in micrometers. |
Click image to enlarge
Thermo Fisher Scientific strives to be a responsible global partner and, to that end, Thermo Fisher Scientific has partnered with My Green Lab and the ACT labeling program to provide transparency with regards to the environmental impact of the products we manufacture and our customers use on a daily basis. ACT labeling provides consumers of laboratory products to make a more informed decision on the impact of their purchases.
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