Frequently Asked Questions

B. Membrane filters

What are the differences between "hydrophilic" and "hydrophobic" in the filtration industry?


Hydrophilic filters are easily wet with water. Hydrophilic filters can be wetted with virtually any liquid, and are the preferred filters for aqueous solutions, as appropriate by compatibility. Once wetted, hydrophilic filters do not allow the free passage of gases until the applied pressure exceeds the bubble point and the liquid is expelled from the pores of the membrane. Hydrophobic filters will not be wet in water but will get wet in low surface tension liquids, for instance, organic solvents such as alcohols. Once a hydrophobic filter has been wetted, aqueous solutions also will pass through. Hydrophobic filters are best suited for gas filtration, low surface tension solvents, and venting. In certain applications, hydrophobic filters are used to filter aqueous solutions because of compatibility requirements. Water or aqueous solutions can also pass through a hydrophobic filter once the water breakthrough pressure is reached.




What is a membrane filter?


A membrane filter is a matrix with channels which act as a screen and retains particles larger than the filter on the surface of the membrane. Membrane filters allow the retention of sub-micron particles and organisms.




What is the shelf life of membranes?


To test the membranes, we can perform a "wetting out" test by dipping a small portion of the membrane into water (for hydrophilic) or alcohol (for hydrophobic). If the membrane absorbs the liquid, it has not gone past the shelf life.




What membrane has been used to prevent water from passing, but would allow regular air to pass?


The common membranes used for gas/air filtration are hydrophobic Polypropylene (PP) and PTFE. They both inhibit the flow of water while allowing air to pass. The table below is to show the water intrusion pressure of PTFE membrane which is based on the principle of the smaller the pore size is, the greater intrusion will be.




How is pore size rated?


A pore size rating is determined by the diameter of the particle that can be expected to be retain with a defined, high degree of efficiency. The rating is stated in nominal or absolute terms.




What is the difference between nominal and absolute pore size rating?


Nominal pore size rating describes the ability of the filter to retain the majority of the particles at the rated pore size and larger (60-69%) and cannot be used to compare filters among manufacturers. Glass fiber filters and screen filters are a good example of nominally rated filtration. Processing conditions such as operating pressure and concentration of contaminant have a significant effect on the retention efficiency of the nominally-rated filters. Absolute ratings are used to represents the size of the smallest particle completely retained. Complete retention is within the experimental uncertainty of a standard test method consistent with the intended filter use. Among the test conditions that must be specified are test organism (or particle size), challenge pressure, concentration, and detection method used to identify the contaminant. Most membrane filters are rated as absolute terms.




What is a Polytetrafluoroethylene (PTFE) membrane?


Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer of tetrafluoroethylene that has numerous applications. PTFE is hydrophobic (neither water nor water-containing substances will wet PTFE), as fluorocarbons demonstrate mitigated London dispersion forces due to the high electronegativity of fluorine.

PTFE has one of the lowest coefficients of friction against any solid. Due to its properties, PTFE is often used as a non-stick coating for pans and other cookware. It is also very non-reactive, partly because of the strength of the carbon–fluorine bonds, and so it is often used in containers and pipework for reactive and corrosive chemicals. When used as a lubricant, PTFE reduces friction, wear, and energy consumption of machinery.
Its resistance to highly corrosion chemicals makes it popular for use in the laboratory as containers, magnetic stirrer coatings, and as tubing for highly corrosive chemicals such as hydrofluoric acid, which would dissolve glass containers. It is also used in containers for storing fluoroantimonic acid, a superacid.

PTFE membrane filters are among the most efficient filters used in industrial applications. Filters coated with a PTFE membrane are often used within a dust collection system to collect particulate matter from air streams in applications involving high temperatures and high particulate loads such as coal-fired power plants, cement production, and steel foundries. Its broad chemical compatability also makes it a very versatile filter to use in the lab. PTFE's durability and properties helps it to filter harsh liquids in experiment and gases for protecting both people and expensive equipment.




What is the maximum temperature for the different filter membranes?





What variables affect the performance of a filter?


*Viscosity: The viscosity of a liquid determines its resistance to flow; the higher the viscosity, the lower the flow rate and the higher the differential pressure required to achieve a given flow rate.

*Porosity: The flow rate of a membrane is directly proportional to the porosity of a membrane, eg. the more pores, the higher the flow rate.

*Filter Area: The larger the filter area, the faster the flow rate at a given pressure differential and the larger the expected filter throughput volume prior to "clogging for a given solution."




Can I filter aqueous solutions through a polytetrafluoroethylene (PTFE) hydrophobic membrane?


Yes. However, the membrane requires pre-wetting with an alcohol (such as Isopropanol or Methanol) to establish flow with reasonable pressure differentials.




Which membrane is better? PVDF or Nitrocellulose?


To compare which one is better, we need to take membrane type, pore size, and membrane format into consideration. Physical characteristics: While nitrocellulose is brittle and fragile, PVDF is more durable and has higher chemical resistance making it ideal for reprobing and sequencing applications. Nitrocellulose can prove to be difficult to strip and reprobe without losing signal. However, supported versions of nitrocellulose membranes are considerably more durable and resilient than standard nitrocellulose membranes so they can be stripped, reprobed, and subjected to harsh chemical treatments. Pore size: Both membranes come in typical pore sizes of 0.1, 0.2 or 0.45μm. The 0.45μm membrane is suitable for most protein blotting applications but for smaller peptides or lower molecular weight proteins (less than 15 kD), you should use 0.1 or 0.2μm pore size membrane. Note: When you are detecting a protein loaded at low levels or when quantification is considered critical, you should always choose the smaller size membrane. Membrane format: There are several factors that you need to take into account when choosing the most suitable membrane format, including transfer system (semi-dry, wet or fast), convenience, price and flexibility. Pre-cut and pre-wetted membranes are the ideal choice when convenience, reproducibility and high throughput are of highest importance while rolls offers more flexibility since you can cut the membrane to the specific size of your gel. The only problem is that this can add extra time to your workflow and introduce variability in the membrane size. Pre-cut membranes, on the other hand, are available in a range of sizes suitable for all gel types. Using a precut membrane may result in better transfer reproducibility.




What is a Glass Microfiber filter?


Glass microfiber filters are made of microfiber borosilicate and may or may not have binder. These filters have high filtration efficiency, good chemical stability, and low resistance. Glass microfiber filters can help to increase throughput by filtering out the larger particles before it reaches the main membrane. For high efficiency air filters these become the material of choice. Glass Microfiber filter can be used to produce a separator without clapboard air filters for a variety of fields.




What is the difference between PVDF and PTFE?


As we all may know, PTFE and PVDF membranes are normally hydrophobic. At Finetech, we also carry hydrophilic PTFE membrane filters and syringe filters. The big difference between PTFE and PVDF is that PTFE membranes can be used in the filtration of strong acids and aggressive solutions, but PVDF membranes are more suited for the filtration of non-aggressive aqueous and mild organic solutions. Also there are some similarities between these two membranes. Both membranes have low protein binding ability, can be used for the filtration of gases and air, and they both have good chemical compatibility.




Which chemicals could be used for each membrane?


Please refer to the Membrane Chemical Compatibility Table.





B. Membrane filters

What are the differences between "hydrophilic" and "hydrophobic" in the filtration industry?


Hydrophilic filters are easily wet with water. Hydrophilic filters can be wetted with virtually any liquid, and are the preferred filters for aqueous solutions, as appropriate by compatibility. Once wetted, hydrophilic filters do not allow the free passage of gases until the applied pressure exceeds the bubble point and the liquid is expelled from the pores of the membrane. Hydrophobic filters will not be wet in water but will get wet in low surface tension liquids, for instance, organic solvents such as alcohols. Once a hydrophobic filter has been wetted, aqueous solutions also will pass through. Hydrophobic filters are best suited for gas filtration, low surface tension solvents, and venting. In certain applications, hydrophobic filters are used to filter aqueous solutions because of compatibility requirements. Water or aqueous solutions can also pass through a hydrophobic filter once the water breakthrough pressure is reached.




What is a membrane filter?


A membrane filter is a matrix with channels which act as a screen and retains particles larger than the filter on the surface of the membrane. Membrane filters allow the retention of sub-micron particles and organisms.




What is the shelf life of membranes?


To test the membranes, we can perform a "wetting out" test by dipping a small portion of the membrane into water (for hydrophilic) or alcohol (for hydrophobic). If the membrane absorbs the liquid, it has not gone past the shelf life.




What membrane has been used to prevent water from passing, but would allow regular air to pass?


The common membranes used for gas/air filtration are hydrophobic Polypropylene (PP) and PTFE. They both inhibit the flow of water while allowing air to pass. The table below is to show the water intrusion pressure of PTFE membrane which is based on the principle of the smaller the pore size is, the greater intrusion will be.




How is pore size rated?


A pore size rating is determined by the diameter of the particle that can be expected to be retain with a defined, high degree of efficiency. The rating is stated in nominal or absolute terms.




What is the difference between nominal and absolute pore size rating?


Nominal pore size rating describes the ability of the filter to retain the majority of the particles at the rated pore size and larger (60-69%) and cannot be used to compare filters among manufacturers. Glass fiber filters and screen filters are a good example of nominally rated filtration. Processing conditions such as operating pressure and concentration of contaminant have a significant effect on the retention efficiency of the nominally-rated filters. Absolute ratings are used to represents the size of the smallest particle completely retained. Complete retention is within the experimental uncertainty of a standard test method consistent with the intended filter use. Among the test conditions that must be specified are test organism (or particle size), challenge pressure, concentration, and detection method used to identify the contaminant. Most membrane filters are rated as absolute terms.




What is a Polytetrafluoroethylene (PTFE) membrane?


Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer of tetrafluoroethylene that has numerous applications. PTFE is hydrophobic (neither water nor water-containing substances will wet PTFE), as fluorocarbons demonstrate mitigated London dispersion forces due to the high electronegativity of fluorine.

PTFE has one of the lowest coefficients of friction against any solid. Due to its properties, PTFE is often used as a non-stick coating for pans and other cookware. It is also very non-reactive, partly because of the strength of the carbon–fluorine bonds, and so it is often used in containers and pipework for reactive and corrosive chemicals. When used as a lubricant, PTFE reduces friction, wear, and energy consumption of machinery.
Its resistance to highly corrosion chemicals makes it popular for use in the laboratory as containers, magnetic stirrer coatings, and as tubing for highly corrosive chemicals such as hydrofluoric acid, which would dissolve glass containers. It is also used in containers for storing fluoroantimonic acid, a superacid.

PTFE membrane filters are among the most efficient filters used in industrial applications. Filters coated with a PTFE membrane are often used within a dust collection system to collect particulate matter from air streams in applications involving high temperatures and high particulate loads such as coal-fired power plants, cement production, and steel foundries. Its broad chemical compatability also makes it a very versatile filter to use in the lab. PTFE's durability and properties helps it to filter harsh liquids in experiment and gases for protecting both people and expensive equipment.




What is the maximum temperature for the different filter membranes?





What variables affect the performance of a filter?


*Viscosity: The viscosity of a liquid determines its resistance to flow; the higher the viscosity, the lower the flow rate and the higher the differential pressure required to achieve a given flow rate.

*Porosity: The flow rate of a membrane is directly proportional to the porosity of a membrane, eg. the more pores, the higher the flow rate.

*Filter Area: The larger the filter area, the faster the flow rate at a given pressure differential and the larger the expected filter throughput volume prior to "clogging for a given solution."




Can I filter aqueous solutions through a polytetrafluoroethylene (PTFE) hydrophobic membrane?


Yes. However, the membrane requires pre-wetting with an alcohol (such as Isopropanol or Methanol) to establish flow with reasonable pressure differentials.




Which membrane is better? PVDF or Nitrocellulose?


To compare which one is better, we need to take membrane type, pore size, and membrane format into consideration. Physical characteristics: While nitrocellulose is brittle and fragile, PVDF is more durable and has higher chemical resistance making it ideal for reprobing and sequencing applications. Nitrocellulose can prove to be difficult to strip and reprobe without losing signal. However, supported versions of nitrocellulose membranes are considerably more durable and resilient than standard nitrocellulose membranes so they can be stripped, reprobed, and subjected to harsh chemical treatments. Pore size: Both membranes come in typical pore sizes of 0.1, 0.2 or 0.45μm. The 0.45μm membrane is suitable for most protein blotting applications but for smaller peptides or lower molecular weight proteins (less than 15 kD), you should use 0.1 or 0.2μm pore size membrane. Note: When you are detecting a protein loaded at low levels or when quantification is considered critical, you should always choose the smaller size membrane. Membrane format: There are several factors that you need to take into account when choosing the most suitable membrane format, including transfer system (semi-dry, wet or fast), convenience, price and flexibility. Pre-cut and pre-wetted membranes are the ideal choice when convenience, reproducibility and high throughput are of highest importance while rolls offers more flexibility since you can cut the membrane to the specific size of your gel. The only problem is that this can add extra time to your workflow and introduce variability in the membrane size. Pre-cut membranes, on the other hand, are available in a range of sizes suitable for all gel types. Using a precut membrane may result in better transfer reproducibility.




What is a Glass Microfiber filter?


Glass microfiber filters are made of microfiber borosilicate and may or may not have binder. These filters have high filtration efficiency, good chemical stability, and low resistance. Glass microfiber filters can help to increase throughput by filtering out the larger particles before it reaches the main membrane. For high efficiency air filters these become the material of choice. Glass Microfiber filter can be used to produce a separator without clapboard air filters for a variety of fields.




What is the difference between PVDF and PTFE?


As we all may know, PTFE and PVDF membranes are normally hydrophobic. At Finetech, we also carry hydrophilic PTFE membrane filters and syringe filters. The big difference between PTFE and PVDF is that PTFE membranes can be used in the filtration of strong acids and aggressive solutions, but PVDF membranes are more suited for the filtration of non-aggressive aqueous and mild organic solutions. Also there are some similarities between these two membranes. Both membranes have low protein binding ability, can be used for the filtration of gases and air, and they both have good chemical compatibility.




Which chemicals could be used for each membrane?


Please refer to the Membrane Chemical Compatibility Table.





B. Membrane filters

What are the differences between "hydrophilic" and "hydrophobic" in the filtration industry?


Hydrophilic filters are easily wet with water. Hydrophilic filters can be wetted with virtually any liquid, and are the preferred filters for aqueous solutions, as appropriate by compatibility. Once wetted, hydrophilic filters do not allow the free passage of gases until the applied pressure exceeds the bubble point and the liquid is expelled from the pores of the membrane. Hydrophobic filters will not be wet in water but will get wet in low surface tension liquids, for instance, organic solvents such as alcohols. Once a hydrophobic filter has been wetted, aqueous solutions also will pass through. Hydrophobic filters are best suited for gas filtration, low surface tension solvents, and venting. In certain applications, hydrophobic filters are used to filter aqueous solutions because of compatibility requirements. Water or aqueous solutions can also pass through a hydrophobic filter once the water breakthrough pressure is reached.




What is a membrane filter?


A membrane filter is a matrix with channels which act as a screen and retains particles larger than the filter on the surface of the membrane. Membrane filters allow the retention of sub-micron particles and organisms.




What is the shelf life of membranes?


To test the membranes, we can perform a "wetting out" test by dipping a small portion of the membrane into water (for hydrophilic) or alcohol (for hydrophobic). If the membrane absorbs the liquid, it has not gone past the shelf life.




What membrane has been used to prevent water from passing, but would allow regular air to pass?


The common membranes used for gas/air filtration are hydrophobic Polypropylene (PP) and PTFE. They both inhibit the flow of water while allowing air to pass. The table below is to show the water intrusion pressure of PTFE membrane which is based on the principle of the smaller the pore size is, the greater intrusion will be.




How is pore size rated?


A pore size rating is determined by the diameter of the particle that can be expected to be retain with a defined, high degree of efficiency. The rating is stated in nominal or absolute terms.




What is the difference between nominal and absolute pore size rating?


Nominal pore size rating describes the ability of the filter to retain the majority of the particles at the rated pore size and larger (60-69%) and cannot be used to compare filters among manufacturers. Glass fiber filters and screen filters are a good example of nominally rated filtration. Processing conditions such as operating pressure and concentration of contaminant have a significant effect on the retention efficiency of the nominally-rated filters. Absolute ratings are used to represents the size of the smallest particle completely retained. Complete retention is within the experimental uncertainty of a standard test method consistent with the intended filter use. Among the test conditions that must be specified are test organism (or particle size), challenge pressure, concentration, and detection method used to identify the contaminant. Most membrane filters are rated as absolute terms.




What is a Polytetrafluoroethylene (PTFE) membrane?


Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer of tetrafluoroethylene that has numerous applications. PTFE is hydrophobic (neither water nor water-containing substances will wet PTFE), as fluorocarbons demonstrate mitigated London dispersion forces due to the high electronegativity of fluorine.

PTFE has one of the lowest coefficients of friction against any solid. Due to its properties, PTFE is often used as a non-stick coating for pans and other cookware. It is also very non-reactive, partly because of the strength of the carbon–fluorine bonds, and so it is often used in containers and pipework for reactive and corrosive chemicals. When used as a lubricant, PTFE reduces friction, wear, and energy consumption of machinery.
Its resistance to highly corrosion chemicals makes it popular for use in the laboratory as containers, magnetic stirrer coatings, and as tubing for highly corrosive chemicals such as hydrofluoric acid, which would dissolve glass containers. It is also used in containers for storing fluoroantimonic acid, a superacid.

PTFE membrane filters are among the most efficient filters used in industrial applications. Filters coated with a PTFE membrane are often used within a dust collection system to collect particulate matter from air streams in applications involving high temperatures and high particulate loads such as coal-fired power plants, cement production, and steel foundries. Its broad chemical compatability also makes it a very versatile filter to use in the lab. PTFE's durability and properties helps it to filter harsh liquids in experiment and gases for protecting both people and expensive equipment.




What is the maximum temperature for the different filter membranes?





What variables affect the performance of a filter?


*Viscosity: The viscosity of a liquid determines its resistance to flow; the higher the viscosity, the lower the flow rate and the higher the differential pressure required to achieve a given flow rate.

*Porosity: The flow rate of a membrane is directly proportional to the porosity of a membrane, eg. the more pores, the higher the flow rate.

*Filter Area: The larger the filter area, the faster the flow rate at a given pressure differential and the larger the expected filter throughput volume prior to "clogging for a given solution."




Can I filter aqueous solutions through a polytetrafluoroethylene (PTFE) hydrophobic membrane?


Yes. However, the membrane requires pre-wetting with an alcohol (such as Isopropanol or Methanol) to establish flow with reasonable pressure differentials.




Which membrane is better? PVDF or Nitrocellulose?


To compare which one is better, we need to take membrane type, pore size, and membrane format into consideration. Physical characteristics: While nitrocellulose is brittle and fragile, PVDF is more durable and has higher chemical resistance making it ideal for reprobing and sequencing applications. Nitrocellulose can prove to be difficult to strip and reprobe without losing signal. However, supported versions of nitrocellulose membranes are considerably more durable and resilient than standard nitrocellulose membranes so they can be stripped, reprobed, and subjected to harsh chemical treatments. Pore size: Both membranes come in typical pore sizes of 0.1, 0.2 or 0.45μm. The 0.45μm membrane is suitable for most protein blotting applications but for smaller peptides or lower molecular weight proteins (less than 15 kD), you should use 0.1 or 0.2μm pore size membrane. Note: When you are detecting a protein loaded at low levels or when quantification is considered critical, you should always choose the smaller size membrane. Membrane format: There are several factors that you need to take into account when choosing the most suitable membrane format, including transfer system (semi-dry, wet or fast), convenience, price and flexibility. Pre-cut and pre-wetted membranes are the ideal choice when convenience, reproducibility and high throughput are of highest importance while rolls offers more flexibility since you can cut the membrane to the specific size of your gel. The only problem is that this can add extra time to your workflow and introduce variability in the membrane size. Pre-cut membranes, on the other hand, are available in a range of sizes suitable for all gel types. Using a precut membrane may result in better transfer reproducibility.




What is a Glass Microfiber filter?


Glass microfiber filters are made of microfiber borosilicate and may or may not have binder. These filters have high filtration efficiency, good chemical stability, and low resistance. Glass microfiber filters can help to increase throughput by filtering out the larger particles before it reaches the main membrane. For high efficiency air filters these become the material of choice. Glass Microfiber filter can be used to produce a separator without clapboard air filters for a variety of fields.




What is the difference between PVDF and PTFE?


As we all may know, PTFE and PVDF membranes are normally hydrophobic. At Finetech, we also carry hydrophilic PTFE membrane filters and syringe filters. The big difference between PTFE and PVDF is that PTFE membranes can be used in the filtration of strong acids and aggressive solutions, but PVDF membranes are more suited for the filtration of non-aggressive aqueous and mild organic solutions. Also there are some similarities between these two membranes. Both membranes have low protein binding ability, can be used for the filtration of gases and air, and they both have good chemical compatibility.




Which chemicals could be used for each membrane?


Please refer to the Membrane Chemical Compatibility Table.





F. Other

What are transducer protectors?


Transducer protectors are used in hemodialysis blood lines to keep the blood side of the circuit separated from the machine side and to prevent contamination of the machine by the blood flowing through the circuit. This contamination could be very dangerous and can lead to patient cross contamination with hepatitis B or other viruses. Transducer protectors let air pass while preventing the blood from passing through. TP's incorporate bacterial retentive membrane (0.2µm).
Features:
1. Hydrophobic membrane with 0.2 micron pore size.
2. Prevents contamination of the internal pressure monitoring lines.
3. Antibacterial hydrophobic air filter with female luer lock/male luer lock
4. Custom printed blister packaging available
5. Connects blood tubing to the dialysis machine.
6. Protective hydrophobic barrier allows only sterile air to pass through, protecting patients and equipment from cross-contamination
7. Prevents blood and dialyzing fluids from damaging sensitive transducer monitoring devices.




What is High Performance Liquid Chromatography (HPLC)?


High Performance Liquid Chromatography (HPLC) is a form of column chromatography that pumps a sample mixture or analyze in a solvent (known as the mobile phase) at high pressure through a column with chromatographic packing material (stationary phase). HPLC has the ability to separate, and identify compounds that are present in any sample that can be dissolved in a liquid in trace concentrations as low as parts per trillion. High performance liquid chromatography is now one of the most powerful tools in analytical chemistry. It has the ability to separate, identify, and quantitate the compounds that are presented in any sample that can be dissolved in a liquid. Because of this versatility, HPLC is used in a variety of industrial and scientific applications, such as pharmaceutical, environmental, forensics, and chemicals.




What is the function of air vent filter?


For the safety of the workers and your equipment, always use a vent filter. These devices act as barriers on air lines. They contain hydrophobic media, which prevent the entry of water and aerosols into sensitive equipment and also protect the lab environment from aerosolized pathogens. Vent filters can also enable air to enter and exit vessels such as bioreactors, while maintaining the sterility of the interior environment.




What kind of filter holders are there?


Filter holders are typically either in-line or open-face in design. In-line filter holders have a variety of inlet and outlet connections, and are used in closed filtration systems with either a pressure or vacuum source. In-line filters are ideal for measurement of feed water contamination. They are easy to open and close, and provide a positive, leak-proof seal. Upstream vents, available on some filter holders, allow for the release of trapped gas during liquid filtration. Open-face holders are typically used to take industrial hygiene samples. These holders are easily attached to personal sampling pumps via tubing, with an open inlet surface for impaction of airborne contamination.





B. Membrane filters

What are the differences between "hydrophilic" and "hydrophobic" in the filtration industry?


Hydrophilic filters are easily wet with water. Hydrophilic filters can be wetted with virtually any liquid, and are the preferred filters for aqueous solutions, as appropriate by compatibility. Once wetted, hydrophilic filters do not allow the free passage of gases until the applied pressure exceeds the bubble point and the liquid is expelled from the pores of the membrane. Hydrophobic filters will not be wet in water but will get wet in low surface tension liquids, for instance, organic solvents such as alcohols. Once a hydrophobic filter has been wetted, aqueous solutions also will pass through. Hydrophobic filters are best suited for gas filtration, low surface tension solvents, and venting. In certain applications, hydrophobic filters are used to filter aqueous solutions because of compatibility requirements. Water or aqueous solutions can also pass through a hydrophobic filter once the water breakthrough pressure is reached.




What is a membrane filter?


A membrane filter is a matrix with channels which act as a screen and retains particles larger than the filter on the surface of the membrane. Membrane filters allow the retention of sub-micron particles and organisms.




What is the shelf life of membranes?


To test the membranes, we can perform a "wetting out" test by dipping a small portion of the membrane into water (for hydrophilic) or alcohol (for hydrophobic). If the membrane absorbs the liquid, it has not gone past the shelf life.




What membrane has been used to prevent water from passing, but would allow regular air to pass?


The common membranes used for gas/air filtration are hydrophobic Polypropylene (PP) and PTFE. They both inhibit the flow of water while allowing air to pass. The table below is to show the water intrusion pressure of PTFE membrane which is based on the principle of the smaller the pore size is, the greater intrusion will be.




How is pore size rated?


A pore size rating is determined by the diameter of the particle that can be expected to be retain with a defined, high degree of efficiency. The rating is stated in nominal or absolute terms.




What is the difference between nominal and absolute pore size rating?


Nominal pore size rating describes the ability of the filter to retain the majority of the particles at the rated pore size and larger (60-69%) and cannot be used to compare filters among manufacturers. Glass fiber filters and screen filters are a good example of nominally rated filtration. Processing conditions such as operating pressure and concentration of contaminant have a significant effect on the retention efficiency of the nominally-rated filters. Absolute ratings are used to represents the size of the smallest particle completely retained. Complete retention is within the experimental uncertainty of a standard test method consistent with the intended filter use. Among the test conditions that must be specified are test organism (or particle size), challenge pressure, concentration, and detection method used to identify the contaminant. Most membrane filters are rated as absolute terms.




What is a Polytetrafluoroethylene (PTFE) membrane?


Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer of tetrafluoroethylene that has numerous applications. PTFE is hydrophobic (neither water nor water-containing substances will wet PTFE), as fluorocarbons demonstrate mitigated London dispersion forces due to the high electronegativity of fluorine.

PTFE has one of the lowest coefficients of friction against any solid. Due to its properties, PTFE is often used as a non-stick coating for pans and other cookware. It is also very non-reactive, partly because of the strength of the carbon–fluorine bonds, and so it is often used in containers and pipework for reactive and corrosive chemicals. When used as a lubricant, PTFE reduces friction, wear, and energy consumption of machinery.
Its resistance to highly corrosion chemicals makes it popular for use in the laboratory as containers, magnetic stirrer coatings, and as tubing for highly corrosive chemicals such as hydrofluoric acid, which would dissolve glass containers. It is also used in containers for storing fluoroantimonic acid, a superacid.

PTFE membrane filters are among the most efficient filters used in industrial applications. Filters coated with a PTFE membrane are often used within a dust collection system to collect particulate matter from air streams in applications involving high temperatures and high particulate loads such as coal-fired power plants, cement production, and steel foundries. Its broad chemical compatability also makes it a very versatile filter to use in the lab. PTFE's durability and properties helps it to filter harsh liquids in experiment and gases for protecting both people and expensive equipment.




What is the maximum temperature for the different filter membranes?





What variables affect the performance of a filter?


*Viscosity: The viscosity of a liquid determines its resistance to flow; the higher the viscosity, the lower the flow rate and the higher the differential pressure required to achieve a given flow rate.

*Porosity: The flow rate of a membrane is directly proportional to the porosity of a membrane, eg. the more pores, the higher the flow rate.

*Filter Area: The larger the filter area, the faster the flow rate at a given pressure differential and the larger the expected filter throughput volume prior to "clogging for a given solution."




Can I filter aqueous solutions through a polytetrafluoroethylene (PTFE) hydrophobic membrane?


Yes. However, the membrane requires pre-wetting with an alcohol (such as Isopropanol or Methanol) to establish flow with reasonable pressure differentials.




Which membrane is better? PVDF or Nitrocellulose?


To compare which one is better, we need to take membrane type, pore size, and membrane format into consideration. Physical characteristics: While nitrocellulose is brittle and fragile, PVDF is more durable and has higher chemical resistance making it ideal for reprobing and sequencing applications. Nitrocellulose can prove to be difficult to strip and reprobe without losing signal. However, supported versions of nitrocellulose membranes are considerably more durable and resilient than standard nitrocellulose membranes so they can be stripped, reprobed, and subjected to harsh chemical treatments. Pore size: Both membranes come in typical pore sizes of 0.1, 0.2 or 0.45μm. The 0.45μm membrane is suitable for most protein blotting applications but for smaller peptides or lower molecular weight proteins (less than 15 kD), you should use 0.1 or 0.2μm pore size membrane. Note: When you are detecting a protein loaded at low levels or when quantification is considered critical, you should always choose the smaller size membrane. Membrane format: There are several factors that you need to take into account when choosing the most suitable membrane format, including transfer system (semi-dry, wet or fast), convenience, price and flexibility. Pre-cut and pre-wetted membranes are the ideal choice when convenience, reproducibility and high throughput are of highest importance while rolls offers more flexibility since you can cut the membrane to the specific size of your gel. The only problem is that this can add extra time to your workflow and introduce variability in the membrane size. Pre-cut membranes, on the other hand, are available in a range of sizes suitable for all gel types. Using a precut membrane may result in better transfer reproducibility.




What is a Glass Microfiber filter?


Glass microfiber filters are made of microfiber borosilicate and may or may not have binder. These filters have high filtration efficiency, good chemical stability, and low resistance. Glass microfiber filters can help to increase throughput by filtering out the larger particles before it reaches the main membrane. For high efficiency air filters these become the material of choice. Glass Microfiber filter can be used to produce a separator without clapboard air filters for a variety of fields.




What is the difference between PVDF and PTFE?


As we all may know, PTFE and PVDF membranes are normally hydrophobic. At Finetech, we also carry hydrophilic PTFE membrane filters and syringe filters. The big difference between PTFE and PVDF is that PTFE membranes can be used in the filtration of strong acids and aggressive solutions, but PVDF membranes are more suited for the filtration of non-aggressive aqueous and mild organic solutions. Also there are some similarities between these two membranes. Both membranes have low protein binding ability, can be used for the filtration of gases and air, and they both have good chemical compatibility.




Which chemicals could be used for each membrane?


Please refer to the Membrane Chemical Compatibility Table.





F. Other

What are transducer protectors?


Transducer protectors are used in hemodialysis blood lines to keep the blood side of the circuit separated from the machine side and to prevent contamination of the machine by the blood flowing through the circuit. This contamination could be very dangerous and can lead to patient cross contamination with hepatitis B or other viruses. Transducer protectors let air pass while preventing the blood from passing through. TP's incorporate bacterial retentive membrane (0.2µm).
Features:
1. Hydrophobic membrane with 0.2 micron pore size.
2. Prevents contamination of the internal pressure monitoring lines.
3. Antibacterial hydrophobic air filter with female luer lock/male luer lock
4. Custom printed blister packaging available
5. Connects blood tubing to the dialysis machine.
6. Protective hydrophobic barrier allows only sterile air to pass through, protecting patients and equipment from cross-contamination
7. Prevents blood and dialyzing fluids from damaging sensitive transducer monitoring devices.




What is High Performance Liquid Chromatography (HPLC)?


High Performance Liquid Chromatography (HPLC) is a form of column chromatography that pumps a sample mixture or analyze in a solvent (known as the mobile phase) at high pressure through a column with chromatographic packing material (stationary phase). HPLC has the ability to separate, and identify compounds that are present in any sample that can be dissolved in a liquid in trace concentrations as low as parts per trillion. High performance liquid chromatography is now one of the most powerful tools in analytical chemistry. It has the ability to separate, identify, and quantitate the compounds that are presented in any sample that can be dissolved in a liquid. Because of this versatility, HPLC is used in a variety of industrial and scientific applications, such as pharmaceutical, environmental, forensics, and chemicals.




What is the function of air vent filter?


For the safety of the workers and your equipment, always use a vent filter. These devices act as barriers on air lines. They contain hydrophobic media, which prevent the entry of water and aerosols into sensitive equipment and also protect the lab environment from aerosolized pathogens. Vent filters can also enable air to enter and exit vessels such as bioreactors, while maintaining the sterility of the interior environment.




What kind of filter holders are there?


Filter holders are typically either in-line or open-face in design. In-line filter holders have a variety of inlet and outlet connections, and are used in closed filtration systems with either a pressure or vacuum source. In-line filters are ideal for measurement of feed water contamination. They are easy to open and close, and provide a positive, leak-proof seal. Upstream vents, available on some filter holders, allow for the release of trapped gas during liquid filtration. Open-face holders are typically used to take industrial hygiene samples. These holders are easily attached to personal sampling pumps via tubing, with an open inlet surface for impaction of airborne contamination.





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Since 1999, Finetech is the leading Taiwanese manufacturer of syringe filters and offers a wide range of products for environmental, pharmaceutical, life science, and other laboratories.

*All images used are for illustrative purposes only. Actual color may vary due to lighting, enhancements, or monitor setting.