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. Microfiltration (MF)0.1 - 5.0 micron Ultrafiltration (UF)0.01-0.1micron Nanofiltration (NF) Reverse Osmosis (RO) 0.001micron (theoretical)

2.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.

3.What is the shelf life of membranes?

Membranes Shelf life Cellulose acetate (CA) 2.5 – 3 years Nitrocellulose (MCE) 2.5 – 3 years Nylon No shelf life 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.

4.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. Water intrusion of PTFE Pore size (um) 0.2 0.45 1.0 3.0 5.0 Water intrusion pressure (psi) 40 20 7 2 1

5.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.

6.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.

7.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.

8.What is the maximum temperature for the different filter membranes?

Membrane / Temp. Polyester /140°C PTFE (Laminated) /130°C PTFE (Unlaminated)/260°C Nylon180°C MCE/130°C PES/180°C Polypropylene/82°C Silver Metal /427°C

9.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."

10.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.

11.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.

12.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.

13.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.

14.What is a PTFE Membrane?

Polytetrafluoroethylene (PTFE) membrane filter is made of polytetrafluoroethylene, which is expanded and stretched to form a microporous membrane. It's available in hydrophilic, hydrophobic, unlaminated, and laminated options for a wide range of applications and temperatures. Polytetrafluoroethylene (PTFE) membranes are resistant to high temperatures, strong acids, strong alkalis, organic solvents, and oxidants. It is chemically compatible and resistant to most chemical solvents and chemically stable and inert, suitable for chemically corrosive organic solvents, aqueous solutions, and gases, and has resistance to most acids, alkalis, and solutions.

15.What is the difference between hydrohobic and Hydrophlic ?

The polytetrafluoroethylene (PTFE) membrane is an inlet membrane, a hydrophobic membrane filter, which is treated with ethanol or isopropanol to become a hydrophilic membrane filter. The hydrophobic nature of PTFE promises its long-lasting unwetted status even be kept contacting with water or other normal liquids, and the open porous structure provides a wide range of pore size, 0.02μm to 10μm, ensuring the retention of bacteria, virus, and particles is always effective while maintaining the excellent gas permeability. Naturally hydrophobic; they are very useful for aerosol sampling, air venting, and gas filtration, especially in environments also containing water vapor. Hydrophilic PTFE membrane is made of pure PTFE membrane bonded to a polypropylene non-woven support. The extreme chemical compatibility makes it an ideal material for filtration of almost all solvent, acids and alkaline solutions, and organic-based aqueous samples, and is commonly used for HPLC solvents sample preparation. The membrane is super-clean, promises low residual contamination added to the flux during the clarifying process, ensuring the analysis is not disturbed and the results are accurate. membrane have highly excellent corrosion resistance, high flow rate and other characteristics, which can be widely used in various filtration needs, such as Industrial wastewater, laboratory drugs, semiconductor cutting fluid, aquaculture and fishery, food processing, livestock wastewater, etc.