Do You Know How To Choose A Membrane Filter?
In the laboratory, no matter it is an inorganic experiment, organic experiment, or physical and chemical experiment, overkill operation is essential. How to choose the filter membrane and filter reasonably and quickly is a skill that every experimental worker must master.
Recognize the importance of filtering. Filtering protects chromatographic systems and columns, prolongs their service life, and improves the accuracy of data. Filtration eliminates pressure fluctuations due to friction particles and baseline fluctuations due to irregular impurities. The interference of bubbles to the detection system can be eliminated.
Therefore, a membrane filter is usually used to filter the mobile phase and a syringe filter is used to filter the sample. Let us know the related parameters and common sense of membrane filter first.
Related parameters and common sense of membrane filter
1. Absolute aperture
The absolute pore size class is defined by identifying pore size by 100% interception of challenging bacteria of a particular size under very stringent test conditions. Among the conditions that must be specified are the measurement of organic (or molecular) size and concentration, measurement of pressure, and inspection.
2. Air flux
Is a method of measuring air passing through a filter. That is, in the case of different pressure, different porosity, and different device area, the flow of air through.
3. The bubble point
In the microporous membrane industry, the use of a specific liquid to wet the roll membrane, and at a specific temperature, the need to squeeze out of the membrane hole liquid minimum pressure.
4. Filter function
Filters are defined in terms of their overdose and blocking particle size at specific pressures. In general, the lower the obstruction and pressure, the more effective the filter.
5. Filter material life
Maximum lifetime of the filter under certain operating conditions. It depends on many factors, such as the nature of the filtrate, the operating temperature, and the choice of filter material.
6. Hydrophobic and hydrophilic membrane
Hydrophilic membrane filter usually has a special chemical layer that allows the membrane to be infiltrated by water; Hydrophobicity is a reference for repulsion to water. Hydrophobic membrane filter rarely do not absorb water at all. In observation, small droplets of water can be seen to stay on the surface of the filter membrane without being absorbed by the surface and diffused into the water surface. The size of hydrophobicity depends on the aperture of the filter material and the characteristics of the membrane filter material.
7. Flow rate and pore rate
Flow rate is the amount of filtrate passing through the membrane per unit of time at a specific temperature and pressure. The flow rate is closely related to the surface properties of the membrane filter. Flow rate and pore rates are two important parameters of filter material and design performance. This performance depends on the following aspects :
(1) Viscosity: viscosity determines the flow of the liquid. The higher the viscosity of the liquid (at a given temperature and pressure), the lower the flow rate. The higher the pressure required to achieve the same flow rate.
(2) Pressure difference the pressure difference between inlet and outlet infiltration. When the filter is fully loaded, the filtration pressure difference increases.
(3) Pore rate: refers to the proportion of the volume of all holes in the filter membrane to the total volume of the filter membrane. Usually, the filter membrane has a 50-90% pore area, and the flow rate is directly related to the pore rate of the membrane.
Then, the following factors should be considered in the selection of the filter membrane:
1. Filter material of the filter membrane
When choosing a filter membrane, chemical compatibility should be considered first. Is the filter resistant to acid, alkali, organic solvents, etc?
2. The pore size of the filter membrane
For chromatographic column systems using fillers of 3um or greater size, a 0.45um needle filter or filter membrane can be used. For chromatographic systems with fillers less than 3um or involving microbial growth, a 0.2um filter is recommended. For the difficult turbidity solution, a 1-5um filter membrane can be used for pre-filtration, and then the corresponding filter membrane can be used for further filtration.
3. Characteristics of samples
(1) Water-borne sample: water-wet diaphragm is selected. It has an affinity for water and is suitable for filtering water-based solutions. Available filter membranes are mixed cellulose membrane, polyethersulfone (PESM), NylonM, etc.
(2) Highly corrosive organic solvents: generally using a hydrophobic membrane.
(3) Protein solution: choose the filter membrane with low protein adsorption, such as the PVDF filter membrane.
(4) Ion chromatography: PES filter membrane is generally considered to be suitable for filtration of solutions with low inorganic ions.
4. When selecting a syringe filter
In addition to the above factors, consider the sample size (that is, the size of the needle filter to choose): usually, if the sample size is less than 2ml, a miniature filter head with a diameter of 4mm should be selected. The sample size is between 2 and 10ml, and a filter head with a diameter of 13mm is selected. When the sample size is greater than 10ml, a filter head with a diameter of 25mm is selected.
Click here to know Working Principle of Membrane Filter