Membrane filter is a kind of polymer filter membrane material, with many uniform micropores, membrane filter pore size ranging from 0.025 to 14μm, and its filtration mechanism is mainly physical sieving. There are many types of microporous membranes, commonly used are cellulose acetate membranes, polypropylene membranes, and polytetrafluoroethylene membranes.
The advantages of filter membrane are high porosity, fast filtration speed, small adsorption, no retention of liquid medicine, no influence on drug content, simple equipment, easy removal, etc.
The disadvantage of filter membrane is poor acid and alkali resistance, and poor adaptability to certain organic solvents such as propylene glycol. The trapped particles can easily block the filter membrane and affect the filtration rate. Therefore, the membrane can be used for filtration after preliminary filtration with other filters.
Filter membranes are divided into organic membranes and water membranes. Organic membranes can pass aqueous solutions, while water membranes cannot pass organic solutions. There are different aperture specifications. Some have a smooth and rough surface, and some have no front and back. Generally, when filtering, discard the first filtrate of 2,3ml, so as not to interfere with the detection of filter membrane impurities. After adopting the filtration step, check whether the filter membrane has adsorption of drugs.
For the diaphragm used for analysis: Imported microporous membranes are the same on both sides, domestic membranes are smooth on one side and slightly rough on the other side, but domestic membranes have no positive and negative sides. Because microporous membranes are symmetrical membranes, both sides have the same effect. The filter membrane is produced by coating the membrane liquid on the glass plate, and the glass side is smooth.
But there are special circumstances: As a filtration product in large-scale production, many sample filter membranes distinguish between positive and negative: if the reverse is used, the filtration capacity will be greatly reduced, but the positive and negative sides are generally marked by the manufacturer.
The microporous filter membrane for filtering the solvent has a special suction filter bottle. When the organic solvent content does not exceed 5%, use a water membrane. Otherwise, the organic membrane is used to filter the sample with a syringe. First, draw the solution with a needle and pull out the needle. Replace the filter membrane, first put 2-3 drops in the waste liquid and then filter into the sample.
How to use microporous membrane filter?
1. Selection of microporous membrane filter. According to the solvent to be filtered, select the microporous membrane of suitable material and specification to open the package in the clean area. For example, if the solvent to be filtered is a strong acid or a strong base, hydrophilic PTFE membrane filter is used.
2. Check the selected microporous membrane. After selecting the filter membrane, carefully check the filter membrane for holes, cracks, and foreign matter on the membrane. Due to the improvement of the production process of the microporous membrane, the quality of the current microporous membrane, whether domestic or imported, is relatively good, and the above situation will not occur.
3. Immersion of the microporous membrane. Use distilled water to rinse several times before the microporous filter membrane, soak it in water for injection for one day to make the microporous filter membrane achieve the best effect.