Pore Size, Materials, and Use Notes of Filter Membranes

Microporous filter membranes are made by using polymeric chemical materials and porogenic additives that are specially treated and coated on the support layer. In the application of membrane separation technology, microporous filter membrane is a membrane species with a wide range of applications, which is easy to use, fast, and features wide applications. It is hydrophilic, non-toxic, and hygienic, and is a porous membrane filter material with a relatively uniform pore size distribution of penetrating microporous. Today, HAWACH will mainly introduce the frequently used filter membranes and their use notes.


Frequently used filter membranes( based on pore size)

There are four kinds of filter membranes used frequently, with pore sizes of 0.22μm, 0.45μm, 0.8μm, and 1.0μm.

1) 0.22μm filter membrane

It can remove the requirements of extremely fine particles in samples and mobile phases; it can meet the requirements of GMP or Pharmacopoeia for 99.99% sterilization. Suitable for the processing of solvents and samples with high and higher requirements, such as ion-pair reagents for chromatography, and ultrapure. Water, mass spectrometry analysis solvent samples, etc. filtration. For less than 3μm, 3μm or larger packed color chromatography system.

2) 0.45 μm filter membrane

Can filter out most bacteria and microorganisms, is suitable for routine samples, and mobile phase filtration, and can meet general chromatography requirements

3) 0.8-1.0 μm filter membrane

Removal of most insoluble particles, suitable for ultraviolet (UV) and other relatively low demand for the sample yo detection, higher efficiency than 0.45μm membrane, especially for insoluble excipients, suspensions, and binders, and the use of UV detection of oral solid formulations dissolution detection.

4) 1-5μm filter membrane

Filtration of larger impurities or pretreatment of turbid solutions that are difficult to handle can be done with 1-5μm membranes before filtration with the corresponding membrane.

Frequently used filter membranes( based on materials)

Microporous filter membranes mainly include cellulose acetate filter membranes, mixed cellulose ester filter membranes, nylon filter membranes, polytetrafluoroethylene filter membranes, polyvinylidene fluoride membranes (PVDF), polyethersulfone filter membranes, polypropylene filter membranes (PP filter membrane). It can be divided into hydrophilic system, organic system (filtered water system requires pre-wetting (ethanol)), and hydrophilic system organic general (organic resistance, filtered water system does not require pre-wetting).

Use notes of filter membrane

1. Before using the microporous filter membrane, it should be cleaned and treated, soaked and washed with distilled water, and then installed in the filter, while the filtration of organic solvent is washed with ethanol immersion. For the filtration of spectrum samples or, if it is aqueous, distilled water is washed and soaked, then distilled water is pre-filtered, if organic filtration, the product is first soaked in pure toluene and above 95% ethanol respectively overnight, then pure toluene and pure ethanol are pre-filtered, and the membrane is washed and used.

2. The filter membrane before use must be accurately selected according to the needs of the membrane pore size, the substances to be filtered out must be greater than the pore size of the membrane.

3. If using it on demanding occasions, such as the filtration of chromatography samples or reagents, wash with distilled water and then pre-filter with distilled water for the water system. Soak the product in pure toluene and 95% or more ethanol overnight, then pre-filter with pure toluene and pure ethanol, wash the membrane, and use, for the organic system filtration. The product becomes brittle significantly after entering water, and the reduction of strength in organic solvents is lighter.

4. If filtrate with more particles or bacteria, it should be pre-filtered, that is, pre-filtration media or large pore size membrane filter first, to avoid too fast clogging.

5. Disinfection: The membrane is not disinfected before leaving the factory, so it needs to be sterilized before use. Disinfection in many ways, generally using hot-pressure sterilization, that is 121 °C steam sterilization for 30 minutes. In hot-pressure sterilization, steam should be avoided directly one-way rush on the membrane to prevent negative pressure due to steam condensation and the back of the membrane under pressure and breakage boiling sterilization, chemical disinfection, etc. can also be used for sterilization and filtration with bubble method to test whether the seal is tight, whether the membrane is broken due to improper sterilization. If you have any questions about the disinfected ones, pls contact HAWACH.

6. When filtering liquid, the membrane must be wetted. Apply sterile water to wet it, if it becomes dry due to disinfection. If the wetting is not good to affect the flow rate, before sterilization and filtration, the membrane must be sterilized for all appliances, and then in the sterile room for sterilization and filtration, it should be strictly in accordance with the sterilization operating procedures.

7. The microporous filter membrane is flammable and not acid and alkali-resistant, not solvent resistant, only for aqueous solution (PH5-10) oil, air, juice, wine, etc.

8. When using pressure, vacuum, and potential difference, we must pay attention to prevent the outside air in the vacuum from bacteria, and particles from inhaling contaminated filtrate, in pressurized filtration, the faster filtration speed, the higher the pressure, the faster the filtration speed, high pressure should consider whether the filter support body is intact.

9. In pharmaceutical analytical dissolution experiments, membrane adsorption is the most common drawback of using microporous filter membranes. There are many factors affecting membrane adsorption, including the diameter of the membrane, pore size, material, type of filter medium, ionic strength, pH, and the nature of the drug itself. The interaction forces such as hydrogen bonding, van der Waals forces, and charge adsorption between different materials of filter membranes and different compounds being filtered vary, and the degree of adsorption varies. It has also been reported in the literature that different pH buffer salts and different diluents (e.g. methanol) can reduce or eliminate adsorption.

10. In drug analysis of substances of interest experiments, attention needs to be paid to whether new impurities are generated after membrane filtration.