filter

Filter membrane classification

At present, the membrane separation technology mainly includes microfiltration, ultrafiltration, nanofiltration and reverse osmosis, which is a membrane process driven by pressure difference. When there is a certain pressure difference on both sides of the membrane, a part of the solvent and the components smaller than the membrane pore size can penetrate the membrane, and the particles, macromolecules, salts, etc. are trapped by the membrane, so as to achieve the purpose of separation. The difference mainly lies in the size of the particles or molecules to be isolated and the structure and performance of the membrane used.

Microfiltration membrane is an important part of membrane separation technology, and the main principle is screening. Microfiltration is between conventional filtration and ultrafiltration, usually intercepting particles with a particle size greater than 0.05μm, and the pore size of the membrane ranges from 0.1 to 10μm. The symmetrical microporous membrane is mostly used to realize the separation of solid particles and colloidal particles from the solvent, and is often used as the pretreatment step of ultrafiltration.

Commonly used microporous filter membrane

The use of microporous filter membrane filtration is one of the common methods for the pre-treatment of small samples. It uses different materials and pore sizes as filter media to remove small insoluble particles in the sample to obtain clear solutions. In HPLC and HPLC-MS/MS analysis, the filtration operation of the sample pretreatment process is essential. One is to avoid the blockage of the system and prolong the service life of the column. Second, it can eliminate the pressure fluctuations caused by the friction of small particles and the baseline fluctuations caused by irregular impurities, thus interfering with the sample detection.

PES

"It is a polysulfone, a hydrophilic film that has excellent chemical resistance to inorganic reagents (suitable for the filtration of low inorganic ion solutions) and acid and base, but cannot tolerate strong polar solvents (ketones, esters, and oils)." Compared with other membrane varieties, PES membranes are characterized by very low protein adsorption capacity, no contamination of samples, and high throughput. It is widely used in the preparation of biological samples, microbial industry, pharmaceutical filtration and routine filtration.

Nylon

"It belongs to the polyamide class and is a naturally hydrophilic condensed polymer used for filtration of alkaline solutions and most organic solvents." Nylon membrane has very good mechanical strength, good chemical stability, high adsorption (generally not used for biological sample filtration, so as not to lose the sample due to adsorption). When used for chromatographic analysis of mobile phase filtration, nylon is more economical than PTFE membrane, is the most economical choice for the laboratory, not only can be applied to the filtration of hydrophilic samples, some organic solvents (acetonitrile, alcohols, dimethyl sulfoxide, etc.) can also be tolerated.

PTFE

Is a fluoropolymer, both hydrophilic and hydrophobic, known as the universal membrane, the most extensive chemical compatibility, can resist a variety of solvents, has good biocompatibility, suitable for almost all organic solutions (tolerance to DMSO, THF, DMF, dichloromethane, chloroform and other strong solvents), hydrophilic acid, strong alkali filtration, In particular, solvents that are not tolerated by other filters.

PVDF

It is a fluoropolymer that is both hydrophilic and hydrophobic. It has good heat resistance (-40℃-150℃ long-term use) and chemical stability. The absorbency of hydrophilic filter membrane is much smaller than that of CN, Nylon and PTFE membrane, which can be applied to the filtration of biological samples and culture media, chemical reagents and raw materials. Hydrophobic filter membrane is suitable for gas, steam, high temperature liquid filtration; However, they could not tolerate acetone, DMSO, THF, DMF, dichloromethane and chloroform.

MCE

"A hydrophilic film made of cellulose nitrate and cellulose acetate, which is biologically inert, has uniform pore size, thin texture, small resistance, high filtration rate, minimal adsorption, and high biological inertness, and is not resistant to strong acids, bases, and organic solvents." It is applied to filter general water soluble samples (PH5-10), such as routine biochemical analysis, microbiological and sterility testing.

It is a polyolefin made of polypropylene microfiber hot melt adhesion, which is used for deep filtration. Chemical stability, resistance to high temperature, organic solvents and strong acid and alkali, generally used for solid-liquid separation.

With hydrophilic, weak acid resistance, high protein adsorption capacity, used in medical laboratory and diagnosis of bacterial culture and bioengineering, trace element analysis, biochemical analysis (electrophoresis, biological macromolecular blotting, immune kit, etc.).

· Aperture of filter membrane

· In the specific experiment, the appropriate pore size filter membrane and filter should be selected according to the requirements of the filtration purpose experiment. Commonly used filter membrane pore sizes are 0.10μm, 0.22μm, 0.45μm, 0.8μm, 1.0μm;

· 0.1μm: can remove mycoplasma in the sample;

· 0.22μm: can remove 99.99% of bacterial microorganisms, meet the requirements of GMP or pharmacopoeia in the removal of bacteria, but also can remove samples, mobile phase of the extremely fine particles, suitable for the treatment of solvent samples with higher requirements, such as UPLC, mass spectrometry, etc., if the particle size of the column is less than or equal to 3μm, recommended to use 0.22μm pore size filter membrane;

· 0.45μm: can filter most bacteria, routine samples, flow equal filtration, can meet the general chromatographic requirements, for HPLC system, the particle size of the column is more than 3μm, 0.45μm pore size filter membrane can be used;

· 0.8μm: suitable for the analysis and detection of more insoluble drug excipents, suspensions and adhesives, with relatively low sample requirements;

· > 1.0μm: can filter large particles of impurities or difficult to handle, turbidity sample pretreatment, after pretreatment, select the corresponding filter membrane for filtration.

matters need attention

1. The appropriate filter membrane should be selected according to the chemical compatibility of the filtrate before use.

2, if the water filter membrane, using the organic phase of the filter membrane, your liquid pumping filter can not go down, the use of organic membrane with water filter membrane, your filter membrane will be dissolved, dissolved in the filter membrane solvent is strictly prohibited into HPLC.

3. The filter membrane has both sides. The more reflective side is the positive side, and the less reflective side is the negative side.

4. Do not sterilize the filter frame together with the filter membrane, otherwise the filter membrane will be brittle and wrinkled due to thermal expansion and cold contraction.

5. In the analysis field, it is necessary to pay attention to whether new impurities are introduced after filtration of the filter membrane.