Syringe filter
A syringe filter, or syringe filter for short , is used as an attachment in front of a disposable syringe for clarifying or sterile filtration of small volumes of a solution ; pore sizes of 0.45 µm or 0.2 µm are usually used. To do this, the solution in the syringe is pressed through the membrane filter of the syringe filter (pressure filtration). A typical area of application is sample preparation for chemical analysis using chromatographic methods such as high-performance liquid chromatography (HPLC). In addition, syringe filters are used for the sterile filtration of solutions with thermally unstable ingredients, which are then added to a nutrient medium that has been steam-sterilized in the autoclave . A big advantage compared to other filtration methods is the low dead volume that remains in the filter.
construction
The syringe filter consists of a porous flat membrane that is held in a plastic filter housing . Chemically resistant polypropylene or polyamide is usually used as the housing material. In some cases, less resistant but transparent polycarbonate is used. The filter is usually provided with a female Luer lock connection on the inlet side , which is screwed directly into the disposable syringe and prevents slipping during pressure filtration. On the outlet side, a male Luer-Slip connection is usually sufficient, as the forces that occur here are significantly lower.
Upper and lower part of the filter housing either through ultrasonic each other are welded , or the outer edge is encapsulated. Colored polymers are often used for overmolding in order to be able to differentiate between different syringe filters more easily.
Selection criteria for syringe filters
Sample size and viscosity
The appropriate filter area or the filter diameter depends on the amount of solution to be filtered, the proportion of solids and the viscosity of the medium. For low-viscosity (e.g. aqueous) media with low solids content, the following table can be used as a rough rule of thumb (exact values depend on the design or geometry of the filter). In the case of media with a higher viscosity or a higher proportion of solids, it makes sense to choose a larger filter diameter. The same applies to very small pore sizes or when rapid filtration is required. However, the dead volume increases with the filter diameter, i.e. H. the amount of liquid that remains in the filter after filtration.
| Sample amount | Filter diameter | Filter area | Dead volume |
|---|---|---|---|
| <1 ml | 3-4 mm | <0.07 cm² | 5 µl |
| 1-10 ml | 13-15 mm | 1.3-1.7 cm² | <25 µl |
| 10-100 ml | 25 mm | 4.8 cm² | <150 µl |
| > 100 ml | 30 mm | 7 cm² | <200 µl |
Pore size
The pore size of the membrane determines the purity of the liquid after filtration. The most frequently used syringe filters have a pore size of 0.45 µm or 0.2 µm. A clear filtration with a pore size of 0.45 µm is suitable for a measurement with high-performance liquid chromatography (HPLC) in order to prevent the separation column from clogging with particles. For UHPLC , however, a finer pore size of 0.2 µm makes sense.
In the microbiological laboratory or in the cell culture laboratory , the aim is to remove bacteria from a solution with thermally unstable ingredients (e.g. vitamins or antibiotics ), as these cannot be steam-sterilized with an autoclave at 121 ° C. For sterile filtration of a volume of up to 100 ml, syringe filters with a pore size of 0.2 µm or 0.45 µm are used; viruses and mycoplasmas are not retained with either pore size . The so-called “Bacteria Challenge Test” provides information on which types of bacteria are retained with a syringe filter of a certain pore size (see section on pore size and selectivity in the article on membrane technology).
Filters with a pore size of 5 µm correspond to a pre-filtration in order to filter out larger fractions. Pre-filtration is particularly useful when there is a high proportion of solids, which would immediately clog a fine filter membrane. Some syringe filters therefore contain a pre-filter made of a glass fiber fleece or a fleece made of PP fibers in the same filter housing above the fine filter membrane .
Chemical and physical properties of the membrane
As the actual filter, membranes are made of various materials such as B. polyamide (PA), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), cellulose acetate (CA), regenerated cellulose (RC), polypropylene (PP), cellulose mixed ester (CME) and polyethersulfone (PES) are used. These have different sensitivity to solvents. The resistance to acids, alkalis, organic or even halogenated solvents is very different for the materials available. If very sensitive measurements take place after the filtration, it must also be ensured that no substances are washed out of the filter. When using biological samples, attention should be paid to the different strengths of protein adsorption by different filter materials. Many syringe filters are available in both non-sterile and sterile versions. Most manufacturers provide lists of chemical resistance and material properties.
Web links
- Selection guide for syringe filters - all manufacturers. (Video) In: Youtube. Altmann Analytik, July 24, 2016, accessed December 9, 2019 .
Individual evidence
- ↑ Joachim Podlech (Ed.): Working methods in organic chemistry: With an introductory program . 3. Edition. Lehmanns Media, Berlin 2014, ISBN 978-3-86541-618-6 , pp. 148 ( google.de [accessed December 8, 2019]).
- ↑ a b c Eckhard Bast: Microbiological methods: An introduction to basic work techniques . 2nd Edition. Spectrum Akademischer Verlag GmbH, Heidelberg / Berlin 2001, ISBN 978-3-8274-1072-6 , p. 24-29 .
- ↑ a b c d your filtration solution. (PDF) Graphic Controls, DIA-Nielsen GmbH & Co. KG, accessed on December 8, 2019 .
- ↑ a b c d Volker Lorbach: Selection guide syringe filters. (PDF) ISERA GmbH, May 2, 2017, accessed December 8, 2019 .
- ↑ a b Sartorius laboratory catalog. Satorius AG, 2005, accessed December 8, 2019 .
- ↑ Altmann Analytics: Selection guide for syringe filters - all manufacturers. Accessed December 8, 2019 (German).
- ↑ Heribert Keweloh, Linda Frintrop: Molecular biology and microbiology: basic knowledge and laboratory methods . 1st edition. Verlag Europa-Lehrmittel, Haan-Gruiten 2016, ISBN 978-3-8085-6973-3 , p. 393-394 .