3 Main Factors to Be Considered When Purchasing Syringe Filter

The correct choice of a syringe filter with the right performance is essential to obtain fast and accurate results. But with so many syringe filters available, how can you be sure you are making the right choice? HAWACH is here to help you make the right choice by providing an overview of the basic functions and classifications of syringe filter and its filter membranes. There are three main considerations for the syringe filter: material, diameter and pore size.

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1. Syringe filter membranes' materials

Unlike deep filtration products made from cotton and fiberglass, membranes are traditionally classified as surface filtration products because they retain particles almost completely on the surface of the membrane, just like a screen. Membranes are capable of retaining particles down to 0.015 μm and can retain submicron particles and microorganisms. The main applications of membranes are in water microbiology and air pollution monitoring. Filter membranes can be classified as hydrophilic or hydrophobic. For the hydrophilic membranes: because hydrophilic membranes have hydrophilic groups, almost any liquid can wet the membrane, and they are typically used for aqueous solutions and organic solvents that are water-soluble. For the hydrophobic membranes, the hydrophobic filter media are suitable for filtering organic solvents or for ventilation and gas filtration. Depending on the material, membranes can also be classified as CA, CN, Nylon, PTFE, GF and so on.

Cellulose acetate membranes (CA) have high flow rates and thermal stability and very low adsorption. 0.2 μm membranes are well suited for decontamination of aqueous solutions, buffers, serum and culture media. 0.45 μm membranes are well suited for mobile phase filtration for HPLC. Obtaining published results on membrane adsorption is difficult and is related to the substances filtered, the conditions of filtration and the assay method used, as well as the fact that the membrane being assayed was not pre-decontaminated.

Cellulose nitrate membranes (CN) are very good filter membrane materials that provide very consistent pore size structures and wide pore size specifications. Large pore sizes (8μm, 5μm and 3μm) are used for chemotaxis and cell retention, 0.45μm for particle collection, and the smallest pore size (0.1μm) is used for ultraclean filtration of solutions and light scattering measurements. The non-specific adsorption properties of this type of membrane make it very suitable for many blotting processes and diagnostic reagent applications. They are used for sample pretreatment, particle detection or particle removal.

Polyamide and Nylon membranes have very good mechanical strength, strong adsorption properties and are resistant to most organic solvents and most alkaline solutions, making them particularly suitable for filtration of alkaline solutions. For organic solvent filtration, such as HPLC mobile phase de-particulation filtration, nylon membranes are more economical and practical than PTFE membranes, and in addition, nylon membranes can be used as transfer membranes. Due to the relatively high adsorption properties of nylon membranes, they are generally not recommended for culture media filtration, or filtration of biological samples such as protein fluids, to avoid loss of samples due to adsorption. In such cases, cellulose acetate (CA) membranes with low adsorption are usually used and are more suitable for organic and alkaline solutions filtration.

PTFE Membranes ensure the unimpeded passage of moist air or other gases even at very low differential pressures, while aqueous solutions are not permeable. PTFE membranes are extremely chemically compatible and are capable of filtering virtually all organic solvents and highly corrosive chemicals. When aqueous solutions must be filtered through PTFE membranes, they must be pre-wetted with ethanol or isopropyl alcohol before the aqueous solution can be filtered through. It is mainly used for the filtration of air, gases and hydrophobic chemicals.

Glass fiber membrane (GF) is mainly used as a filtration layer, directly on the membrane, to improve filtration throughput and continuous filtration, which is deep filtration. It is important to note that different sizes of filters have specific requirements for the diameter of the prefilter membrane, and if the diameter is too large, the edge will reach under the seal and cause leakage.

2. Syringe filter membranes' diameter

The diameter of the piece, at present, the more frequently used are 13mm and 25mm. According to the volume of the sample to choose the corresponding diameter:for samples 2 ~ 10mL, choose 13mm; for 10mL ~ 100mL, choose 25mm; for more than 100mL, 33mm can be considered. The specifications mainly focus on 0.22μm and 0.45μm, of course, other non-conventional specifications are also available for sale.

3. Syringe filter membranes' pore size

So how to choose the pore size? Among them, 0.22μm can remove very fine particles in the sample and mobile phase, and is suitable for chromatography system with less than 3μm packing; 0.45μm pore size is mainly for regular sample and mobile phase filtration, which can meet the general chromatography requirements, and is suitable for chromatography column system with 3μm or larger packing; for difficult turbid solution, 1-5μm filter membrane can be used for pre-filtration, and then use the corresponding membrane for continuous filtration.

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