What type of syringe filter should you be using?

In the world of laboratory filtration, syringe filters are vital tools for achieving sample purity and clarity. These disposable devices efficiently remove impurities and particulate matter from liquids or gasses, ensuring that your results are reliable and accurate.

However, there are various types of syringe filters available, each with specific features for different use cases. If you’re wondering which filter is best suited for your application, read on to learn more about what syringe filters do, how to choose between them and when to use each one for the best results, helping make sure you’re fully informed before you buy.

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What are syringe filters?

A syringe filter is a small, disc-shaped filtration device that is designed to be attached to a syringe. It consists of a housing and a single-use membrane, which means it must be disposed of after each use and cannot be reused. The membrane can be made from a variety of materials which can alter the intended purpose of the filter - making it more suitable for liquids rather than gasses, for example. Both the housing and the membrane must be suitable for the application in order for the device to work correctly and trap unwanted particles and contaminants as they pass through.

What is a syringe filter used for?

Syringe filters are widely used in various laboratory applications where sample purity is vital for accurate work. Some common uses include:

Biomolecular purification

In biomolecular analysis, it is often necessary to access isolated samples of biomolecules such as proteins, lipids, and nucleic acids. Syringe filters effectively remove any contaminants to ensure the sample’s purity.

Clarification

Syringe filters are used to remove particulate matter, such as sediment, from liquid samples. This ensures clarity of the solution and prevents clogging of analytical instruments with the unwanted sediment.

Environmental testing

Environmental materials such as water, soil and air can be filtered to provide pure samples for analysis, as well as isolating any contaminants that may be present in order to understand their presence.

Protein binding assays

A syringe filter can be used to separate free and bound protein fractions to determine their concentration, as the free proteins are separated from the proteins bound to other molecules during the filtration process.

Sample preparation

Filters can remove impurities and particulate matter that interfere with some analytical techniques, such as high-performance liquid chromatography (HPLC), gas chromatography (GC) and mass spectrometry (MS).

Solvent filtration

Syringe filters can help enable reliable results in a variety of applications by removing impurities from solvents. Some areas where this might be required include environmental analysis, pharmaceutical research and food testing.

Sterilization

To ensure sterile sample preparation, filters can remove fungi, bacteria and other microorganisms or contaminants from small volumes of liquids, making them safe for microbial analysis or cell culture work.

What types of syringe filters are available?

Syringe filters come in a variety of types, generally classified on the basis of their housing and membrane composition, filter diameter and pore size.

Housing composition

Syringe filter housing is typically made from polypropylene, polycarbonate, stainless steel or acrylic.

Polypropylene and acrylic housing is single-use, and must be disposed of along with the filter it houses. Polypropylene is the more versatile choice, as it is chemically resistant and appropriate for use with most solvents. If your application requires you to see the filtrate, acrylic housing could be the better choice as it is transparent to allow for visual inspection.

Polycarbonate and stainless steel housing offers a reusable alternative, where the housing can be sterilized and reused for a wide variety of applications. However, it is important to remember that the filter itself is NOT reusable, and must be disposed of after each use.

Membrane composition

The membrane of a syringe filter can be made from a range of materials, the most common being nylon, cellulose acetate (CA) polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethersulfone (PES) or borosilicate glass fiber.

Nylon is the most versatile option, as it is compatible with a wide range of aqueous and organic solvents and ideal for general laboratory filtration requirements.

CA filters are commonly used with aqueous solutions, biological fluids and proteinaceous samples, as well as aggressive organic solvents.

PTFE is often used for filtering air and gas samples, as well as aggressive organic solvents, acids and bases.

PVDF is resistant to most solvents, suitable for the filtration of aqueous and organic solvents as well as protein, enzyme and other biological material filtration.

PES offers high flow rates and low protein binding, making it suitable for samples containing biological material, in addition to organic and aqueous solutions.

Borosilicate glass fiber filters are equipped for particle-laden applications and viscous solutions, commonly used in environmental analysis and food testing.

Filter diameter

Syringe filters are commonly available in a variety of diameters, and the size required depends on the sample size and type of application being carried out. Diameters typically range from 4mm to 33mm, with smaller sample volumes requiring a smaller diameter and vice versa.

Pore size

The pore size of a filter dictates the size of contaminants that can or cannot be filtered through, typically measured in micrometers (µm). The most commonly used pore sizes range from 0.1µm to 5µm, but these offer considerably different results so it is important to choose the correct size.