Lab Separation: 5 Tips for Choosing Your Ideal System

Filtration is a critical technique in the laboratory. From reagent sterilization and basic research applications to clinical and environmental testing, filtration is one of the fundamental steps in preparing samples for downstream analysis. There are so many factors to consider when choosing a filtration system, from material compatibility to pore size. We’re breaking down the top five in this blog.

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1. Filter material
 

• Depth filters have a thick layer of porous material, such as cellulose or glass fiber, and are typically used for large-volume and low-pressure applications. They trap particles on the surface of the filter and within its structure.
• Track-etched filters are manufactured from high-grade polycarbonate film with a broad range of precise pore sizes for accurate separation and retention of particles retaining no particles in the structure of the filter.
• Microfiltration membranes are made from various polymers and use a thin, microporous membrane to separate or retain particles on the membrane surface due to its sponge-like structure. 
• Ultrafiltration membranes are semi-permeable membranes designed to retain macromolecules when a driving force like pressure is applied. 
• Chromatography membranes are not filters per se, but are made in a similar way to microfiltration membranes. They are highly specialized stationary phase matrices that have been functionalized with ion exchange or affinity ligands for use in purifying and polishing biomolecules based on their chemical and physical properties.

2. Filter pore size
 

Pore size determines the size range of particles that can pass through or be retained by a filter. The exact pore size needed for a given application will depend on the specific sample, required purity and yield. In some cases, you may need multiple filtration steps, using different pore size filters to get the desired result.
 

• Depth filtration (0.7–100 µm) is used for removing visible and smaller particles or for removing cells after harvesting a bioreactor. 
• Microfiltration (0.1–10 μm) can retain particles like bacteria, yeast, and large cells from the surrounding liquid, and are commonly used for clarification, sterilization, and removal of contaminants.
• Ultrafiltration (1–100 nm) membranes retain macromolecules such as such as proteins, nucleic acids, viruses, and nanoparticles from liquid samples. These filters are used for concentration, buffer exchange and desalting of biomolecules and may also be used for removing proteins.
• Chromatography (up to several hundred nanometers) membranes have a macroporous structure, enabling the purification of not only proteins and nucleic acids, but even larger protein complexes and viruses.  
• Reverse osmosis (less than 1 nanometer) is used to remove salts and other small molecules from water and other liquids, such as for preparation of ultra-pure water.

3. Material compatibility
  

To get the best yield and purity, the filter material should be chemically and physically compatible with the content and composition of the sample being filtered. For example, some filter housings are more chemically resistant than others. In addition, some filters may be considered “sticky” for specific proteins; this means proteins will adsorb to the membrane, reducing the final yield. Finally, a filter material that is not compatible with the process conditions, such as operating temperature, pressure, and pH, may shrink, expand or deform. This may result in leaks or changes in the filter pore size.
 

4. Flow rate
 

The flow rate is how fast a liquid or gas passes through a filter. It depends on various factors, including the filter material, pore size, surface area available for filtration, sample viscosity and temperature, and whether a prefiltration step is used. While a higher flow rate can speed things up, it can also retain less of the material you want, which impacts the purity and yield of your final product. To get the best result, it is important to find the optimal balance between flow rate and retention.

5. Filter product

Depending on the application, you may need different types of filter products. For example, syringe filters are small, disposable filters typically used for lab-scale filtration for sample preparation, sterilization, and clarification of aqueous solutions, solvents, and other liquids. Clarification filters are designed to remove larger particles and impurities from liquids and can be used in various workflows, including cell culture. In-line filters are another type of filter product that are installed directly into a fluid or gas line to remove contaminants and particulate matter as the fluid flows through the system.

Sartorius is a trusted provider of reliable laboratory filtration and purification products for a wide range of applications, including basic research, drug discovery, analytics, and diagnostic testing. Discover our depth filters, microporous membranes, syringe filters, clarification filters, in-line filters, and other products.