How to Choose a Filter
What Should You Consider?
Most filters look alike, but they have significant technical differences. These differences are meant to ensure that the filter is optimized to support the analysis being performed. The sheer number of choices presents a risk of choosing a filter that is not fit for the purpose. When a laboratory's reputation depends on reliable, consistent, and repeatable analysis, choosing the correct filter for the job is critical. There are three main considerations when identifying which filter is best suited to the application. These factors influence the effectiveness and speed of filtration.
Filter Characteristics
Particle Retention
Particle Retention
Particle Retention
- The particle retention of a filter describes the size of a particle that will be retained and is often expressed in micrometers (µ or microns). For cellulose and glass microfiber papers, it is expressed as a "nominal retention rating", and quoted at 98% efficiency to allow for secondary filtration effects. For membrane filters with define
- The particle retention of a filter describes the size of a particle that will be retained and is often expressed in micrometers (µ or microns). For cellulose and glass microfiber papers, it is expressed as a "nominal retention rating", and quoted at 98% efficiency to allow for secondary filtration effects. For membrane filters with defined pore sizes, it is an absolute retention rating. The lower the particle retention value of a filter, the smaller the particles that will be retained.
- Make sure that you know the particle size of the compound you're looking to filter from solution, as well as the compound size you want to let pass through the filter. Together with COBEAL select a paper with a slightly smaller retention rating than the particle to remove. For example, if you need to remove a 5.8µ diameter particle from a fluid, consider a filter with a 5µ retention rating.
Loading Capacity
Particle Retention
Particle Retention
- The loading capacity of a filter is related to its ability to load particulates into a fibrous matrix. It is common to want a high loading capacity, but there are trade-offs.
- Filters with the highest loading capacities are chemically treated and are more expensive than their untreated counterparts. Treatment might also interfere with anal
- The loading capacity of a filter is related to its ability to load particulates into a fibrous matrix. It is common to want a high loading capacity, but there are trade-offs.
- Filters with the highest loading capacities are chemically treated and are more expensive than their untreated counterparts. Treatment might also interfere with analysis. This can happen either through chemical interaction with the sample or by increasing the time to results due to a slower flow rate than that of an untreated filter.
- By knowing the weight of filtrate that you want to retain on the filter, together with COBEAL you can choose a filter that will safely accommodate your needs without the downsides of a filter than is more complex than is needed.
Fluid Flow Rate
Particle Retention
Fluid Flow Rate
- The flow rate describes the speed at which a fluid flows through the filter. In practice, this is dependent on several factors that will often be specific to the solid/fluid being filtered. But, for comparison purposes, a typical fluid flow rate is measured and provided for each grade under gravity and normalized to a certain diameter.
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- The flow rate describes the speed at which a fluid flows through the filter. In practice, this is dependent on several factors that will often be specific to the solid/fluid being filtered. But, for comparison purposes, a typical fluid flow rate is measured and provided for each grade under gravity and normalized to a certain diameter.
- After you know the retention rate and loading capacity of the filter you're looking for, COBEAL can help you compare your options to understand roughly which filters support higher flow rates and which support lower ones.
- Ultimately, your decision will come down to the requirements of your work - do you have a sample that needs to be filtered immediately, or can the sample be left alone to be filtered in due time? Is a specified fluid flow rate required and maintained by either positive or negative pressure? If so, COBEAL will help you choose a filter with a rating that can support these requirements without tearing.