7. FAQ's and Knowledgebase / Filtration

Filtration and filter paper types – what’s the difference between filters?

When looking for filters there are a lot of different options available to suit different applications. It is important to ensure you choose the best type for your work, but what do the different terms mean?

Paper or Cellulose Filters – these are manufactured from cellulose fibres and are used for general filtration. The particle retention level can go down to 2.5 µm. This type of filter paper is used for basic gravity filtration using a glass or plastic filtration funnel – for this the filter paper must be folded. Pre-folded versions are available in some grades.

Glass Microfibre Filters –  these are manufactured from glass microfibres allowing the particle retention to go down to the submicron range. They can also withstand higer temperatures (up to around 550°C) so can be used in gravimetric analyses where ignition is required. Glass microfibre filters must be used flat, they cannot be folded like paper filters – they may be used with a Buchner funnel or a 3-piece filter unit.

Membrane Filters – these retain particles on the membrane surface. Retention can go down as low as 0.02 µm, meaning they are commonly used in microbiological and air pollution applications.

Pore Size – this is the nominal size of the pores in the filter, particles larger than this size will be retained, while particles smaller than this size may go through the filter.

Ashless / Low Ash Content –  Quantitative cellulose filter papers can be described as ashless or low ash grade, this is determined by igniting a cellulose filter at 900°C in air.  Ashless filter papers are used in critical analytical applications, for example in gravimetric analyses.

Quantitative Filter Papers – these are used for gravimetric analyses or filtrations where the preipitate is to be recovered, for example from a Buchner funnel filtration under vacuum.

Qualitative Filter Papers – these are used in qualitative techniques to identify materials. They do not offer the same level of precipitate recovery as quantitative filter papers.

Camlab offer a wide range of filters to suit all applications – if you are unsure of what type is best for your application just contact us to discuss it further and we will be happy to advise.

8 thoughts on “Filtration and filter paper types – what’s the difference between filters?

  1. Our clinic is evaluating underarm sweating by the collection of sweat over a 5 minute period with the placement of filter paper in the axilla with arm down. The sample is then weighed on a analytical balance. What is the best filter paper for this application?

    1. Hi there,
      The filters we have discussed here are small paper filters for removing particulates from liquid samples. If you are welding and producing fumes you will need some kind of extraction system like a fume hood or extraction fan, as well as suitable PPE.
      Your health and safety representative should be able to help in choosing the right equipment after completing a risk assessment.

      Kind regards, Camlab Support Team

  2. Hi camlab, we are looking for filter paper that will best suit in our research. We are going to filter the powderized leaves immersed in Ethanol on a glass to get its extract.

  3. we are going to filter a potassium permanganate solution but we dont have asbestos filter, is it okay if we use the whatman quantitative filter paper no.41?

  4. We are looking for good filtration process by using perfect filter paper. Last time, we used membrane filters for Lipomyces starkeyi and Rhodosporidium toruloides. In the filtrate, we saw it looks turbid. Some cells of these species went through this membrane filters. In this case, which type of filter paper should we use in our experiment?

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