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.