Am I using the right filter material and size for my filtration?

Selecting the right filter for your lab filtration will help to ensure you get the desired results. After considering whether you need vacuum or gravity filtration, you then need to select a suitable filter material and size. [caption id="attachment_9504" align="aligncenter" width="300"] With so many types and sizes of filter paper available, make sure you choose the right one for the task[/caption]

Filter Material

Filter papers and membranes can be broadly classified into 3 material types; Cellulose filter papers;  these are used for most general filtrations of down to 2.5µm. Exact pore sizes and flow rates vary with grade. A good choice for basic gravity filtrations to remove precipitates.   Glass microfiber filters; these are formed from borosilicate glass in microscopic fibres. The structure allows retention of much finer particles, down to around 0.7µm - though again this varies with the grade. Glass microfibre filters should only be used flat and should not be folded.  They can withstand high temperatures up to 500°C so are suitable for use where high temperature ignition or drying is needed - for example gravimetric analysis such as in suspended solids analysis.   Membrane filters; unlike the other 2 types of filters, these usually retain almost all particles they remove on the membrane surface. This makes them a good choice when you want to recover or analyse the removed particles after filtration. Available in a range of materials, membrane filters can allow retention of extremely small particles down to 0.02µm.  

Filtration Method

When choosing the filter material you need to consider chemical compatibility, pore size and your filtration method as the different filter types are suitable for different methods;

	Gravity	Vacuum	Pressure
Cellulose Filter Papers	Yes	Yes	Not usually used
Glass Microfiber	No	Yes	Yes
Membranes	No	Yes	Yes

Filtration Volume

In addition to the material and method, the amount you need to filter should be considered in selecting the size of filter (and corresponding funnel or other apparatus). This will make sure the filtration is efficient - retaining all the particles required but still giving a reasonable speed.

Volume (ml)	Filter Diameter (mm)
15	90
20	110
35	125
75	150
135	185
300	240

We have a Camlab Quick guide to filtration and the right filters to use. For more information about filter papers of all materials and types, follow the links above or contact us with your questions;