2024-02-19
Filter Material-how to choose the appropriate filter material
A hydrophobic membrane, such as polytetrafluoroethylene (PTFE) will resist any aqueous sample, creating back pressure. Although it is sometimes possible to overcome this back pressure with additional force, there is a risk of membrane rupture and incomplete filtration.Should there be no alternative, pre-wetting the membrane with an alcohol can reduce this back-pressure effect.PTFE and other hydrophobic materials are well suited to organic samples and solvents, which result in no resistance or back pressure. However, some organic solvents can absorb into the membrane material, especially when in contact for long periods.This absorption makes the material swell, reducing pore size and affecting the performance of the filter. Some solvents might also chemically attack the material, releasing extractables into the filtrate. In rare cases, a solvent might partly or fully dissolve the membrane, resulting in breakthrough and potential contamination of the sample.Aqueous samples are unlikely to damage most membrane materials, particularly hydrophilic. However, pH is a significant factor in determining membrane compatibility.Strongly acidic or alkaline solvents might not immediately damage a membrane but can have an effect over time. As such, only highly inert membranes such as PTFE are suitable for high and low pH samples.