Introduction to Microscale Filtration

Microscale filtration carries out the same process as other types of filtration, resulting in the separation of a residue and filtrate from a suspension. Microfiltration allows this to be undertaken on a small scale. Usually microfiltration is used to access the filtrate, with residue isolation being impractical for most of these microscale techniques.

Pipette filtration

Sometimes the amount of material requiring filtration is very small (only a few mL) and a using a pipette and cotton wool to form a small filter is often an effective filtration method. Pipette filters can also be used with other materials to enable small scale cleanup, for example using silica gel or to remove water using magnesium sulfate. Probably the most common use of a cotton wool pipette filter is for the filtration of NMR samples.

1. Take a Pasteur pipette and insert a small ball of cotton wool into the top of the pipette and use a brass rod to push the cotton wool into the narrowing of the neck. There is a compromise between ensuring the cotton wool is in place and compacting it too much that filtration is slow.

2. If filtration though another material is required, use the pipette to scoop up the solid material (for example magnesium sulfate or silica) from the reagent pot and tap it to remove any excess from the sides. Wipe the outside of the pipette clean from any residual material.

3. Clamp the pipette filter above the receiving vessel. This may be a small beaker/funnel/volumetric flask, a sample vial or an NMR tube depending on requirements.

4. Add the solution to be filtered to the top of the pipette and allow it to pass through the filter. For cotton wool, gravity is usually sufficient for the liquid to filter. Where another material is present, the use of a pipette bulb may be required to 'force' the solution through the material. Continue to add solution and allow it to pass through the filter until complete.

5. To ensure all compound has eluted, it may be nescessary to wash through the filter with additional solvent.

6. Used pipette filters should be disposed of appropriately.

Video

Syringe filtration