Filtration is a technique used to separate a solid from a liquid. The solid is separated from the liquid phase by passing the mixture over a filtering media. Filtering media is characterized by being chemically inert to the mixture, and having small pathways for the liquid to pass through, but these pathways should be smaller than the soiid particle size. Filtering media can be prepared using paper, fritted-glass, or any porous material.
The mixture can be forced through the filter by either gravity or reduced pressure on one side of the filter (by creating a vacuum). It is possible to separate a solid from a liquid by either technique, however there are advantages to each technique.
Gravity Filtration is recommended when:
- the mixture is hot (above room temperature)
- the liquid is saturated with one or more reagents
- the solvent is very volatile (chloroform, alcohols, ethers).
Vacuum Filtration is recommended when:
- the conditions where gravity filtration is recommended are NOT present
- a quick separation is required