- Filter Paper (qualitative or quantitative)
- Büchner Funnel
- Filter Adapter (or rubber stopper or bung)
- Filtering Flask (pictured is an Erlenmeyer-style flask)
- Vacuum Hose
- Vacuum Pump, not shown.
Qualitative filter paper has larger pores and filters faster than quantitative paper. The larger pores allow more material to get through.
Quantitative paper is the opposite: its smaller pores filter more finely, and the expense of filtration speed. Which one is the right choice depends on the scenario.
With these basic products in place, you are now able to start the filtering process.
How does vacuum filtration work?
Once you have the proper equipment set up (more or less as pictured above), there are a few steps to take to ensure the process goes smoothly:
- Insert the filter paper into the Büchner funnel. It should be as close to an exact fit as possible. If the paper’s diameter is too big, simply cut it to the appropriate shape using regular scissors.
- Insert the rubber stopper into your filtering flask. The stopper should have a hole cut out of the center, so that the funnel can fit snugly and securely inside without touching the walls of the glass.
- Place the funnel inside the stopper. Or, put them together first and connect them to the flask as one unit.
- Connect the tubing to the side spout. Connect the other end of the hose to your vacuum pump.
- Thoroughly moisten the filter paper with the same solvent or liquid that forms the basis of the solution you are filtering. This step is critical, because it creates an air-tight seal between the filter paper and the funnel, preventing any unwanted contaminants from sliding through.
- When everything is tightly connected, turn on your pump.
- Pour the solution you wish to filter into the top of the funnel.
- Solids will be collected on top of the filter paper, and the filtered solvent will be captured in the filtering flask.
- Repeat as necessary until the desired purity is achieved.
Suction creates a pressure differential.
As the directional arrow in the tubing shows, the vacuum is pulled through the tube, away from the Büchner Flask. This pulls the liquid or solvent down through the funnel at the top at a faster rate than gravity alone could.
The pressure of the suction also adheres the filter paper to the funnel on which it is resting, creating a tight seal that doesn’t allow particulate matter to slip through. This same suction presses the funnel into the filter adapter, creating a tight seal that doesn’t allow particulate matter to sneak through.
As you can see, the process itself is fairly straightforward, and it’s highly effective!
Critical for effective separation.
Vacuum filtration works particularly well when separating fats or lipids, which are stuck or suspended in a solution and need to be removed. For example, the fats or lipids trapped in plant materials can be caught by well-chosen filter media.
Depending on what you are filtering, the residue left on the filter paper can either be discarded, reused, or processed again.
A filter will also catch other solid particulates, such as catalysts, salts, impurities and any other unwanted solids.
Control multiple vacuum flows with a single pump.
Your valuable pumps are often at a premium in the laboratory. With our vacuum manifold kit, you can precisely control the amount of vacuum going out to multiple systems, all run by the same pump!
Because the glass and products used will be subjected to pressure in vacuum filtration, make sure that glass used can withstand this pressure. We recommend, high quality, borosilicate glass for the task.
The filter paper itself will reduce system flow rate, therefore suction filtration or vacuum filtration is performed to increase flow rate and reduce time. However, too strong of a vacuum can damage the paper or suck it in too strongly.
Depending on the substance you are trying to filter, a vacuum trap may be needed to reduce the chance of vapors reaching the vacuum pump, which could potentially damage it.