How to clean the sinter of a Büchner flask?

Are the sinters of frits of your funnels and glassware blocked? Is the flow-through extremely slow or retarded?

Here's a simple method to clean those blocked sinters.

The first thing to note is that the method uses highly corrosive acids and generates a very strong oxidizing agent. For these reason make sure the following are strictly followed:

• Wear a closed lab coat
• Wear safety glasses of face shield
• Wear suitable gloves
• Perform in a fume hood with the sash closed
• Ensure all excess organic material is washed from the sinter before cleaning

So how do you clean the frit/ sinter? The "trick" is Piranha solution, also known as piranha etch.  It is a mixture of sulfuric acid (H₂SO₄) and hydrogen peroxide (H₂O₂). This strong oxidizing solution will remove most organic matter and also make most surfaces highly hydrophilic by adding hydroxyl groups.

A Simple Method

1. In a fume hood attach Büchner sintered funnel to be cleaned to a vacuum flask, ensure that it is secure. Attach vacuum to flask.

   NOTE: If you think acetone or another organic solvent is still present then wash with copious amounts of water.

2. Add 50ml sulfuric acid, or enough to cover the entire surface of the Büchner funnel sinter.

3. Carefully add 15ml 30% hydrogen peroxide, or 1/3 the volume of sulfuric acid used, to the Büchner funnel and stand back!

4. Let the reaction proceed for about a minute and then apply a quick vacuum (just enough to pull the solution through the sinter into the flask and the sinter is dry.)

5. Monitor the reaction. DO NOT LEAVE UNATTENDED. Once the reaction has subsided allow reaction mix to cool in the flask overnight.  

6. Wash flask, sinter, funnel and all equipment used thoroughly in water.  Sinter should now be clean with optimal flow conditions.

For disposal of the used Piranha solution:

• Do not leave unattended if still hot
• Allow to fully cool overnight as this allows all oxygen gas to dissipate
• Do not store in a closed container
• Do NOT dispose of in a waste solvent bottle
• Check with your institutes disposal regulations as some require collection as hazardous waste, others allow neutralization and disposal with copious volumes of water.