Schlenk filtration

One very important technique used in this course is a filtration under inert gas. The basic setup consists of a Schlenk flask, a Schlenk frit and a cap. The connection to the vacuum line should be at the top part of the Schlenk frit to remove the contaminants (e.g. water, air). After the drying process, a plastic clip is attached at the connection between the flask and frit.

In order to filter, first remove the cap (under a positive pressure in your inert gas line) and invert the setup. The flask with the solution to be filtered has to be at ambient pressure as well. Then, open the flask and join the two parts of the setup. Attach another plastic clip at the joints to hold them together. Slowly invert the assembly, making sure that the solution does get into the inert gas line. (Sometimes it is better to close them to prevent this from happening. Be careful, a significant pressure can build up then! It might be a good idea to hold the setup together with your hands if you filter low boiling solvents.) After a short time, open the stopcock of the receiving flask to perform a pressure exchange. In some cases, you will have to apply a slight vacuum to increase the speed of the filtration. But be aware that low boiling solvents or hot solvents evaporate at the frit leaving behind a solid material, which makes it even harder to filter. If you have a very fine precipitate e.g. NaCl, LiCl, try to avoid pouring it on the fritted part in the beginning. It will clog it up and the filtration will take much longer than your lab period.