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Cannula transfer or cannulation is a subset of air-free techniques used with a Schlenk line, in transferring liquid or solution samples between reaction vessels via cannulae, avoiding atmospheric contamination.
Cannula transfer can only be used to transfer liquids or solutions. An inert tubing, made of chemically resistant PE or PTFE is used as cannula.
There are two methods of transfer:
- Vacuum or negative pressure: Relies on creating a low pressure in the receiving flask.
- Pressure or positive pressure: High pressure is created in the transferring flask. This method is more commonly used, as it's safer;
How cannula transfer works
- You will need two flasks, preferably round-bottom flasks with side arm(s) or one sound bottom flask and a Schlenk flask;
- Check to see if the stopcocks are well greased and the grease does not clog the stopcock orifices;
- Cap your flasks using septums;
- Turn on the entire Schlenk system unless you already have;
- Take the cannula and insert it in the transferring flask through the septum;
- Connect the said flask to the Schlenk line;
- Purge the cannula with inert gas, make sure the cannula-septum hole is tight, to prevent gas from leaking;
- Add a syringe needle in the rubber septum from the receiving flask, while also connecting the flask to the Schlenk line, that way, a greater flow of inert gas will maintain the inert atmosphere from the receiving flask much better.
- Insert the other end of the cannula in the receiving flask;
- After a final check, push the end of the cannula tube in the first flask until it reaches the bottom of the flask with the liquid;
- Carefully open the inert gas line to inject gas in the transferring flask;
- As the pressure builds up, the liquid will be pushed through the cannula in the receiving flask;
- After all the liquid has been transferred, remove the cannula from the receiving flask, then from the transferring flask;
- Close the stopcock of the receiving flask;
- Another method is to open the gas stopcock of the receiving flask if you don't want to use a needle, however, this is not recommended;
- Quickly rinse the cannula with a solvent, to prevent any solids from forming in the tube and clogging it.