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The Schlenk line, sometimes referred to as vacuum gas manifold, is a chemistry apparatus widely used in air-free techniques.
The Schlenk line consists of a singular or dual glass manifold with several ports, usually 4-5. One manifold is connected to a source of purified inert gas, while the other is connected to a vacuum pump. The inert-gas line is vented through an oil/glycerol bubbler, while solvent vapors and gaseous reaction products are prevented from contaminating the vacuum pump by a liquid nitrogen or dry-ice/acetone cold trap. Glass or PTFE stopcocks/taps allow vacuum or inert gas to be selected without the need for placing the sample on a separate line.
How to operate a Schlenk line
To start a Schlenk line, follow the next steps:
- First, check the whole installation and make sure all the ground glass joints are properly greased, all tubing is intact.
- Attach the cold trap to the installation.
- Close all valves on both the vacuum and inert gas Schlenk line ports, as well as the ones between the cold trap.
- Start the pump and wait until the pressure in the first segment no longer decreases.
- Open the valve leading to the cold trap and wait until the pressure stops decreasing. You can also open the other valve to the vacuum Schlenk line port, but this is not necessary, as this will be done anyway when purging the installation from the air
- Fill a dewar with liquid nitrogen or some other cooling bath and immerse the cold trap in it.
- Open the main valve of the inert gas cylinder completely then gently open the secondary valve and adjust the gas bubbling flow to 1-2 bubbles per second or lower if you're not using the line immediately or a few bubbles per second when maintaining inert atmosphere inside an installation.
To create an inert atmosphere inside a glass installation or flask, do the following:
- Connect the glass installation; make sure all the jointed glassware is well greased and all the valves are closed shut.
- Connect the vacuum tube from the vacuum Schlenk line port to one of the valves of your installation.
- Secure the glassware parts with keck clips, to prevent them from popping out of their place when filling the installation with inert gas.
- Increase the inert gas flow to around 5 bubbles/sec.
- Make sure the valve accessing the inert gas is closed.
- Slowly open the valve corresponding to the vacuum tube and wait until all the air has been purged from the installation.
- Close the valve between the cold trap and the vacuum Schlenk line.
- Slowly open the inert gas valve and let the gas fill the installation; when the bubbler begins to bubble again, the installation is filled with inert gas.
- Close the inert gas valve and open the vacuum cold trap valve to remove the first batch of inert gas from the installation.
- Repeat the process 3-4 times
- Connect one of the inert gas tube from the Schlenk line port to the installation and open the valve.
- Close the stopcock from the installation connected to the vacuum, then the valve from the Schlenk vacuum line port, and lastly the inert gas valve from the vacuum line port which supplies inert gas to the port.
- Disconnect the vacuum tube from the installation.
- Reduce the inert gas flow to a few bubbles per second.
Safely turning off a Schlenk line requires the following steps:
- Turn off the vacuum pump.
- Quickly remove the liquid nitrogen dewar and place the cold trap on a cork stand.
- Immediately open the venting stopcock valve (the one between the vacuum pump and the first cold trap valve).
- Close the first valve.
- Quickly open the mid valve (between the trap and the Schlenk line).
- Open one or more of the vacuum Schlenk line valves.
- If your installation has a condenser, do not turn it on until you've removed all the air inside the set-up, to prevent water vapor from condensing inside it and ruin your system.
- It's recommended to have two gas valves on your installation.
- When closing the Schlenk valve, you must move quickly, to prevent a build-up of pressure in the trap from the dilation of condensed gasses which may cause an explosion.
Can be purchased from lab suppliers or online. A complete Schlenk system however (includes vacuum pump, inert gas cylinder, gas bubbler, good quality tubing, cold trap, cryogenic liquid, etc.) is quite pricey.
- Synthesis of organometallic compounds
- Vacuum dry wet compounds
Handling and safety
The main dangers associated with the use of a Schlenk line are the risks of an implosion or explosion.
Always check if the stopcocks are properly greased.