Schlenk Lines

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Cannula transfer

Moving solutions on a Schlenk line

A cannula transfer or addition allows one solution to be transferred to another Schlenk tube using a Schlenk line. There are various ways this can be achieved depending on the requirements of the reaction and personal preferences. The general principle is that a cannula is inserted into one solution, and the pressure in that flask is increased compared to the receiving flask, which results in the solution being transferred to the second flask.

Cannulae come in a variety of different forms. Historically cannulae were constructed from metals (typically stainless steel), but nowadays disposable plastic cannulae are more commonly used. A variety of needle gauges (diameters) are used which changes the rates of addition. Metal cannulae come in a variety of lengths, whereas plastic cannulae are cut to the desired length as required. Most cannulae feature two bevelled (sloped, pointed) ends, which enable them to be inserted through septa as required. However, plastic cannulae are not very sharp (even when cut with a bevelled end) so only try to insert them through a pre-pierced septum.

Cannula transfer

The method below details one approach for the transfer of a solution which has been prepared in a Schlenk tube into another solution in a second Schlenk tube using a disposable plastic cannula.

Obtain a length of disposable cannula tubing. The length required is generally about 2.5 times the length of the Schlenk tube. The cannula will need to be able to run from the bottom of one Schlenk tube, out the top, across in a loop and into the receiving Schlenk tube.
The ends of the cannula should be cut to have a sharp, bevelled end which will be needed to pierce through septa.
Insert each end of the cannula through an appropriate septum for each of the Schlenk tubes. The ends of the cannula need to be through the septa, but not so far that they would end up in the solutions in the Schlenk tubes.
Ensure both the receiving and donating Schlenk tubes are connected via the double oblique taps and side arm taps to the gas manifold.
Remove the stopper from the donating Schlenk tube and quickly insert the septum (which is now pierced with the cannula). There should be a gas flow from the manifold, through the Schlenk tube and out of the cannula (check you can feel the flow – the rate of gas flow through the oil bubbler should decrease or stop).
Allow the cannula to be purged with gas for a few moments to ensure that any air has been displaced.
Insert the other septum into the receiving flask, after removing the stopper/helmet. As both flasks are open to the gas manifold, there should be no net flow of gas through the cannula.
Close the side arm tap on the receiving Schlenk tube and insert a needle into its septum (next to the cannula). This should result in a flow of gas from the donor flask, via the cannula into the receiving flask, and exit via the needle.
Carefully push the end of the cannula into the donor solution and the solution may begin to transfer through the cannula into the receiving Schlenk tube.
The solution can be encouraged to transfer by partially closing the gas exit from the oil bubbler using a finger which will divert the gas flow through the next easiest route which should be the cannula to needle exit. Care should be taken to not build up too much pressure on the line.