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Schlenk: Addition of Liquids

In this video it is explained how to add liquids to a flask under inert-gas atmosphere. Described is how to use a dropping funnel and a perfusor.

To add a liquid to an inert-gas flask, two methods can be used. The Dropping funnel or a perfusor.

Dropping funnel
It's best to install the funnel along with rest of the set up, but not necessary. It can be schlenked separately and added under counter flow later. The Funnel is greased, stuck into the joint of the flask und turned to provide full sealing. If the joints have different sizes, it is necessary to use a Reduzierstück. The valves of the used flasks are set to inert gas and the plugs are substituted with septa. To do this, the plug of a flask is removed and a septum is put into the opening, slightly lit to let remaining oxygen flow out and put in the opening again. After doing this three times the septum is everted around the opening. Now a syringe of proper volume is selected. To get rid of the oxygen in the syringe, the septum is punctured with the syringe and inert gas is taken in. Afterwards the syringe is emptied to the ambient atmosphere. This is repeated to times. Now the desired amount of liquid can be taken into the syringe and injected into the dropping funnel. The septa are substituted by plugs again to provide sealing. To adjust the dropping speed the valves is opened carefully. The speed can only be adjusted roughly and it decreases with descending filling height.

Perfusor
Preparational steps are equal to those of the funnel, only the filled syringe is put into the persfusor and addition is controlled mechanically. With this method it is possible to add a defined amount of liquid over a defined amount of time. If a smaller syringe than it is possible to fit into the perfusor is used, an adapter syringe is needed. It's important to take the different sizes of the syringes into account when entering the addition volume. A smaller one contains less liquid, so the scales have to be compared. If, e.g. 30 mL of a small syringe are 10 mL on the scale of that of the perfusor, 10 mL must be entered to add 30 mL.