Separatory Funnel Extraction Procedure

1. Inspect your separatory funnel.

The organic chem teaching labs have acquired several different types of sep funnels over the past years, with different types of stopcocks and stoppers, as illustrated in the photo below. The Teflon stopcocks work better than the ground glass stopcock; if you have a sep funnel with a ground glass stopcock, you may exchange for a Teflon style.

The sep funnel on the left is a 60 mL size, the others are 125 mL. The organic chem teaching labs are downscaling slowly to this smaller size.
There are two different styles of stopper, too. Some students swear by the plastic style, some by the ground glass style. The disadvantage of the ground glass style is that it can lodge permanently in the sep funnel if it is not removed and stored separately after use. Whichever style you have, make sure that the stopper fits snugly in the top of the flask.

The Teflon-style stopcocks will leak unless they are properly assembled. The proper way to put them together is illustrated in the page linked to below:

2. Support the separatory funnel in a ring on a ringstand.

The rings are located on the back shelves and they come in many sizes. Test to make sure that you haven’t chosen too large a ring before setting the funnel in it. You can add pieces of cut tygon tubing to the ring to cushion the funnel.

Make sure the stopcock of the separatory funnel is closed!

3. Add the liquid to the separatory funnel.

Place a stemmed funnel in the neck of the separatory funnel. Add the liquid to be extracted, then add the extraction solvent. The total volume in the separatory funnel should not be greater than three-quarters of the funnel volume. Insert the stopper in the neck of the separatory funnel.

pour in liquid to be extracted . . . pour in the solvent . . . add a stopper

4. Shake the separatory funnel.

Pick up the separatory funnel with the stopper in place and the stopcock closed, and rock it once gently. Then, point the stem up and slowly open the stopcock to release excess pressure. Close the stopcock. Repeat this procedure until only a small amount of pressure is released when it is vented.

Now, shake the funnel vigorously for a few seconds. Release the pressure, then again shake vigorously. About 30 sec total vigorous shaking is usually sufficient to allow solutes to come to equilibrium between the two solvents.

Vent frequently to prevent pressure buildup, which can cause the stopcock and perhaps hazardous chemicals from blowing out. Take special care when washing acidic solutions with bicarbonate or carbonate since this produces a large volume of CO2 gas.

5. Separating the layers.

Let the funnel rest undisturbed until the layers are clearly separated. While waiting, remove the stopper and place a beaker or flask under the sep funnel.
Carefully open the stopcock and allow the lower layer to drain into the flask. Drain just to the point that the upper liquid barely reaches the stopcock. If the upper layer is to be removed from the funnel, remove it by pouring it out of the top of the funnel.

6. Perform multiple extractions as necessary.

Often you will need to do repeat extractions with fresh solvent. You can leave the upper layer in the separatory funnel if this layer contains the compound of interest. If the compound of interest is in the lower layer, the upper layer must be removed from the separatory funnel and replaced with the drained-off lower layer, to which fresh solvent is then added.

Yes, it can be confusing! Plus, the beginning student often does not know in which layer resides the compound of interest. The best advice: Always save all layers until the experiment is completely finished!

7. Store your separatory funnel with the cap (stopper) separate from the funnel!

If you do not store the cap separately, it can become irreversibly attached to the sep funnel. This is a constant problem in the organic chem teaching labs: a student comes to the stockroom with a cap lodged in the sep funnel. Yes, there are ways to remove the stopper. Sometimes. But in about 10% of the cases, while trying to remove a stubborn stopper, the separatory funnel is broken. Separatory funnels cost $30. So, simply because a student doesn't remove the stopper before storage, a $30 piece of glassware is ruined.

Please, remove the stopper before storage!!