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Figure 1
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The separatory funnel is used to perform simple extractions. The separatory funnel has three distinct parts: 1) the stopper (at the top), 2) the vessel itself, and 3) the stopcock (at the bottom) (Figure 1) When the separatory funnel is in use, it is generally positioned through a ring (of appropriate size) mounted to a sturdy ring stand. The solvents and solutions used in the extraction are added to the separatory funnel through the ground-glass joint at the top of the funnel. Solvents and solutions should be added to the funnel using a glass funnel to avoid contaminating the joint. (Contaminants will prevent a tight seal from forming). The stopcock at the bottom of the funnel must be in the closed position (perpendicular to the stem or "drain"). When two immisible solvents (solvents insoluble in each other) are placed in the separatory funnel, two distinct layers should be visible. (Figure 2). |
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Figure 2 |
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Figure 3 |
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The
solvents/solutions are typically an organic (lipohilic,
non-polar) phase and an aqueous (hydrophilic, polar)
phase. These phases are not misible. Shaking the
separatory funnel allows the two solvents to mix and
provides the opportunity for components dissolved in one of
the solvents to be transferred to the other solvent.
Proper technique for shaking the separatory funnel is
illustrated in Figure 2. The stopper should be placed
in the top of the funnel before removing it from the ring
and the stopcock should be in the closed position. The
stopper must be held firmly in place by holding it with the
index finger or palm of the hand. The stem (out spout)
must be directed into the back of the hood and the funnel
should be positioned with the stem pointed upward at an
angle of ~ 45degrees. Mixing occurs by gently shaking
the funnel for ~10-30 seconds, after which the stopcock
should be opened, with the funnel tilted upward, to
vent any gases generated by the shaking process. After
venting the gases, the stopcock should be closed and the
funnel returned to the ring. The two layers are separated after shaking by draining the lower layer from the bottom of the separatory funnel. The stopper must be removed from the funnel prior to draining. The bottom layer is drained into a clean, labeled beaker or flask by opening the stopcock and closing it quickly when the interface region reaches the bottom of the funnel. A second beaker or flask is used to collect the remaining layer in the funnel. |
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Figure 4
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Addition of small quantities (10-100mg) of salt (NaCl or equivalent) to the funnel, followed by gently shaking or swirling. Adding too much salt to the separatory funnel may clog the stopcock, so add sparingly. |
Addition of one or the other of solvents used in the extraction. |
Addition of ethanol which has solubility in both aqueous and organic solvents. |
Addition of small quantities of dilute aqueous acid or base (1-2ml). Note that some components may react with acid or base so use this method as a last resort if the components are acid or base sensitive. |
Table 1: Techniques for breaking emulsions
In addition to emulsions, separation of the two solvents is often complicated by a "third layer" or the interface between the two solvents. A large interface is likely just a small emulsion and can be handled using the techniques listed in table 1. Usually the best technique to use for an intereface problem is to add on or the other of the two solvents used in the extraction. The interface contains both solvents and likely all the components of the mixture. If the interface is collected with a specific layer, that layer will be contaminated with all components of the mixture. To ensure a completely clean separation of the two layers, it is sometimes nessary to collect the interface in a third beaker.