A separatory funnel, also known as a separation funnel, separating funnel, or colloquially sep funnel, is a piece of

laboratory glassware Laboratory glassware refers to a variety of equipment used in scientific work, and traditionally made of glass. Glass can be blown, bent, cut, molded, and formed into many sizes and shapes, and is therefore common in chemistry, biology, and anal ...

used in liquid-liquid extractions to separate (''partition'') the components of a mixture into two immiscible

solvent A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...

phases of different

densities Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek language, Greek letter Rho (letter), rho), although the Latin letter ''D'' ca ...

. Typically, one of the phases will be aqueous, and the other a

lipophilic Lipophilicity (from Greek λίπος "fat" and φίλος "friendly"), refers to the ability of a chemical compound to dissolve in fats, oils, lipids, and non-polar solvents such as hexane or toluene. Such non-polar solvents are themselves lipop ...

organic solvent A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for p ...

such as

ether In organic chemistry, ethers are a class of compounds that contain an ether group—an oxygen atom connected to two alkyl or aryl groups. They have the general formula , where R and R′ represent the alkyl or aryl groups. Ethers can again be c ...

MTBE Methyl ''tertiary''-butyl ether (MTBE), also known as methyl tert-butyl ether and ''tert''-butyl methyl ether, is an organic compound with a structural formula (CH3)3COCH3. MTBE is a volatile, flammable, and colorless liquid that is sparingly sol ...

dichloromethane Dichloromethane (DCM or methylene chloride, methylene bichloride) is an organochlorine compound with the formula . This colorless, volatile liquid with a chloroform-like, sweet odour is widely used as a solvent. Although it is not miscible with ...

chloroform Chloroform, or trichloromethane, is an organic compound with chemical formula, formula Carbon, CHydrogen, HChlorine, Cl3 and a common organic solvent. It is a colorless, strong-smelling, dense liquid produced on a large scale as a precursor to ...

, or

ethyl acetate Ethyl acetate ( systematically ethyl ethanoate, commonly abbreviated EtOAc, ETAC or EA) is the organic compound with the formula , simplified to . This colorless liquid has a characteristic sweet smell (similar to pear drops) and is used in glues ...

. All of these solvents form a clear delineation between the two liquids. The more dense liquid, typically the aqueous phase unless the organic phase is

halogenated In chemistry, halogenation is a chemical reaction that entails the introduction of one or more halogens into a compound. Halide-containing compounds are pervasive, making this type of transformation important, e.g. in the production of polyme ...

, sinks to the bottom of the funnel and can be drained out through a valve away from the less dense liquid, which remains in the separatory funnel.

Description

A separating funnel takes the shape of a cone with a hemispherical end. It has a stopper at the top and

stopcock A stopcock is a form of valve used to control the flow of a liquid or gas. The term is not precise and is applied to many different types of valve. The only consistent attribute is that the valve is designed to completely stop the flow when clo ...

(tap), at the bottom. Separating funnels used in laboratories are typically made from

borosilicate glass Borosilicate glass is a type of glass with silica and boron trioxide as the main glass-forming constituents. Borosilicate glasses are known for having very low coefficients of thermal expansion (≈3 × 10−6 K−1 at 20 °C), ma ...

and their stopcocks are made from glass or

PTFE Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer of tetrafluoroethylene that has numerous applications. It is one of the best-known and widely applied PFAS. The commonly known brand name of PTFE-based composition is Teflon by Chemour ...

. Typical sizes are between 30 mL and 3 L. In industrial chemistry they can be much larger and for much larger volumes

centrifuge A centrifuge is a device that uses centrifugal force to separate various components of a fluid. This is achieved by spinning the fluid at high speed within a container, thereby separating fluids of different densities (e.g. cream from milk) or ...

s are used. The sloping sides are designed to facilitate the identification of the layers. The stopcock-controlled outlet is designed to drain the liquid out of the funnel. On top of the funnel there is a standard taper joint which fits with a ground glass or Teflon stopper. To use a separating funnel, the two phases and the mixture to be separated in solution are added through the top with the stopcock at the bottom closed. The funnel is then closed and shaken gently by inverting the funnel multiple times; if the two solutions are mixed together too vigorously

emulsions An emulsion is a mixture of two or more liquids that are normally immiscible (unmixable or unblendable) owing to liquid-liquid phase separation. Emulsions are part of a more general class of two-phase systems of matter called colloids. Althoug ...

will form. The funnel is then inverted and the stopcock carefully opened to release excess

vapor pressure Vapor pressure (or vapour pressure in English-speaking countries other than the US; see spelling differences) or equilibrium vapor pressure is defined as the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases ...

. The separating funnel is set aside to allow for the complete separation of the phases. The top and the bottom stopcock are then opened and the lower phase is released by

gravitation In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stron ...

. The top must be opened while releasing the lower phase to allow pressure equalization between the inside of the funnel and the atmosphere. When the bottom layer has been removed, the stopcock is closed and the upper layer is poured out through the top into another container. Scheidetrichter zwei Phasen brauner Hintergrund

Scheidetrichter zwei Phasen brauner Hintergrund

Theory

The separating funnel relies on the concept of "like dissolves like", which describes the ability of polar solvents to dissolve polar solutes and non-polar solvents to dissolve non-polar solutes. When the separating funnel is agitated, each solute migrates to the solvent (also referred to as "phase") in which it is more soluble. The solvents normally do not form a unified solution together because they are immiscible. When the funnel is kept stationary after agitation, the liquids form distinct physical layers - lower density liquids will stay above higher density liquids. A mixture of solutes is thus separated into two physically separate solutions, each enriched in different solutes. The stopcock may be opened after the two phases separate to allow the bottom layer to escape the separator funnel. The top layer may be retained in the separating funnel for further extractions with additional batches of solvent or drained out into a separate vessel for other uses. If it is desired to retain the bottom layer in the separating funnel for further extractions, both layers are taken out separately, and then the former bottom layer is returned to the separating funnel. Each independent solution can then be extracted again with additional batches of solvent, used for other physical or chemical processes. If the goal was to separate a soluble material from mixture, the solution containing that desired product can sometimes simply be evaporated to leave behind the purified solute. For this reason, it is a practical benefit to use

volatile solvent A solvent (s) (from the Latin language, Latin ''wikt:solvo#Latin, solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a Solution (chemistry), solution. A solvent is usually a liquid but can also be a solid, a ...

s for extracting the desired material from the mixture.

Emulsions

One of the drawbacks of using a separating funnel is

emulsion An emulsion is a mixture of two or more liquids that are normally immiscible (unmixable or unblendable) owing to liquid-liquid phase separation. Emulsions are part of a more general class of two-phase systems of matter called colloids. Althoug ...

s can form easily, and can take a long time to separate once formed. They are often formed while liquids are being mixed in the separating funnel. This can occur when small droplets are suspended in an aqueous solution. If an emulsion is formed, one technique used to separate the liquids is to slowly swirl the solution in the separating funnel. If the emulsion is not separated by this process, a small amount of saturated saline solution is added ("

salting out Salting out (also known as salt-induced precipitation, salt fractionation, anti-solvent crystallization, precipitation crystallization, or drowning out) is a purification technique that utilizes the reduced solubility of certain molecules in a s ...

"). Research is being done on alternative, more efficient techniques, mostly utilizing stir bars (stirrer bars) to decrease or even eliminate the chance of emulsification, thus decreasing the amount of waiting time.

Safety concerns

The largest risk when using a separating funnel is that of pressure build-up. Pressure accumulates during mixing if a gas evolving reaction or physical change occurs. This problem can be easily handled by simply opening the stopper at the top of the funnel routinely while mixing. More standard procedure is to invert the separating funnel upside down, and open the stopcock to release the pressure, a step done repeatedly known as 'venting'. This should be done with the tip of the funnel pointed away from the body.Fessenden, J., Joan S. Fessenden, Patty Feist. Organic Laboratory Techniques, 3rd Edition, 2001. Pacific Grove, California: Brooks Cole Publishing, p. 59.

Gallery

File:Separatory funnel-tag.svg, File:Separatory funnel.jpg, The ether layer with a dissolved yellow compound is on top and an aqueous layer is at the bottom File:(09-04-26).1 - 07 (Large).JPG,

Apple An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple fruit tree, trees are agriculture, cultivated worldwide and are the most widely grown species in the genus ''Malus''. The tree originated in Central Asia, wh ...

banana A banana is an elongated, edible fruit – botanically a berry – produced by several kinds of large herbaceous flowering plants in the genus ''Musa''. In some countries, bananas used for cooking may be called "plantains", distinguis ...

carrot The carrot ('' Daucus carota'' subsp. ''sativus'') is a root vegetable, typically orange in color, though purple, black, red, white, and yellow cultivars exist, all of which are domesticated forms of the wild carrot, ''Daucus carota'', nat ...

, and

lettuce Lettuce (''Lactuca sativa'') is an annual plant of the family Asteraceae. It is most often grown as a leaf vegetable, but sometimes for its stem and seeds. Lettuce is most often used for salads, although it is also seen in other kinds of food, ...

extraction using

acetone Acetone (2-propanone or dimethyl ketone), is an organic compound with the formula . It is the simplest and smallest ketone (). It is a colorless, highly volatile and flammable liquid with a characteristic pungent odour. Acetone is miscib ...

, water, and

. Lower layer is the organic layer.

References