What is a Separating Funnel? Uses and How It Works

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Laboratory Glassware Guide · 6 min read

The separating funnel is one of the most important pieces of equipment in organic chemistry, extraction science and environmental analysis. Its distinctive pear or conical shape, glass stopcock and ground glass stopper make it instantly recognisable in any chemistry laboratory. Yet understanding exactly how it works, when to use it, and how to operate it correctly is essential for anyone working with immiscible liquids.

At LabFriend, we supply separating funnels from trusted manufacturers including ISOLAB, Thermo Nalgene and Lenz Laborglas. This guide covers everything you need to know, from the underlying science to step-by-step use and how to choose the right funnel for your application.

This guide covers

→ What a separating funnel is and how it works
→ The science behind liquid-liquid extraction
→ Step-by-step guide to using one safely and correctly
→ Types available, how to choose, and where to buy

What Is a Separating Funnel?

A separating funnel, also known as a separatory funnel or decanting funnel, is a piece of laboratory glassware used to separate two immiscible liquids, meaning liquids that do not dissolve into each other. The most common example is separating an organic solvent layer from an aqueous (water-based) layer during a liquid-liquid extraction procedure.

According to Wikipedia, separating funnels are typically made from borosilicate glass with stopcocks made from glass or PTFE, and come in sizes ranging from 30 mL to 3 L. They are essential tools in organic chemistry, pharmaceutical research, environmental testing and analytical laboratories worldwide.

Did you know? The separating funnel works on a fundamental chemistry principle: "like dissolves like." Polar compounds migrate into polar solvents (usually water), while non-polar compounds migrate into non-polar solvents (usually organic). This selective partitioning is the basis of liquid-liquid extraction, one of the most widely used separation techniques in chemistry. (Wikipedia)

Parts of a Separating Funnel

Funnel Body

The main vessel that holds the liquid mixture. Typically pear-shaped (Squibb) or conical, with sloping sides designed to make it easy to identify and observe the two distinct liquid layers during separation.

Stopcock

Located at the bottom of the funnel. Controls the outflow of liquid, allowing the lower layer to be drained precisely into a receiving vessel. Made from glass or PTFE. PTFE stopcocks are preferred as they do not require lubrication and resist most solvents.

Stopper / Top Cap

Seals the top of the funnel during shaking to prevent spillage. Made from glass, polyethylene or PTFE. The stopper must be removed or slightly vented when releasing pressure during use.

Ground Glass Joints (NS)

Standard taper (NS) ground glass joints at the neck allow the funnel to connect with stoppers and be used within larger glassware setups. Common sizes are NS 19/26 and NS 29/32 depending on funnel capacity.

How a Separating Funnel Works

The separating funnel exploits two fundamental physical properties of liquids: immiscibility and density differences. When two immiscible liquids are placed together in the funnel and shaken gently, solutes migrate between the two liquid phases according to their relative solubility in each. Once shaking stops and the mixture is allowed to settle, the two liquids separate into distinct layers, with the denser liquid sinking to the bottom and the lighter liquid rising to the top.

The stopcock at the bottom is then opened carefully to drain the lower layer into a receiving flask, leaving the upper layer inside the funnel. This process can be repeated multiple times with fresh solvent to improve extraction efficiency, a technique known as multiple extractions.

The Science Behind It

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Immiscibility

The two solvents do not mix. Water and most organic solvents (ether, ethyl acetate, dichloromethane) are immiscible.

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Density Difference

The denser liquid sinks to form the bottom layer. Water (1.0 g/mL) is denser than most organic solvents like ethyl acetate (0.9 g/mL), but less dense than dichloromethane (1.33 g/mL).

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Partitioning

Solutes distribute between the two phases according to their partition coefficient. Multiple extractions increase the total yield of the desired compound.

Common Laboratory Uses

1. Liquid-Liquid Extraction

The primary use of a separating funnel. A target compound is transferred from one solvent phase into another by exploiting differences in solubility. For example, an organic product dissolved in an aqueous reaction mixture is extracted into an organic solvent such as ethyl acetate or diethyl ether, then the layers are separated by draining. This is a fundamental technique in organic synthesis and natural product isolation.

2. Purification of Organic Compounds

After a chemical reaction, the crude product is often contaminated with inorganic salts, acids, bases or water-soluble impurities. Washing the organic layer with aqueous solutions (sodium bicarbonate to remove acids, dilute hydrochloric acid to remove amines, brine to remove water) in a separating funnel removes these impurities while retaining the desired product in the organic phase.

3. Pharmaceutical and Active Ingredient Isolation

In pharmaceutical manufacturing and research, separating funnels are used to isolate active pharmaceutical ingredients (APIs) from reaction mixtures, remove residual solvents and separate impurities from purified products. The ability to perform controlled, multi-step extractions makes the separating funnel indispensable in drug synthesis workflows.

4. Environmental and Water Analysis

Separating funnels are used to extract organic pollutants, pesticide residues or trace contaminants from water and environmental samples into an organic phase for subsequent analysis by GC, HPLC or spectroscopy. This is a standard sample preparation step in environmental testing laboratories following EPA and ISO method requirements.

5. Natural Product Extraction

Plant and animal extracts often contain a complex mixture of compounds. Separating funnels allow researchers to selectively extract target compounds such as alkaloids, flavonoids, essential oils or lipids by choosing appropriate solvent pairs, enabling systematic fractionation of natural product mixtures for biological or chemical evaluation.

How to Use a Separating Funnel Step by Step

Correct technique is essential when using a separating funnel, both for safety and to achieve a clean separation. Follow these steps for reliable results.

Step 1: Set up and check

Clamp the separating funnel securely on a retort stand with the stopcock closed. Check that the stopcock turns smoothly and is fully closed. For glass stopcocks, apply a thin film of stopcock grease. PTFE stopcocks require no lubrication.

Step 2: Add the liquids

Pour the mixture and the extraction solvent into the funnel through the top opening. Do not fill more than two-thirds of the funnel's capacity. Insert the stopper firmly.

Step 3: Invert and vent

Hold the funnel with one hand over the stopcock and one over the stopper. Invert the funnel so the stopcock points upward. Immediately open the stopcock to release any pressure build-up, especially when using volatile solvents. Close the stopcock and shake gently. Invert and vent again. Repeat 4 to 6 times, venting frequently. According to Wikipedia, vigorous shaking can cause an emulsion to form, so always use gentle swirling motions.

Step 4: Allow layers to separate

Return the funnel to its upright position on the stand and remove the stopper to equalise pressure. Allow the two liquid layers to settle completely. This may take a few seconds to several minutes depending on the solvents. A clear interface should be visible between the two layers.

Step 5: Drain the lower layer

Place a receiving flask under the stopcock. Slowly open the stopcock and drain the lower layer into the flask. Close the stopcock precisely when the interface reaches the stopcock, leaving only the upper layer in the funnel. Never discard either layer until the extraction is complete and you have confirmed which layer contains your desired product.

Step 6: Collect the upper layer and repeat

Pour the upper layer out through the top of the funnel into a separate flask. For higher yields, return either layer to the funnel and repeat the extraction with fresh solvent. Combine all fractions containing your product and proceed to drying or evaporation.

Types of Separating Funnels

Separating funnels are available in several shapes, each suited to different applications and workflow preferences.

Squibb (Pear-Shaped)

The most common type. The pear shape narrows toward the stopcock, making it easy to observe the phase boundary and drain the lower layer cleanly. The design ensures the interface sits in the narrow part of the funnel, giving precise control over the drain point.

Best for: General liquid-liquid extraction, organic chemistry

Conical

Has a conical body that tapers from a wide top to a narrow bottom. The wide body provides more surface area between the two phases during shaking, which can improve extraction efficiency. Widely used in academic and industrial labs. Fits standard NS joints and is compatible with most lab stands.

Best for: Efficient extraction, pharmaceutical and industrial use

Cylindrical (Barrel-Shaped)

Straight-sided with a uniform diameter. Less common than Squibb or conical types but used in applications where a uniform cross-section is preferred, such as automated extraction systems. The consistent bore makes flow control more predictable.

Best for: Automated extraction, flow-controlled applications

Plastic (FEP or PP)

Fluorinated ethylene propylene (FEP) funnels offer near-universal chemical resistance, including to HF and strong oxidising acids that would attack glass. Polypropylene funnels are lighter and shatterproof. Both are autoclavable and ideal for hazardous chemical work, trace metal analysis and radiological applications where glass is unsuitable.

Best for: Hazardous chemicals, trace metals, radiological work

How to Choose the Right Separating Funnel

Choose the Right Capacity

Fill the funnel no more than two-thirds full during use. For a 100 mL combined volume of liquids, use a 250 mL funnel. Common sizes are 50, 100, 250, 500, 1000 and 2000 mL. Oversized funnels are difficult to handle; undersized funnels risk spillage during shaking.

Choose PTFE Stopcocks for Solvents

PTFE stopcocks are strongly preferred over glass for most laboratory work. They require no lubrication, are chemically resistant to virtually all common organic solvents and do not seize up when the funnel is stored with solvent inside. Glass stopcocks can stick permanently if stored assembled and require careful greasing.

Choose Glass for Organic Chemistry

Borosilicate glass is the standard material for most extraction work. It is chemically resistant to the majority of organic solvents, acids and bases, and its transparency allows clear observation of phase separation and colour changes during washing steps.

Choose FEP for Aggressive Chemicals

For work involving hydrofluoric acid, strong oxidising agents or applications requiring trace metal cleanliness where glass contamination is a concern, FEP (fluoropolymer) funnels provide unmatched chemical resistance in a break-resistant format.

Separating Funnels Available at LabFriend

LabFriend stocks separating funnels from trusted manufacturers covering glass, FEP plastic, a range of capacities and both Squibb and conical designs, all meeting DIN/ISO standards for laboratory use.

ISOLAB^®

ISOLAB Laborgeräte · Germany

ISOLAB produces a comprehensive range of borosilicate glass separating funnels in both Squibb and conical designs, manufactured to ISO 4800 and DIN 12242 standards. Their funnels feature PTFE stopcocks for reliable chemical resistance and PE conical stoppers. Available from 50 mL to 2000 mL, making them suitable for small-scale research through to preparative work.

✓ ISO 4800, DIN 12242 compliant
✓ PTFE stopcock, borosilicate 3.3 glass
✓ Squibb and conical designs available

ISOLAB Separating Funnel 50 mL, Squibb, PTFE ISOLAB Separating Funnel 250 mL, Conical

Thermo Nalgene^®

Thermo Scientific · USA

Thermo Nalgene FEP separating funnels are manufactured from high-purity fluorinated ethylene propylene, providing near-universal chemical resistance including to hydrofluoric acid and strong oxidising agents. The TFE stopcock is leakproof and requires no lubrication. The translucent body allows clear observation of phase separation. Ideal for radiological, hazardous and trace metal analytical work where glass contamination is a concern.

✓ FEP body, TFE stopcock, ETFE cap
✓ Resistant to virtually all chemicals
✓ Break-resistant, autoclavable

Thermo Nalgene FEP Separatory Funnel 500 mL Thermo Nalgene FEP Separatory Funnel 2000 mL

Lenz Laborglas^®

Lenz Laborglas · Germany

Lenz Laborglas produces high-quality borosilicate 3.3 glass separating funnels in Squibb design with solid glass stopcocks and PE stoppers. Featuring a screwthread retaining device on the stopcock and NS 29/32 standard joints, their range covers 50 mL to 2000 mL in both graduated and non-graduated versions. A solid choice for routine organic chemistry and preparative extraction work.

✓ Borosilicate 3.3 with NS 29/32 joints
✓ Screwthread stopcock retaining device
✓ Graduated and non-graduated options

Lenz Laborglas Separating Funnel 250 mL, Squibb Lenz Laborglas Separating Funnel 1000 mL, Squibb

Browse related categories:

Glass Separating Funnels FEP Separating Funnels Separating Funnel Holders Lab Glassware Guide

Why Purchase From LabFriend?

LabFriend is a trusted global laboratory supply store. When you order from us, you benefit from:

✓ Genuine products from ISOLAB, Thermo Nalgene, Lenz Laborglas and more
✓ Fast global shipping to laboratories worldwide
✓ Competitive pricing with volume discounts for research and education
✓ Expert support to help you select the right funnel for your application

Final Thoughts

The separating funnel is one of the most powerful tools in a chemist's glassware cabinet. By exploiting the simple physical principles of liquid immiscibility and density, it enables clean, controlled and repeatable separations that underpin organic synthesis, purification, environmental analysis and pharmaceutical manufacturing.

Choosing the right funnel comes down to matching the capacity to your volume, selecting PTFE stopcocks for solvent work and choosing glass or FEP based on your chemical requirements. Browse our full laboratory glassware range at LabFriend for separating funnels, extraction equipment and everything else your lab needs.

Frequently Asked Questions

What is the difference between a separating funnel and a dropping funnel?

A separating funnel is used to separate two immiscible liquids by allowing them to form distinct layers and draining one through the stopcock. A dropping funnel is designed to add a liquid slowly and in a controlled manner to a reaction vessel below it. Both have a stopcock, but their purpose and body shape are different. Dropping funnels typically have a cylindrical or pear-shaped body and are mounted above a reaction flask.

Why do I need to vent the separating funnel during shaking?

When you add volatile organic solvents such as diethyl ether, dichloromethane or ethyl acetate to a separating funnel and shake it, the vapour pressure inside builds up rapidly. If the pressure is not released by inverting the funnel and opening the stopcock, the stopper can be forced out violently, causing spills, exposure to solvent vapours or injury. Always vent frequently when using volatile solvents.

What is an emulsion and how do I break it?

An emulsion forms when the two liquid phases become finely dispersed in each other rather than separating cleanly, appearing as a cloudy or milky layer at the interface. This is most common when shaking is too vigorous. To break an emulsion: gently swirl the funnel rather than shaking, add a small amount of saturated sodium chloride (brine) solution to increase the ionic strength of the aqueous phase, or allow the funnel to stand undisturbed for an extended period. In persistent cases, gentle warming or filtration through a pad of sodium sulfate may help.

How do I know which layer is the organic layer?

This depends on the density of the organic solvent. Solvents less dense than water (ethyl acetate: 0.90 g/mL, diethyl ether: 0.71 g/mL, hexane: 0.66 g/mL) form the upper layer. Solvents denser than water (dichloromethane: 1.33 g/mL, chloroform: 1.49 g/mL) form the lower layer. If you are unsure, add a few drops of the funnel contents to a separate vessel of water and observe which phase forms. Never discard either layer until your extraction is complete.

Can a separating funnel be used with acids and bases?

Yes. Borosilicate glass separating funnels are resistant to most acids and bases used in standard laboratory procedures. However, hydrofluoric acid will etch and damage glass. For HF or highly concentrated strong acids, use an FEP funnel such as those in the Thermo Nalgene range. Always ensure your stopcock material is also compatible with the chemicals being used.

How should I store a separating funnel after use?

After cleaning thoroughly with appropriate solvents and then water, allow the funnel to dry completely. For glass stopcocks, remove the stopcock key from the barrel and store it separately. This prevents the key from fusing into the barrel over time due to glass-on-glass contact. PTFE stopcocks can be left assembled but should also be clean and dry. Store the funnel upright in a stand or inverted to prevent dust entering the stopcock barrel.

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