Contents
Partially compliant

EN 14210: interfacial tension of surfactant solutions by the ring or stirrup method

EN 14210 measures the interfacial tension between a surfactant solution and an oil or other liquid that does not mix with water, with a ring or a stirrup, over 4 to 50 mN/m. The Dropometer measures interfacial tension by pendant drop with the optional cuvette, so it gets the same end result by an alternative method. Pendant drop is an alternative method, not the stirrup or ring method the standard specifies; if a contract or customer requires an EN 14210 result, run a correlation study on your own samples first.

What brings you here?

Who this is for
Surfactant and emulsifier makers, detergent, crop protection and emulsion formulators, and university colloid groups.
Compliance tier
Partially compliant: the Dropometer measures interfacial tension by pendant drop with the optional cuvette. That is an alternative to the ring or stirrup method EN 14210 specifies.
Measurement
Interfacial tension by pendant drop of one liquid inside another, with the optional cuvette. No accuracy figure or range is published for it (Dropometer datasheet).
Setup
About 2 minutes. Battery powered, 1 kg, runs on the lab bench or beside the plant.
Last updated
October 18, 2026
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Free one page checklist for pendant drop interfacial tension with the optional cuvette next to EN 14210: what to prepare, the settings to lock, the blank to run and what to record. Made for surfactant and emulsifier QC benches.

Talk to an expert

Book a 15-minute consult about your oil and surfactant

Tell us your surfactant, your oil and how you test them today. We will measure the pair live by pendant drop in the optional cuvette and tell you plainly where the Dropometer fits next to your ring or stirrup tensiometer and where it does not.

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View the official standard
Gurdeep-Saini-Photo
Written by
Gurdeep Singh Saini
Holds a BASc in Mechanical Engineering from Ryerson University (now Toronto Metropolitan University) and an MASc from York University. He develops the automatic edge and baseline detection behind the Dropometer's analysis.
COO at Droplet Lab
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Droplet-Lab logo
Technical Review by
Droplet Lab Team
Droplet Lab builds precision instruments and software for surface science measurement, specialising in contact angle analysis and surface tension characterisation. Used by researchers across materials science, pharmaceuticals, coatings, and advanced manufacturing, Droplet Lab's Dropometer has contributed to studies published in peer-reviewed journals including Advanced Functional Materials (Impact Factor 19). The team combines instrument engineering with deep domain knowledge in wettability science with a focus on practical accuracy.
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Verified against EN 14210
Gurdeep-Saini-Photo
Written By

Gurdeep Singh Saini

COO at Droplet Lab

Holds a BASc in Mechanical Engineering from Ryerson University (now Toronto Metropolitan University) and an MASc from York University. He develops the automatic edge and baseline detection behind the Dropometer's analysis.

Thesis Design and implementation of environment chamber for interfacial phenomenon processes
Droplet-Lab logo
Reviewed By

Droplet Lab Team

Droplet Lab builds precision instruments and software for surface science measurement, specialising in contact angle analysis and surface tension characterisation. Used by researchers across materials science, pharmaceuticals, coatings, and advanced manufacturing, Droplet Lab's Dropometer has contributed to studies published in peer-reviewed journals including Advanced Functional Materials (Impact Factor 19). The team combines instrument engineering with deep domain knowledge in wettability science with a focus on practical accuracy.

Featured Studies & Publications

Research Paper Contact angle measurement with a smartphone
Research Paper Surface tension measurement with a smartphone using a pendant drop

Evidence box

Standard

EN 14210:2003, Surface active agents: determination of interfacial tension of solutions of surface active agents by the stirrup or ring method, from CEN/TC 276. The listing gives a range of 4 to 50 mN/m between two liquids that do not mix. CEN confirmed it in 2024. In Germany, DIN EN 14210 replaced DIN 53993.

Compliance tier

Partially compliant. The Dropometer gets the end result the standard is after: interfacial tension, by pendant drop with the optional cuvette. Pendant drop is an alternative method, not the stirrup or ring method the standard specifies; if a contract or customer requires an EN 14210 result, run a correlation study on your own samples first.

Instrument performance

Interfacial tension runs by pendant drop with the optional cuvette; the Dropometer product specification gives no accuracy figure or range for it. Surface tension in air, used for the daily water check, reads up to 75 mN/m with ±0.03 mN/m accuracy (Dropometer product specification).

Peer reviewed method

The drop shape method is validated against a KRUSS DSA100E in two peer reviewed papers. See our validation publications.

Customer evidence

Researchers studying emulsion phase inversion used the Dropometer to measure pendant drop interfacial tension of anionic, cationic, non ionic and zwitterionic surfactant solutions and cellulose nanocrystal suspensions in a cuvette of oil (Colloids and Interfaces, 2025). Read our analysis of the paper.

What it does not tell you

Interfacial tension shows how far a surfactant lowers the tension between two liquids. It does not predict emulsion stability on its own, which also depends on droplet size and the film around each droplet. Pair it with your stability test.

Executive summary

What this standard measures, who uses it and how the Dropometer fits

EN 14210 measures the interfacial tension between a solution of surface active agents and a second liquid that does not mix with it, such as an oil, by pulling a stirrup or a ring through the interface. Surfactant and emulsifier makers, detergent and crop protection formulators and university colloid groups use it to compare how far a surfactant lowers the tension between water and oil. The Dropometer is partially compliant: it measures interfacial tension by pendant drop with the optional cuvette, the same end result by a different method. Pendant drop is an alternative method, not the stirrup or ring method the standard specifies; if a contract or customer requires an EN 14210 result, run a correlation study on your own samples first.

EN 14210:2003 is the European standard from CEN/TC 276, adopted nationally as BS EN 14210 and DIN EN 14210, and CEN confirmed it in 2024. Its listing gives a range of 4 to 50 mN/m and says the methods suit water or aqueous solutions against organic liquids that do not mix with water. The stirrup is sometimes translated as a bow, from the German Bügel. For background on the molecules involved, read our guide to understanding surfactants and the chemicals guide.

The Dropometer pendant drop tensiometer hangs a drop of the denser liquid inside the lighter liquid in the optional cuvette, then fits the drop shape. No accuracy figure or range is published for interfacial tension on the Dropometer, so your correlation data sets the limits. Formulators use the value to rank emulsifiers before long stability tests, as in emulsion stability and phase separation control. Researchers used the Dropometer with a cuvette of oil to measure the interfacial tension of surfactant and cellulose nanocrystal solutions in an emulsion study, and a university rheology lab uses the Dropometer for pendant drop surface tension.

Further reading: the surface tension measurement guide, reproducible surface tension measurement, choosing a tensiometer for surfactant and CMC research, CMC reference values for common surfactants and a classroom experiment on how surfactants change surface tension.

How the Dropometer fits the workflow

Pendant drop interfacial tension of surfactant lots against your oil, with the optional cuvette, step by step

From two liquids to a lot decision

These steps describe a pendant drop measurement on the Dropometer with the optional cuvette. They are not the ring or stirrup procedure of EN 14210 and do not replace it. Buy the current edition and follow it for any result you report to the standard.

Optional cuvette

Interfacial tension

A pendant drop of the denser liquid hangs inside the lighter one. No accuracy figure is published for it.

10 fps

Camera frame rate

Readings over drop age from about 0.1 s. Fine for surfactant ageing, not millisecond studies.

About 2 min

Setup

Base plate, phone holder, LED and syringe. No PC needed.

1

Prepare and condition the liquids

Make up each surfactant lot at the same concentration in water of the quality your method names. Use the same batch of oil for the whole series. Condition both liquids to room temperature, or the temperature the standard specifies, and note the density of each at that temperature.

2

Set up and check with water

Level the base plate, mount the phone and LED, and fit a clean needle. Hang a drop of pure water in air and compare it with the reference value for your room temperature before you test anything else.

3

Fill the optional cuvette and run a blank

Fill the clean optional cuvette with the lighter, clear liquid, usually the oil. Lower the needle into it and hang a drop of pure water. A steady reading confirms the oil and glassware are clean.

4

Hang the drop and let it age

Fill the syringe with the first lot, hang a drop large enough to show a clear neck, and enter both densities. Surfactant needs time to reach the interface, so read every drop at the same age, or follow it until the value settles.

5

Read and repeat

The software fits the Young-Laplace equation to the drop profile. Automatic edge detection gives the same reading from the same image. Read several fresh drops per lot, reject drops with bubbles or a poor fit, and rinse the syringe and needle between lots.

6

Record and report the method

Record the method as pendant drop with the optional cuvette, plus both liquids, densities, drop age, room temperature, the blank, and mean with spread. State that these are not ring or stirrup results to EN 14210. See reproducible surface tension measurement for good bench practice.

7

Watch the full measurement

This video shows a complete Dropometer pendant drop surface tension measurement, from setup to result. It covers the steps above in one run.

Dropometer pendant drop surface tension, start to finish.

Validated measurement approach

Independent benchmarking and publication-based validation references.

Peer reviewed method

The Dropometer drop shape method is validated against a KRUSS DSA100E in two peer reviewed papers, one in Review of Scientific Instruments and one in Colloids and Surfaces A. Published surface tension accuracy is ±0.03 mN/m (Dropometer product specification); no figure is published for interfacial tension.

Read the validation papers

Customer evidence

A university research team used the Dropometer with a cuvette of oil to measure pendant drop interfacial tension of surfactant and nanocrystal solutions, in a study of emulsion phase inversion published in Colloids and Interfaces in 2025. We have no published client study run to EN 14210 itself.

Read our analysis

Check water, run a blank, then correlate

EN 14210 · interfacial tension · surfactant and emulsifier QC

Check the setup with pure water in air before each session. The reference surface tension is 72.74 mN/m at 20 °C and 71.97 mN/m at 25 °C (source: IAPWS R1-76(2014)). This checks needle scale, focus and fit. It is a surface tension check, not an interfacial tension check.

Next, hang a drop of pure water inside your clean oil in the optional cuvette and read it a few times as it ages. With clean liquids the value holds steady. A value that keeps falling points to surface active impurities in the oil, the water or the glassware. Record this blank with every series.

EN 14210 is a test method and publishes no pass or fail limit. Your product specification or your customer sets the limits. Its listed range is 4 to 50 mN/m (source: EN 14210:2003 listing). Stirrup or ring values can differ from pendant drop values, because each method reads the interface in a different way and at a different age. Pendant drop is an alternative method, not the stirrup or ring method the standard specifies.

If you work to an EN 14210 limit, run a correlation study. Measure the same pairs of liquids on your ring or stirrup tensiometer and on the Dropometer with the optional cuvette, at the same temperature, then set your pendant drop limits from that data. Repeat it when you change surfactant family, oil or test temperature. See reproducible surface tension measurement for bench practice.

Example output

Example data for illustration only. These are not measured results. Your own surfactant, oil, water quality and temperature decide the numbers.

Example: emulsifier lots at 0.1% in water against a light oil, pendant drop in the optional cuvette

Sample Drops (n) Mean interfacial tension (mN/m) Std dev (mN/m) Note Decision
Pure water (blank)548.60.2Steady over drop age: oil is cleanBlank passes
Lot 1 (reference lot)58.40.1Sets the example bandAccept
Lot 258.90.2Inside 7.6 to 9.2Accept
Lot 3512.70.2Above 9.2: weaker at the interfaceHold the lot, investigate
Lot 4 (new supplier)53.20.1Below 4: outside the EN 14210 rangeReview with your customer

How to read this table

Each row is the mean of five drops of the aqueous phase hanging in the same example light oil, read at the same drop age at 22 °C room temperature. The example accept band of 7.6 to 9.2 mN/m is the reference lot value of 8.4 mN/m plus or minus 0.8 mN/m, set from an example correlation and capability study. Values below 4 mN/m sit outside the EN 14210 range.

Example output chart

The same example data as the table, with the example accept band and the EN 14210 range marked.

Bar chart of example interfacial tension against a light oil: water blank 48.6, lot 1 8.4, lot 2 8.9, lot 3 12.7 and lot 4 3.2 mN/m, with the 50 mN/m upper end of the EN 14210 range and a 9.2 mN/m example accept limit marked

Example data, not measured results.

Business impact

What changes when pendant drop sits next to your ring or stirrup tensiometer

Metric Before Dropometer With Dropometer Results
Liquid per reading A measuring vessel with both liquid layers A syringe of the aqueous phase and a cuvette of oil No published benchmark
Interface age One reading per pull Readings over drop age from about 0.1 s Dropometer product specification, 10 frames per second
Record Force reading with ring or stirrup corrections Drop image and fitted value saved per drop No published benchmark
Reported EN 14210 value Ring or stirrup tensiometer Still needs the ring or stirrup tensiometer, or a correlation study EN 14210 title and scope

See the measurement on your own oil

Bring a surfactant lot that performed well, one that did not, and the oil you test against. We will measure both pairs live.

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ROI estimate

Estimate the cost of the emulsifier lot and formulation failures this test can catch

Enter your own numbers. The defaults are examples, not Droplet Lab results.

Quality cost snapshot

Estimate what wetting related failures cost you.

Example only. Use what you see in a trial on your own samples.
Your own figure.
Your own estimate.

Result

~0
Estimated annual cost today
~0
Estimated annual cost avoided
~0
Payback period

Annual exposure combines audit/CAPA cost, customer rejections, and recall probability; avoided exposure applies the risk reduction percentage.

Method settings

Lock these before you compare pendant drop results between lots, runs or sites

Parameter Recommended Setting Technical Rationale
Method Pendant drop with the optional cuvette, reported as an alternative method EN 14210 specifies a ring or stirrup.
Liquid pair Aqueous phase as the drop, the lighter clear oil in the cuvette The drop must hang in the liquid around it, and the camera must see through that liquid.
Densities Both liquids, measured at the test temperature The Young-Laplace fit uses the density difference. An error here moves every result.
Drop age at reading Fixed for every drop, or read once steady Surfactant keeps arriving at the interface, so the value falls with age.
Fit model Young-Laplace The fit for a pendant drop profile in the Dropometer software.
Blank Pure water in the same oil, every series A falling blank shows contamination before it shows up as a bad lot.
Replicates Several fresh drops per lot; rinse between lots Report mean and spread. Surfactant left in the needle lowers the next reading.
Range EN 14210 covers 4 to 50 mN/m Below about 4 mN/m, consider a spinning drop tensiometer and check with your customer.
Environment Record room temperature; condition both liquids first The Dropometer has no temperature control and runs at 10 to 45 °C.

Is EN 14210 the right test?

Pick the method by the question you need answered

Start: What do you need to know about your two liquids?

Emulsifier lot QC or screening against your oil

Signals:

You want an interfacial tension per lot or per candidate against the oil in your product, for QC or R&D.

Rule-out:

Use pendant drop with the optional cuvette on the Dropometer, and name the method in your records. See emulsion stability and phase separation control.

A reported EN 14210 value

Signals:

Your customer, contract or specification asks for an interfacial tension measured to EN 14210.

Rule-out:

The standard specifies a ring or stirrup tensiometer. Pendant drop is an alternative method: run a correlation study on your own samples before you report against an EN 14210 limit. For the ISO equivalent, see ISO 6889.

Very low tension, as in microemulsions

Signals:

Your values fall below about 4 mN/m, under the EN 14210 range, and drops detach or barely hold a neck.

Rule-out:

Use a spinning drop tensiometer. The Dropometer does not run spinning drop.

Surface tension against air, or a CMC

Signals:

You need the surface tension of the solution itself, or the concentration where micelles form.

Rule-out:

Use pendant drop in air on the base kit. See EN 14370 for surface tension and ISO 4311 for the CMC.

Decision tree at a glance

Start from the question you need answered. Blue boxes are measurements the Dropometer runs.

Decision tree for choosing between pendant drop with the optional cuvette for emulsifier lot checks, a ring or stirrup tensiometer or a correlation study for reported EN 14210 values, a spinning drop tensiometer below 4 mN/m, and pendant drop in air for surface tension or a CMC

Is EN 14210 the right test?

Interpreting results

What an interfacial tension value tells you, and what it does not

Lower value, more active at the interface: A surfactant that lowers the tension between water and oil further packs more strongly at that interface.
A lot that reads high is weaker: Against the same oil and concentration, a higher value than the reference lot points to lower activity or a change in composition.
The oil matters: Values only compare against the same oil. Change the oil and the whole scale moves.
Methods can disagree: Ring, stirrup and pendant drop values on the same pair of liquids can differ. Correlate before you compare them.
Expert perspective

Why the tension between oil and water shows what a surfactant does

Plot surface tension against surfactant concentration and the interface tells you when it is saturated: the curve bends at the point where the surface can hold no more.

Dr. Alidad Amirfazli

Department of Mechanical Engineering, York University, Co-founder and Scientific Advisor, Droplet Lab

Common pitfalls and limits

Honest limits of the method and of the Dropometer

Pendant drop is an alternative method, not the stirrup or ring method the standard specifies; if a contract or customer requires an EN 14210 result, run a correlation study on your own samples first.
No accuracy figure or range is published for interfacial tension on the Dropometer. Set limits from your own correlation study.
The outer liquid in the optional cuvette must be clear, and the two densities must differ clearly, or the drop shape cannot be fitted well.
The Dropometer has no temperature control. Condition both liquids and record room temperature (operating 10 to 45 °C).
Trace surfactant in the oil, glassware or needle lowers readings. Run the water blank in each series and rinse between lots.
The camera runs at 10 frames per second. That suits readings from about 0.1 s of drop age, not millisecond adsorption studies.
FAQ

Frequently asked questions

What does EN 14210 measure?

It measures the interfacial tension between a solution of surface active agents and a second liquid that does not mix with it, from 4 to 50 mN/m. A ring or stirrup is pulled through the interface on a force tensiometer, with the corrections the standard specifies. The listing says it suits water or aqueous solutions against organic liquids (source: EN 14210:2003 listing).

Can the Dropometer run EN 14210?

It gets the same end result by a different method, so it is partially compliant. It measures interfacial tension by pendant drop with the optional cuvette. Pendant drop is an alternative method, not the stirrup or ring method the standard specifies; if a contract or customer requires an EN 14210 result, run a correlation study on your own samples first.

Is EN 14210 the bow or ring method for surface tension?

Bow is another translation of the stirrup, from the German Bügel. But EN 14210 covers interfacial tension between two liquids, not surface tension against air. For surface tension of surfactant solutions, see EN 14370. The Dropometer measures both: surface tension in air on the base kit, interfacial tension with the optional cuvette.

How is EN 14210 different from ISO 6889?

Both measure the interfacial tension of surfactant solutions against a second liquid with a stirrup or ring. EN 14210 is the European standard from CEN/TC 276; ISO 6889 is the ISO method. Quote the one your customer names. See ISO 6889.

Is EN 14210 still current?

Yes. EN 14210:2003 is current, and CEN confirmed it in October 2024 (source: EN 14210:2003 listing). National versions include BS EN 14210 and DIN EN 14210, which replaced DIN 53993 in Germany (source: DIN Media listing).

How do I measure interfacial tension with the Dropometer?

Use the optional cuvette. Fill it with the lighter, clear liquid, hang a drop of the denser liquid from the needle inside it and enter both densities. The software fits the drop shape. No accuracy figure or range is published for interfacial tension, so correlate with your ring or stirrup results before you compare values.

Does the Dropometer control test temperature?

No. The Dropometer has no temperature control and runs at 10 to 45 °C. Condition both liquids to the temperature your method sets, record room temperature with each result, and use densities measured at that temperature.

Harvard University
Eli Lilly
Zeus
DuPont
Essilor Luxottica
Raytheon
Cornell University
P&G
Axiom Space
Lululemon
Holcim
CNRS France
FLIR
Avery Dennison
US DOE
BRP
Heraeus
Singapore Institute of Technology
East China University
Indian Institute of Science
NRC Canada

Legal note

This page summarises EN 14210 in our own words and does not reproduce the standard. Buy the current edition from your national standards body before you write a procedure. The Dropometer is partially compliant: it measures interfacial tension by pendant drop with the optional cuvette, an alternative to the ring or stirrup the standard specifies. Droplet Lab does not certify compliance. Your own method validation and correlation study do.

View the official standard Book a 15-minute consult

How this page was created

Sources, review and tools

Transparency 4 checklist items
01

Sources

CEN EN 14210:2003 listing and scope (iTeh Standards); BSI listing: BS EN 14210:2003; DIN Media listing: DIN EN 14210:2004-03 (replaces DIN 53993); Genorma: EN 14210:2003 status, confirmed October 2024, the Dropometer product specification and Droplet Lab validation papers.

02

Drafting assistance

Drafted with Claude (Anthropic) from the sources listed, then reviewed by Droplet Lab.

03

What we did not do

We did not copy text from the standard. Buy the current edition for the full procedure.

04

Last checked

October 2026

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References

1. EN 14210:2003. iteh.es/catalog/standards/cen/98f58421-7aa3-4989-8222-8549f6444a3c/en-14210-2003
2. BSI listing: BS EN 14210:2003. knowledge.bsigroup.com/products/surface-active-agents-determination-of
3. DIN Media listing: DIN EN 14210:2004-03 (replaces DIN 53993). dinmedia.de/en/standard/din-en-14210/64584985
4. Genorma: EN 14210:2003 status, confirmed October 2024. genorma.com/en/standards/en-14210-2003
5. Droplet Lab. Peer reviewed validation papers in Review of Scientific Instruments and Colloids and Surfaces A. dropletlab.com/validation/publications/
6. Droplet Lab. Dropometer product specification, 2026. dropletlab.com/products/dropometer/