Contents
Partially compliant

USP ⟨1243⟩ wetting properties of pharmaceutical systems: the new chapter on contact angle, surface tension and surface energy

USP ⟨1243⟩ explains how to measure the wetting of drug powders, tablets, liquids, packaging and devices. The Dropometer measures the three properties the chapter covers: contact angle by sessile drop, surface tension by pendant drop and surface free energy, with ±0.35° contact angle accuracy (Dropometer datasheet). It is partially compliant: it does not run plate, ring or capillary rise techniques, and it has no temperature control.

What brings you here?

Who this is for
Formulation scientists, analytical and QC labs, CDMOs, and packaging and device engineers who need to measure wetting.
Compliance tier
Partially compliant: the Dropometer measures contact angle, surface tension and surface free energy, the properties the chapter covers, by drop shape analysis. It does not run plate, ring or capillary rise techniques.
Measurement
Sessile drop contact angle 10 to 175°, ±0.35° accuracy; pendant drop surface tension up to 75 mN/m, ±0.03 mN/m accuracy (Dropometer datasheet).
Setup
About 2 minutes. Battery powered, 1 kg, runs on the bench in the lab or next to the process.
Last updated
October 20, 2026
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Free one page checklist for USP ⟨1243⟩ style wetting tests: what to prepare, the settings to lock for compacts and liquids, and what to record. Made for formulation and QC labs.

Talk to an expert

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Tell us your API, blend, coating liquid or container and how you judge wetting today. We will measure it live and tell you plainly where the Dropometer fits your method 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 USP ⟨1243⟩
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.

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: USP ⟨1243⟩ and the Dropometer

Standard

USP ⟨1243⟩, Wetting Properties of Pharmaceutical Systems, an informational general chapter of the United States Pharmacopeia, proposed as a draft in Pharmacopeial Forum 49(5) in 2023 by the General Chapters Physical Analysis Expert Committee. It covers contact angle, surface tension of liquids and surface free energy of solids. See the USP-NF chapter listing.

Compliance tier

Partially compliant. The Dropometer measures the end properties the chapter is about: contact angle by sessile drop, surface tension by pendant drop and surface free energy from two or more liquids. Where your method calls for a plate, ring or capillary rise technique, sessile drop and pendant drop are alternative methods, not the method specified; if a contract or customer requires a USP ⟨1243⟩ result by that technique, run a correlation study on your own samples first.

Instrument performance

Contact angle 10 to 175°, accuracy ±0.35°, display resolution 0.01°. Surface tension up to 75 mN/m, accuracy ±0.03 mN/m. Surface free energy up to 100 mN/m. All from the 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

A pharmaceutical CDMO working on spray drying uses the Dropometer for surface tension. Separately, researchers developing an antibacterial resin coating for dental provisional crowns used it for sessile drop water contact angle on cured resin disks (Coatings, 2024). Read our analysis of the paper.

What it does not tell you

A wetting value explains or predicts behaviour. It does not replace dissolution, disintegration or coating quality tests. Pair it with the test your product specification names.

Executive summary: what the new chapter covers and who needs it

What this chapter covers, who uses it and how the Dropometer fits

USP ⟨1243⟩, Wetting Properties of Pharmaceutical Systems, explains how to measure and use the wetting of drug substances, blends, dosage forms, packaging and devices by contact angle, liquid surface tension and solid surface free energy. Formulation scientists, analytical and QC labs, and packaging and device engineers use it to compare materials and explain wetting problems. The Dropometer is partially compliant: it measures all three properties by drop shape analysis, but not every technique the chapter covers. Where your method calls for a plate, ring or capillary rise technique, sessile drop and pendant drop are alternative methods, not the method specified; if a contract or customer requires a USP ⟨1243⟩ result by that technique, run a correlation study on your own samples first.

USP proposed the chapter in Pharmacopeial Forum 49(5) in 2023, from its General Chapters Physical Analysis Expert Committee. The new chapter aims at standardisation of the analytical technology used to characterise wetting, which matters in both batch and continuous manufacturing. It is numbered above 1000, so it is an informational chapter: it carries no mandatory requirement unless a monograph or your own specification cites it. Its sections cover why wettability matters, ways to improve it, surface tension of liquids, contact angle and surface free energy of solids. It sets no universal acceptance limits that we could find, so you set limits from your own products. If you are unsure which test fits, try the measurement method selector.

The Dropometer contact angle and surface energy kit reads sessile drop contact angle from 10 to 175° with ±0.35° accuracy, and pendant drop surface tension up to 75 mN/m with ±0.03 mN/m accuracy (Dropometer datasheet). Surface free energy uses the Fowkes, Equation of State or van Oss Chaudhury Good models in the software. For OWRK, measure the angles on the Dropometer and run OWRK in the free Contact Angle to Surface Energy Calculator, because OWRK is not built into the software. For method background, read the contact angle measurement guide and how to get reproducible contact angle results. Typical values for common surfaces are in our water contact angle reference values.

Further reading: the pharmaceutical guide, thin film and nanocoating surface characterization, the buying guide for goniometers in regulated, high throughput QC, and a pharmaceutical CDMO that uses the Dropometer for surface tension in spray drying.

How the Dropometer fits USP ⟨1243⟩ wetting measurements

Contact angle on a compact, liquid surface tension and surface energy, step by step, in our own words

From a powder or liquid to a recorded wetting value

These steps describe drop shape measurements on the Dropometer. They do not reproduce USP ⟨1243⟩ and do not replace it. Read the current chapter in USP-NF and follow your own validated method for anything you report.

±0.35°

Contact angle accuracy

From the Dropometer product specification. Display resolution is 0.01°.

±0.03 mN/m

Surface tension accuracy

Pendant drop, up to 75 mN/m, static and dynamic. From the Dropometer product specification.

10 fps

Camera frame rate

Readings from about 0.1 s after the drop lands. Fine for fixed time readings, not millisecond absorption studies.

1

Define the question and the conditions

Decide what you need: the angle of water on a solid, the surface tension of a liquid, or the surface energy of a solid. Write down the test liquid, the reading time and how samples are made, so every batch is tested the same way.

2

Prepare compacts, films or surfaces

Press powders into flat compacts at one fixed pressure, or use a cast film, a tablet face or a container surface. Condition samples as your method sets and handle them by the edges. See powder wettability methods for compact versus capillary rise approaches.

3

Set up and check with water

Level the base plate, mount the phone and LED, and fit a clean needle. Hang a pendant drop of pure water and compare its surface tension with the reference value for your room temperature.

4

Place the drop and read at a fixed time

Dispense the same drop volume each time onto the sample. On compacts the drop can soak in or spread, so capture every drop at the same time after it lands. Automatic edge and baseline detection gives the same reading from the same image.

5

Measure the liquid's surface tension

For a binder, coating liquid or dissolution medium, hang a pendant drop and read its surface tension. Enter the liquid density for the Young-Laplace fit, and read each drop at the same drop age.

6

Add surface energy and record

For surface free energy, repeat the contact angle with two or more liquids and use Fowkes, Equation of State or van Oss Chaudhury Good in the software. For OWRK, which is not built in, use the free Contact Angle to Surface Energy Calculator. Record the method, liquids, reading time, sample preparation, room conditions, mean and spread.

7

Watch the full measurement

This video shows a complete Dropometer contact angle measurement, from setup to result. It covers the steps above in one run.

Dropometer contact angle measurement, 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 contact angle accuracy is ±0.35° (Dropometer product specification).

Read the validation papers

Customer evidence

Researchers used the Dropometer for sessile drop water contact angle on an antibacterial dental resin coating, published in Coatings in 2024. A pharmaceutical CDMO uses it for surface tension in spray drying. We have no published client study run to USP ⟨1243⟩ itself.

Read our analysis

Our recommendation: check the setup, then set your own limits

USP ⟨1243⟩ · wetting · formulation and QC

Check the setup before each session with a pendant drop of pure water. 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)). Water reads about 0.15 mN/m lower for each degree warmer (same source), so record room temperature.

USP ⟨1243⟩ is an informational chapter and, as far as public summaries show, sets no universal limits for contact angle or surface energy. So build your own. Measure batches that dissolved, disintegrated or coated well, and batches that did not, then set an internal limit from that correlation. Compacts must be made the same way each time, because pressure and porosity change the angle.

Repeat the study when you change API form, excipient supplier, compaction settings or coating liquid. See reproducible contact angle measurement for bench practice.

Example output

Example data for illustration only. These are not measured results. Your own API, blend, compaction settings and limits decide the numbers.

Example: water contact angle on compacts, three blend batches and the API

Compact Drops (n) Water angle at 1 s (°) Std dev (°) Reading
Blend, reference batch549.71.5Within example limit
Blend, batch 2551.21.9Within example limit
Blend, batch 3563.42.4Above example limit: investigate
API alone582.62.1Poor wetting: hydrophobic API
API with wetting agent557.41.8Wetting agent lowers the angle

How to read this table

Each row is the mean of five drops read 1 s after the drop lands, on compacts made at the same pressure. The example internal limit of 58° was set from a study that linked angle to dissolution on past batches. It is not a USP limit.

Example output chart

The same example data as the table, with the example internal limit marked. The orange bar is above it.

Bar chart of example water contact angles at 1 second on compacts of three blend batches, an API and the API with a wetting agent, with blend batch 3 above an example internal limit of 58 degrees

Example data, not measured results.

Business impact

What changes when wetting is a measured number

Metric Before Dropometer With Dropometer Results
How wetting is judged By eye, or only from dissolution results A contact angle per sample, read from the drop image No published benchmark
Result format Notes such as wets well or poorly An angle per drop, 0.01° display, ±0.35° accuracy Dropometer product specification
Liquid side Surface tension not measured, or a separate ring tensiometer Pendant drop surface tension on the same kit, ±0.03 mN/m accuracy Dropometer product specification
Record Operator note Drop image and value saved per measurement, which can feed into your existing quality records No published benchmark

See the measurement on your own material

Bring a blend that behaved well and one that did not, as compacts or powder. We will measure both live.

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ROI estimate

Estimate the cost of the wetting 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 wetting results between batches, labs or sites

Parameter Recommended Setting Technical Rationale
Test liquid Water, or the medium your method names The angle depends on the liquid. Keep it the same for every batch you compare.
Sample form Compact at one fixed pressure, film, tablet face or container surface Pressure, porosity and roughness change the angle on powders.
Drop volume As your method specifies, fixed for every drop A changing volume adds spread that is not about the material.
Reading time Fixed, for example 1 s after landing Drops soak into compacts and spread with time. The camera captures from about 0.1 s.
Fit model Young-Laplace or polynomial, the same for every run Both are in the Dropometer software. Do not mix them in one study.
Surface energy model Fowkes, Equation of State or van Oss Chaudhury Good; OWRK via the free calculator OWRK and Wu are not built into the software. Use one model for the whole study.
Replicates Several drops per sample, on more than one compact Report mean and spread, not a single drop.
Environment Record room temperature and humidity; condition samples first The Dropometer has no temperature or humidity control and runs at 10 to 45 °C.

Which USP ⟨1243⟩ measurement do you need?

Pick the measurement by the question you need answered

Start: What do you need to know about wetting?

Water contact angle on a solid or compact

Signals:

You want to rank APIs, excipients or blends by how well water wets them, or explain a batch that dissolved slowly.

Rule-out:

Use sessile drop on a compact with the Dropometer, read at a fixed time. See powder wettability: sessile drop on a compressed disk versus Washburn.

Surface tension of a liquid

Signals:

You need the surface tension of a binder solution, coating liquid or surfactant medium.

Rule-out:

Use pendant drop on the Dropometer, up to 75 mN/m. If your method names a ring or plate tensiometer, correlate first.

Surface free energy of a solid

Signals:

You need to know why a liquid wets poorly, through polar and dispersive parts of the surface energy.

Rule-out:

Measure angles with two or more liquids and use Fowkes, Equation of State or van Oss Chaudhury Good in the software. OWRK is not built in: run it in the free calculator. See ASTM D7541.

Loose powder that cannot be compacted

Signals:

Compaction would change the powder, or you need liquid uptake into a powder bed.

Rule-out:

Use a capillary rise (Washburn) method on a force tensiometer. The Dropometer does not run it.

Decision tree at a glance

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

Decision tree for choosing between sessile drop contact angle, pendant drop surface tension, multi liquid surface free energy and Washburn capillary rise for USP 1243 wetting work

Which USP measurement do you need?

Interpreting wetting results for pharmaceutical systems

What the numbers tell you, and what they do not

Lower angle, better wetting: A lower water angle means water spreads more easily, which often goes with faster wetting in disintegration and dissolution.
Time changes the number: On compacts the drop soaks in or spreads. Compare angles only at the same reading time and preparation.
Surface energy explains why: The polar and dispersive parts show whether a wetting agent, coating or process change altered the surface.
Wetting is not performance: A good angle does not prove a batch will dissolve, coat well or meet final product quality. Link it to your own performance data first.
Expert perspective

Why the drop you read decides what you learn

Place a drop and just read it and you get an apparent angle: a value somewhere between advancing and receding that isn't much use. Zisman settled that in the fifties.

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

Compaction pressure, porosity and surface roughness all change the angle on powders. Make every compact the same way.
The camera runs at 10 frames per second. That suits a reading at a fixed time from about 0.1 s, not millisecond absorption studies.
The Dropometer has no temperature or humidity control. Condition samples and liquids, and record room conditions (operating 10 to 45 °C).
Plate, ring and capillary rise techniques are not run on the Dropometer. If your method requires them, correlate drop shape results on your own samples first.
OWRK and Wu are not built into the software. Run OWRK in the free calculator from your measured angles.
No universal limits are published in public summaries of the chapter. Set internal limits from your own correlation study.
FAQ

Frequently asked questions

What does USP ⟨1243⟩ cover?

It is the USP general chapter on wetting properties of pharmaceutical systems. It covers why wetting matters, ways to improve it, surface tension of liquids, contact angle and surface free energy of solids. Its scope runs from drug substances and blends to dosage forms, packaging and devices (source: USP-NF chapter listing).

Is USP ⟨1243⟩ a mandatory test?

Not on its own. USP chapters numbered 1000 to 1999 are informational and non mandatory (source: USP, role of general chapters). It applies when a monograph, your specification or a customer agreement cites it. In GMP work, treat it as guidance for method design, and validate your own method for anything you release on.

Can the Dropometer run USP ⟨1243⟩ measurements?

It is partially compliant. It measures the three properties the chapter covers: contact angle by sessile drop, surface tension by pendant drop and surface free energy from two or more liquids. Where your method calls for a plate, ring or capillary rise technique, sessile drop and pendant drop are alternative methods, not the method specified; if a contract or customer requires a USP ⟨1243⟩ result by that technique, run a correlation study on your own samples first.

How do I measure the contact angle of a pharmaceutical powder?

Press the powder into a flat compact at a fixed pressure, place a water drop and read the angle at a fixed time after it lands. For loose powders that cannot be compacted, a capillary rise (Washburn) method on a force tensiometer is the usual alternative. See powder wettability: sessile drop versus Washburn.

Which surface energy models can I use?

Fowkes, Equation of State and van Oss Chaudhury Good are built into the Dropometer software. OWRK (Owens Wendt Rabel Kaelble) and Wu are not built in: measure the angles on the Dropometer and run OWRK in the free Contact Angle to Surface Energy Calculator.

Why does the angle on my compact keep changing?

Water soaks into the pores and spreads over the surface, so the angle falls with time. Read every drop at the same time after landing. The camera runs at 10 frames per second, so readings start from about 0.1 s.

Does the Dropometer control test temperature for USP ⟨1243⟩ work?

No. The Dropometer has no temperature or humidity control and runs at 10 to 45 °C. Condition samples and liquids to the temperature your method sets, and record room conditions with each result.

Legal note

This page summarises USP ⟨1243⟩ in our own words and does not reproduce the chapter. Read the current USP-NF text before you write a procedure. The Dropometer is partially compliant: it measures contact angle, surface tension and surface free energy by drop shape analysis, not every technique the chapter covers. Droplet Lab does not certify compliance. Your own method validation does.

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How this page was created

Sources, review and tools

Transparency 4 checklist items
01

Sources

USP-NF: General Chapter Wetting Properties of Pharmaceutical Systems (2024 listing); USP-NF: proposed chapter listing (PF, 2023); USP: role of USP general chapters (informational chapters 1000 to 1999); ECA Academy: New USP chapter, Wetting Properties of Pharmaceutical Systems (PF 49(5)), 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. USP ⟨1243⟩ Wetting Properties of Pharmaceutical Systems. doi.usp.org/USPNF/USPNF_M17976_02_01.html
2. USP-NF: <1243> proposed chapter listing (PF, 2023). doi.usp.org/USPNF/USPNF_M17976_10101_01.html
3. USP: role of USP general chapters (informational chapters 1000 to 1999). usp.org/sites/default/files/usp/document/user-forums/01-role-of-usp-ge
4. ECA Academy: New USP chapter, Wetting Properties of Pharmaceutical Systems (PF 49(5)). gmp-compliance.org/gmp-news/new-usp-chapter-wetting-properties-of-phar
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/