What Are Stable Isotopes?

Atoms are made up of a nucleus with protons and neutrons, surrounded by orbiting electrons. The number of protons determines the chemical identity of an element, while the neutrons affect its stability. Atoms of the same element that have different numbers of neutrons are called isotopes.

Some isotopes are stable, meaning they do not break down over time. Others are radioactive, meaning they decay into different elements. For example, carbon has three common isotopes:

• Carbon-12 (¹²C) and Carbon-13 (¹³C) are stable.
• Carbon-14 (¹⁴C) is radioactive and decays into nitrogen over time.

Why Are Stable Isotopes Important?

Even though isotopes of the same element behave similarly in chemical reactions, their physical properties differ slightly due to their different masses. This small difference affects:

• Diffusion rates (lighter isotopes move faster).
• Bond strength (heavier isotopes form stronger bonds).
• Fractionation, a process where isotope ratios change due to chemical and physical reactions.

By measuring these isotope ratios, we can gain valuable insights into natural processes.

Stable Isotope Analysis at Isolab

At Isolab, we specialize in measuring the ratios of key light element isotopes:

• Hydrogen (²H/¹H)
• Carbon (¹³C/¹²C)
• Nitrogen (¹⁵N/¹⁴N)
• Oxygen (¹⁸O/¹⁶O)

Because isotope ratio differences between samples are very small, they are reported as δ-values (per mill, ‰), which compare a sample’s isotope ratio to an internationally recognized standard.

Applications of Stable Isotope Measurements

1. Identifying the Origin of Methane

Methane (CH₄) can be produced in different ways:

• Bacterial methane (e.g., from swamps or digestion processes) is rich in ¹²C, resulting in very low δ¹³C values (down to -80‰).
• Thermogenic methane (formed deep underground) has a higher δ¹³C value (around -30‰).
  By analysing δ¹³C, we can determine whether methane comes from biological activity or geological sources.

2. Detecting Food Adulteration

Stable isotope analysis can verify food authenticity:

• Different plants use distinct photosynthesis processes, which affect their carbon isotope composition.
• For example, cane and corn sugar have higher δ¹³C values (-14 to -10‰) compared to beet sugar (-28 to -22‰).
• This allows us to detect if honey has been mixed with cheaper corn syrup, as corn syrup raises the δ¹³C value.
• Similarly, organic food can be identified by measuring δ¹⁵N:
  • Artificial fertilizers have δ¹⁵N values close to 0‰.
  • Organic manure has higher δ¹⁵N values, which are absorbed by crops.

3. Tracing Water Sources

The isotope composition of water changes as it moves through the environment:

• Ocean water has δ¹⁸O and δ²H values of 0‰.
• As water evaporates, lighter isotopes evaporate first, leaving heavier isotopes behind.
• When clouds form and move inland, rainwater becomes progressively lighter (more negative δ-values) the further it travels from the coast.
• By measuring δ¹⁸O and δ²H, we can determine where a water sample originated or where an organism consumed its water.

How Can Stable Isotope Analysis Help You?

Stable isotope measurements provide unique insights that go beyond standard chemical analysis. Whether in geology, ecology, food authenticity, or oil and gas exploration, isotopes reveal information that traditional methods cannot.

If you’re interested in applying stable isotope analysis to your research, contact Isolab to discuss how our expertise can support your work.

Suitable sample containers for composition and isotope analysis

Version: 1 July 2025

Isolab recommends the following sample containers for various types of samples.

Pressurized cylinders for gas samples

Gas samples are best conservated in pressurized cylinders. We prefer cylinders with a volume of 150-500ml, pressurized to 5-10 bars, with a ¼” Swagelok connection.

Figure 1 - A 300ml and a 150ml Swagelok cylinder

These kinds of cylinders can be ordered from Swagelok: www.swagelok.com.

Labco vials for small amounts of gas

Vials for very small amounts of gas can be ordered at: www.labco.co.uk/

Gasbags for gas samples

Not all brands of gasbags are reliable for isotopes and for small molecules. We have very good experiences with the gasbags from Calibond gasbags from Calibrated Instruments.

Figure 2 - A calibond gasbag from Calibrated Instruments

These bags can be ordered at: https://calibrated.com/

Isotech containers

	Container	Purpose
	Isotube	Flowline gas samples (mudgas) and produced gas samples
	Isojar	Cuttings/soil samples with headspace
	Isoflask	Water samples for analysis of dissolved gas

• Can be ordered at: www.isotechlabs.com
• Dutch distributor: http://www.bio-connect.nl

Minimum detection limits for gas composition and isotope analysis at Isolab.

The listed numbers are an indication and depend on the sample matrix.

Gascomposition

Carbon and hydrogen Isotopes

Other isotopes

If necessary, cryogenic enrichment is used without additional charges.

Samples can be sent to

Isolab B.V.
Heesterseweg 29
5386 KT Geffen
The Netherlands

More information and instructions follow....