Dissolved gas analysis
At Isolab, we analyze the composition and stable isotopes of gas, dissolved in water samples.
Sample Collection and Equilibration
Water samples are collected by the client and delivered in Isoflasks. Over time, gases dissolved in the water, partition into the free headspace above the liquid. After ca. 2 days at a stable temperature, an equilibrium is established between the dissolved gas and the headspace gas.
This equilibrium can be described and calculated using Henry’s Law.
Henry’s Law
Henry’s Law states that the concentration of a gas dissolved in a liquid is directly proportional to the partial pressure of that gas in the headspace.
Read for more information the publication Sander, R.: Compilation of Henry's law constants (version 5.0.0) for water as solvent, Atmos. Chem. Phys., 23, 10901–12440, https://doi.org/10.5194/acp-23-10901-2023, 2023.
Or visit the website www.henrys-law.org
Gas Composition Analysis
From the headspace gas, we measure the composition of all major gas components (e.g., CO₂, N₂, O₂, methane and other hydrocarbons, if present). Combined with:
- Temperature
- Air pressure
- Water volume
- Headspace volume
…we calculate the original dissolved concentrations of the gases in the water.
Stable Isotope Analysis
If sufficient gas is present in the sample, we can also measure stable isotopes of selected components:
| Gas Component | Isotopes Measured |
| Methane (CH₄) | δ¹³C (carbon isotopes), δD (hydrogen isotopes) |
| CO₂ (if present in sufficient quantity) | δ¹³C |
These measurements provide powerful insights into gas origin, biological processes, and geochemical conditions in the water body.
