Using the equilibration method, dry oxygen is added to the soil sample in the bag. The sealed, aluminum vaporized bag represents an isothermally closed system in which an isotopic equilibrium between the water contained in the soil sample and the vapor space above the soil sample is established by 24-hour storage. The vapor phase above the soil sample is then measured to determine the isotopic content.

Preparation of the soil samples consists of adding the gas, resealing the bags, and applying small areas of silicone. A major advantage of this method is that the soil sample itself does not have to be processed. Four soil samples are selected for calibration with known laboratory standards. These samples are dried and mixed with water of known isotopic composition before the gas phase is added. After measurement, all samples are oven-dried at 105°C for 24 hours to determine the volumetric water content.

Sample Pration and Measurement

Further information:

Wassenaar, L.I., Hendry, M.J., Chostner, V.L., Lis, G.P., 2008. High-Resolution Pore Water δ 2 H and δ 18 O Measurements by H 2 O (liquid) −H 2 O (vapor) Equilibration Laser Spectroscopy. Environ. Sci. Technol. 42, 9262–9267. https://doi.org/10.1021/es802065s