Determination of δ²H and δ¹⁸O in saline oil-associated waters: the question of simple vacuum distillation of water samples prior to isotopic analyses

Abstract

The paper deals with analytical and procedural aspects of δ¹⁸O and δ²H determination in saline oil-associated waters. The main objective of the study was to show experimentally the qualitative and quantitative applicability of the simple vacuum distillation of saline oil-associated waters while routine procedures of water isotopic analyses are applied. Additionally, two standard off-line techniques of δ²H determination in water – the zinc and the chromium method – have been compared. Each time a typical isotope salt effect has been tracked on the Dead Sea water. The results clearly show that application of the simple vacuum distillation improve the accuracy and reproducibility of δ²H determinations, especially in chromium off-line technique which appeared to be more sensitive to water salinity. The simple vacuum distillation does not improve the quality of δ¹⁸O determinations in the range of water salinities studied. Its application to high concentrated brines (for example, Dead Sea water) decreases the time of equilibration but still propagate the isotopic error connected with low water activity (in the case of ¹⁸O/¹⁶O ratio) and the incomplete water extraction from the remaining salts (in the case of ²H/¹H ratio); in consequence, its time-consuming application seems to be baseless.

Keywords:

• Hydrogen-2
• chromium method
• Oxygen-18
• oil-associated waters
• salt effect
• vacuum distillation
• zinc method

Acknowledgements

The authorities of the Helmholtz Centre for Environmental Research UFZ in Halle, Germany, as well as of the Institute of Geological Sciences Polish Academy of Sciences in Warsaw, Poland, are thanked for making opportunity for this kind of experimental study.

The technical stuff of the UFZ are also thanked for their help in the research.