A method to extract soil water for stable isotope analysis

A method has been developed to extract soil water for determination of deuterium (D) and ¹⁸O content. The principle of this method is based on the observation that water and toluene form an azeotropic mixture at 84.1°C, but are completely immiscible at ambient temperature. In a specially designed distillation apparatus, the soil water is distilled at 84.1°C with toluene and is separated quantitatively in the collecting funnel at ambient temperature. Traces of toluene are removed and the sample can be analyzed by mass spectrometry. Kerosene may be substituted for toluene. The accuracy of this technique is ± 2 and ± 0.2‰">± 0.2‰, respectively, for δD and δ¹⁸O. Reduced accuracy is obtained at low water contents.