A Soil Water Extraction Method with Accelerated Solvent Extraction Technique for Stable Isotope Analysis

Soil water is one of the most important components in hydrological cycle. The stable isotopes (e.g., deuterium, 2H, oxygen-18, 18O) in soil water have been increasingly used as natural tracers in the ecological, environmental and hydrological research. In view of different techniques for extracting soil water, there are significant differences in the δD and δ18O compositions. This paper presents a method for the accelerated solvent extraction (ASE) of soil water for stable isotope analyses by mass spectrometry. The optimum parameters of extracting soil water were as follows: dichloromethane as the extraction solvent, temperature of 100 °C, pressure of 10.3 MPa, static time of 10 min. The samples were extracted three times, and with cycle values four, four and three, respectively. The extracted water was enriched in deuterium and oxygen-18 by 2.12%–4.58% and −0.17%–0.93%, respectively, compared with the added water. The reproducibility of replicate extractions of soil water was around ±0.89% for δD and ±0.37% for δ18O.

The isotopic compositions of extracted water were enriched by 3.6% for δD and 0.36% for δ18O by ASE method, and 1% for δD and 0.49% for δ18O by USC method. Both methods yielded similar precision and accuracy. But USC could not extract enough water from soil samples with low water content (6.3% and 4.8%). The ASE extraction method could be performed to extract water with low content in soil samples with higher accuracy.Figure optionsDownload as PowerPoint slide