A New Vacuum-distilled Extraction Apparatus for Desert Soil Water and Its Application

The stable isotopic technique is a good tool to trace information on soil water movement in arid and semi-arid regions. Soil water extraction, rather than isotopic measurement, is the bottleneck in this technique. To solve this problem, a new device has been developed, based on the conventional vacuum extraction in our laboratory. The new device is mostly composed of glass tubes with two parallel connections. The combination of vacuum extraction and liquid nitrogen condensation was applied to collect soil water and the working vacuum was improved to around 0.5 Pa from 5 Pa. For this new device, which is better than other devices, the maximum load capacity of the soil sample and the maximum collection volume of soil water were 600 g and 15 mL respectively. A series of experiments show that the standard deviation of δD and δ¹⁸O are both less than 1‰, indicating a good quality for this new device. These experiments also demonstrate that it takes only 20 min to completely extract soil water from desert sand at 105℃ without significant mass fractionation. This new device is more flexible for various extractions of samples with different weights and moistures with a good water recovery, and is also characterized by a low cost, simple operation and cheap maintenance. Compared with the conventional device, the work efficiency of the new device has been doubled. In addition, the extractions of field samples and isotopic investigations further demonstrate the importance of the new device in the study of isotope hydrology.