Against the background of increasing use of stable water isotopes in hydrogeochemical research sciences, the Institute of Landscape Ecology and Resources Management (ILR) constructed a cryogenic vacuum extraction device. With the principle of cryogenic vacuum extraction, it is possible to determine the isotopic signature of environmental water, more precisely, of soil and plant water serving as pools of local water cycles by extracting their water under vacuum. In the extraction process, the sample is heated under a defined vacuum, which leads to a water evaporation from the soil, i. e. plant sample. Afterwards, the evolved vapour is frozen in a liquid nitrogen (cryogenic) cold trap (Ingraham and Shadel, 1992). After defrosting the obtained sample water, its isotopic signature is analysed via diode laser absorption spectroscopy (Los Gatos Research DLT-100- Liquid Water Isotope Analyser, Los Gatos Research Inc., 67 East Evelyn Avenue, Suite 3, Mountain View, CA, 94041-1529, US).Among the existing water extraction methods for soil and plant samples, cryogenic vacuum extraction is one of the most widely used methods (Peters and Yakir, 2008).Hence, the aim of this thesis was to create a vacuum-tight, reliable, and user-friendly cryogenic vacuum extraction device with an extendable modularity and several independently working extraction units for application in stable water isotope research science and, furthermore, to specify this apparatus through validation experiments.The constructed vacuum extraction device of the ILR is mainly based on the principle used by West et al. (2006) and by the Paul Scherrer Institute (PSI, Villigen, CH). Implying that an apparatus with independently working extraction units - basically consisting of stainless steel Swagelok® fittings for realising the vacuum-tightness and glassware for a visual observation of the extraction process - was build.Beyond the execution of the existing devices, the extraction apparatus is additionally equipped with a mechanism for high-purity nitrogen aeration. This execution prevents the loss of water vapour during defrosting after extraction by purging every sample with high-purity nitrogen gas after the water extraction procedure. Moreover, the aeration of the vacuum system with high-purity nitrogen gas instead of aeration with atmospheric air, overcomes the risk of a mixture of atmospheric water vapour with the extracted sample water. Nitrogen gas, as an inert gas, does not react with the extracted water, but serves as a protective layer over the extracted defrosting sample water, minimising the error of isotope fractionation.The new vacuum extraction device was tested in order to specify it. The concern of the validation experiments was to examine whether the water isotopic signature is changed through the extraction process, whether the high-purity nitrogen aeration affects the water isotopic composition, and whether cross-contamination among the six extraction units occurs.All validation tests were conducted with water three different types of water with known isotopic composition - instead of soil or plant material for an easier implementation of the experiments and better comparability of the results.The validation experiments revealed that the constructed cryogenic vacuum extraction device is vacuum-tight and, consequently, there was no change in the isotopic signature of the extracted water due to a complete water extraction process. As expected, the high-purity nitrogen aeration after the water extraction did not change the isotopic signature of the extracted sample water, but could contribute to a better distribution of the values for the water isotopic signatures and, therefore, to a higher accuracy. Finally, while extracting two different types of water during one extraction process, no exchange among these waters could be observed, concluding that no cross-contamination among the six independent extraction units occurred.Summarising, the constructed cryogenic vacuum water extraction device guarantees stable extraction conditions. Thus, this apparatus is a proper tool to be applied in water isotope research sciences.
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