Cryogenic Vacuum Distillation Research Articles

Effects of cryogenic vacuum distillation on the stable isotope ratios of soil water

Effects of cryogenic vacuum distillation on the stable isotope ratios of soil water

A simple greenhouse experiment to explore the effect of cryogenic water extraction for tracing plant source water

AbstractStable isotopes of water (2H and 18O) are useful tracers for determining root water uptake depths. In such studies, plant and soil water are extracted most commonly by cryogenic vacuum distillation. However, recent studies have suggested that cryogenic extraction conditions (extraction time, temperature, and vacuum) and soil physicochemical properties affect the isotopic composition of extracted soil water. Here, we perform a simple greenhouse trial with 2 plant species (Taraxacum officinale and Pelargonium spp.) in 2 soil types (clayey loam and sand) to test our ability to match plant water to its putative soil water source(s) by using different extraction conditions (30–240 min, 80–200 °C, 0.1 Pa). We irrigated plants with water of known isotopic composition, sampled root crowns and soils at 2 depths, and varied the cryogenic water extraction conditions.Our isotope results from the sandy soils were unaffected by cryogenic extraction conditions. In contrast, extraction parameters affected the isotope composition of waters recovered from clayey soil. This influenced the estimates of plant water sourcing, where δ2H and δ18O returned different results from each other. With higher extraction temperatures and longer extraction times, we gradually extracted more enriched soil water, which reflected the source water of both plant species. Our results imply that longer extraction times and temperatures for clayey soils are needed to reduce fractionation effects during the extraction procedure. Future studies should explore how these effects apply to natural clay‐rich soils as well as plant tissue isotope composition.

Non-destructive estimates of soil carbonic anhydrase activity and associated soil water oxygen isotope composition

Abstract. The contribution of photosynthesis and soil respiration to net land–atmosphere carbon dioxide (CO2) exchange can be estimated based on the differential influence of leaves and soils on budgets of the oxygen isotope composition (δ18O) of atmospheric CO2. To do so, the activity of carbonic anhydrases (CAs), a group of enzymes that catalyse the hydration of CO2 in soils and plants, needs to be understood. Measurements of soil CA activity typically involve the inversion of models describing the δ18O of CO2 fluxes to solve for the apparent, potentially catalysed, rate of CO2 hydration. This requires information about the δ18O of CO2 in isotopic equilibrium with soil water, typically obtained from destructive, depth-resolved sampling and extraction of soil water. In doing so, an assumption is made about the soil water pool that CO2 interacts with, which may bias estimates of CA activity if incorrect. Furthermore, this can represent a significant challenge in data collection given the potential for spatial and temporal variability in the δ18O of soil water and limited a priori information with respect to the appropriate sampling resolution and depth. We investigated whether we could circumvent this requirement by inferring the rate of CO2 hydration and the δ18O of soil water from the relationship between the δ18O of CO2 fluxes and the δ18O of CO2 at the soil surface measured at different ambient CO2 conditions. This approach was tested through laboratory incubations of air-dried soils that were re-wetted with three waters of different δ18O. Gas exchange measurements were made on these soils to estimate the rate of hydration and the δ18O of soil water, followed by soil water extraction to allow for comparison. Estimated rates of CO2 hydration were 6.8–14.6 times greater than the theoretical uncatalysed rate of hydration, indicating that CA were active in these soils. Importantly, these estimates were not significantly different among water treatments, suggesting that this represents a robust approach to assay the activity of CA in soil. As expected, estimates of the δ18O of the soil water that equilibrates with CO2 varied in response to alteration to the δ18O of soil water. However, these estimates were consistently more negative than the composition of the soil water extracted by cryogenic vacuum distillation at the end of the gas measurements with differences of up to −3.94 ‰ VSMOW–SLAP. These offsets suggest that, at least at lower water contents, CO2–H2O isotope equilibration primarily occurs with water pools that are bound to particle surfaces and are depleted in 18O compared to bulk soil water.

Cryogenic vacuum artifacts do not affect plant water‐uptake studies using stable isotope analysis

AbstractWater movement through the soil‐plant‐atmosphere continuum can be tracked through its hydrogen and oxygen isotopic composition. How the isotopic composition of water evolves as it moves through this continuum provides critical information on ecosystem hydrology and climate change. Cryogenic vacuum extraction is the most applied method to extract waters from soil and plant material for such studies. However, recent experiments where oven dried soils were spiked with a reference water suggest potential for these techniques to bias results. We present results from a greenhouse‐based plant water uptake and cryogenic vacuum distillation experiment using Salix viminalis cuttings. We tested the capacity for cryogenic vacuum extraction to recover irrigation water and the plant‐available water pool from 4 soils that were subject to continuous irrigation as would occur in nature. Results show that δ2H and δ18O values of extracted soil waters reflect those of irrigation water, but with some influence of evaporation that varied with differences in soil humic and clay content. This suggests that isotope effects observed in laboratory experiments with oven‐dried soils may not be relevant under natural conditions. Cryogenic vacuum extraction also recovered xylem water δ2H values that matched the δ2H values of extracted soil water but revealed small, consistent offsets between xylem and soil water δ18O values of 0.84 ± 1.13‰. Although these effects may not significantly bias water isotope sourcing applications, they do result in large extrapolation errors when estimating original source water isotope composition from extracted xylem waters using the back extrapolation to the global meteoric water line method.

Sample Enrichment for Bioanalytical Assessment of Disinfected Drinking Water: Concentrating the Polar, the Volatiles, and the Unknowns.

Enrichment methods used in sample preparation for the bioanalytical assessment of disinfected drinking water result in the loss of volatile and hydrophilic disinfection byproducts (DBPs) and hence likely tend to underestimate biological effects. We developed and evaluated methods that are compatible with bioassays, for extracting nonvolatile and volatile DBPs from chlorinated and chloraminated drinking water to minimize the loss of analytes. For nonvolatile DBPs, solid-phase extraction (SPE) with TELOS ENV as solid phase performed superior compared to ten other sorbents. SPE yielded >70% recovery of nonpurgeable adsorbable organic halogens (AOX). For volatile DBPs, cryogenic vacuum distillation performed unsatisfactorily. Purge and cold-trap with crushed ice serving as condensation nuclei achieved recoveries of 50-100% for trihalomethanes and haloacetonitriles and approximately 60-90% for purged AOX from tap water. We compared the purgeable versus the nonpurgeable fraction by combining purge-and-trap extraction with SPE. The purgeable DBP fraction enriched with the purge-and-trap method exerted a lower oxidative stress response in mammalian cells than the nonpurgeable DBPs enriched with SPE after purging, while contributions of both fractions to bacterial cytotoxicity was more variable. 37 quantified DBPs explained almost the entire AOX in the purge-and-trap extracts, but <16% in the SPE extracts demonstrating that the nonpurgeable fraction is dominated by unknown DBPs.

Rainwater use by irrigated cotton measured with stable isotopes of water

The natural rate of recharge for some groundwater systems, such as the Southern Ogallala Aquifer in the central United States, is smaller than the rate of annual withdrawals for irrigation. As aquifer depletion continues, efficient management of the water budget gains importance. Of interest is the use of rainwater by irrigated crops during the course of the growing season, as rain can account for an important amount of the water input in the semi-arid climate of the Texas High Plains. We tested the suitability of stable isotopes of water as a method to determine the source of water in the transpiration of field-grown cotton (Gossypium hirsutum L.) plants from either rain or irrigation-water. We selected this method because irrigation water from the Ogallala Aquifer has a stable isotopic signature that can either be enriched or depleted when compared to the isotopic signature of water from any rain event. Cotton petioles were sampled before two rain events of 33mm, and after every 2h for two days. The water in the cotton petioles was extracted using cryogenic vacuum distillation and was analyzed for its isotopic signature. The results showed a shift of 29% from −7 (‰) to −5 δ18O (‰), which is similar to the isotopic signature of the rainwater (−4.2 δ18O (‰)). These results suggest that it is possible to use water stable isotopes to differentiate between rainwater and irrigation transpired by cotton under field conditions.

Seasonal variations in depth of water uptake for a subtropical coniferous plantation subjected to drought in an East Asian monsoon region

Seasonal drought will become more intense and frequent in some regions due to global climate change, which may lead to significant changes in the competitive interactions and uptake depths of plant water sources. Based on δ18O and δD in xylem and soil water, we investigated the impacts of seasonal drought on plant water sources from July 2011 to October 2013 for a subtropical coniferous plantation in southeastern China. Our results indicated that the studied tree species of Pinus massoniana, Pinus elliottii and Cunninghamia lanceolata appeared to have inter-specific competition for water resources from similar depths. There was a switch of the major water source from shallow soil during the non-drought periods (July to October) to deep soil during the drought periods (November–June). Similar seasonal trend of water uptake was estimated by δ18O and δD. However, relative to the results of δD, water sources predicted by δ18O showed that trees seemed to derive more deep soil water during the drought periods and more shallow soil water during the non-drought periods. The differences of plant water source partitioning based on δ18O and δD were significant during both the drought and non-drought periods, which probably resulted from the artifacts of the cryogenic vacuum distillation and spectral contamination correction. These findings will have important implications for further studies when just one of the dual stable isotopes of δ18O and δD is applied.

Microwave extraction-isotope ratio infrared spectroscopy (ME-IRIS): a novel technique for rapid extraction and in-line analysis of δ18O and δ2H values of water in plants, soils and insects.

Traditionally, stable isotope analysis of plant and soil water has been a technically challenging, labour-intensive and time-consuming process. Here we describe a rapid single-step technique which combines Microwave Extraction with Isotope Ratio Infrared Spectroscopy (ME-IRIS). Plant, soil and insect water is extracted into a dry air stream by microwave irradiation within a sealed vessel. The water vapor thus produced is carried to a cooled condensation chamber, which controls the water vapor concentration and flow rate to the spectrometer. Integration of the isotope signals over the whole analytical cycle provides quantitative δ(18)O and δ(2) H values for the initial liquid water contained in the sample. Calibration is carried out by the analysis of water standards using the same apparatus. Analysis of leaf and soil water by cryogenic vacuum distillation and IRMS was used to validate the ME-IRIS data. Comparison with data obtained by cryogenic distillation and IRMS shows that the new technique provides accurate water isotope data for leaves from a range of field-grown tropical plant species. However, two exotic nursery plants were found to suffer from spectral interferences from co-extracted organic compounds. The precision for extracted leaf, stem, soil and insect water was typically better than ±0.3 ‰ for δ(18)O and ±2 ‰ for δ(2) H values, and better than ±0.1 ‰ for δ(18)O and ±1 ‰ for δ(2) H values when analyzing water standards. The effects of sample size, microwave power and duration and sample-to-sample memory on isotope values were assessed. ME-IRIS provides rapid and low-cost extraction and analysis of δ(18)O and δ(2) H values in plant, soil and insect water (≈10-15 min for samples yielding ≈ 0.3 mL of water). The technique can accommodate whole leaves of many plant species.

Validation and application of a cryogenic vacuum extraction system for soil and plant water extraction for isotope analysis

Abstract. Stable isotopic analysis of water in plant, soil, and hydrological studies often requires the extraction of water from plant or soil samples. Cryogenic vacuum extraction is one of the most widely used and accurate extraction methods to obtain such water samples. Here, we present a new design of a cryogenic vacuum extraction system with 18 extraction slots and an innovative mechanism to aerate the vacuum system after extraction. This mobile and extendable multi-port extraction system overcomes the bottleneck of time required for capturing unfractionated extracted water samples by providing the possibility to extract a larger number of samples per day simultaneously. The aeration system prevents the loss or mixture of water vapor during defrosting by purging every sample with high-purity nitrogen gas. A set of system functionality tests revealed that the extraction device guarantees stable extraction conditions with no changes in the isotopic composition of the extracted water samples. Surprisingly, extractions of dried and rehydrated soils showed significant differences of the isotopic composition of the added water and the extracts. This observation challenges the assumption that cryogenic extraction systems to fully extract soil water. Furthermore, in a plant water uptake study different results for hydrogen and oxygen isotope data were obtained, raising problems in the definition from which depths plants really take up water. Results query whether the well-established and widely used cryogenic vacuum distillation method can be used in a standard unified method of fixed extraction times as it is often done.

A direct and rapid leaf water extraction method for isotopic analysis

Isotopic measurements of leaf water have provided insights into a range of ecophysiological and biogeochemical processes, but require an extraction step which often constitutes the major analytical bottleneck in large-scale studies. Current standard procedures for leaf water analysis are based on cryogenic vacuum or azeotrophic distillation, and are laborious, require sophisticated distillation lines and the use of toxic materials. We report a rapid technique based on centrifugation/filtration of leaf samples pulverised in their original sampling tubes, using a specifically adapted, simple apparatus. The leaf water extracts produced are suitable for isotopic analysis via pyrolysis gas chromatography isotope ratio mass spectrometry (PYR/GC/IRMS). The new method was validated against cryogenic vacuum distillation and showed an overall accuracy of +/-0.5 per thousand (nine grouped comparisons, n = 110) over a range of 21 per thousand. Effects due to the presence of soluble carbohydrates were near the detection limits for most samples analysed, and these effects could be corrected for (the extracted soluble organics could also be used for isotopic analysis). The extraction time for a routine eight-sample subset was reduced from 4 h (cryogenic distillation) to 45 min, limited only by the size of the centrifuge(s) used. This method provides a rapid, low-cost and reliable alternative to conventional vacuum and other distillation methods that can alleviate current restrictions on ecosystem- and global-scale studies that require high-throughput leaf water isotopic analysis.

Water extraction times for plant and soil materials used in stable isotope analysis

Stable isotopic analysis of water for many ecological applications commonly requires extractions of water from dozens to hundreds of plant and soil samples. With recent advances in mass spectrometry, water extraction, rather than the isotopic analysis itself, is the bottleneck in sample processing. Using cryogenic vacuum distillation, we have created extraction timing curves to determine how much time (T(min)) is required to extract an unfractionated water sample. Our results indicated that T(min) values are 60 to 75 min for stems, 40 min for clay soils, 30 min for sandy soils and 20 to 30 min for leaves. While the extraction times reported here may allow for some reductions relative to times reported in the literature, the extraction process will continue to be a rate-limiting step in plant water analyses. Ultimately, technological advances eliminating the need for extraction are required to greatly increase throughput rates in water isotope analysis for ecological research.

Ecosystem Geography. Robert G. Bailey. Springer-Verlag, New York, NY, 1996, 204 pp., illus., folded maps, US $34.50, (paperback) ISBN 0-387-94586-5, US $69.95 (hardcover), ISBN 0-387-94354-4.

Seasonal drought will become more intense and frequent in some regions due to global climate change, which may lead to significant changes in the competitive interactions and uptake depths of plant water sources. Based on δ18O and δD in xylem and soil water, we investigated the impacts of seasonal drought on plant water sources from July 2011 to October 2013 for a subtropical coniferous plantation in southeastern China. Our results indicated that the studied tree species of Pinus massoniana, Pinus elliottii and Cunninghamia lanceolata appeared to have inter-specific competition for water resources from similar depths. There was a switch of the major water source from shallow soil during the non-drought periods (July to October) to deep soil during the drought periods (November–June). Similar seasonal trend of water uptake was estimated by δ18O and δD. However, relative to the results of δD, water sources predicted by δ18O showed that trees seemed to derive more deep soil water during the drought periods and more shallow soil water during the non-drought periods. The differences of plant water source partitioning based on δ18O and δD were significant during both the drought and non-drought periods, which probably resulted from the artifacts of the cryogenic vacuum distillation and spectral contamination correction. These findings will have important implications for further studies when just one of the dual stable isotopes of δ18O and δD is applied.

Comparison of the disposition of butadiene epoxides in Sprague–Dawley rats and B6C3F1 mice following a single and repeated exposures to 1,3-butadiene via inhalation

1,3-Butadiene (BD), a compound used extensively in the rubber industry, is a potent carcinogen in mice and a weak carcinogen in rats in chronic carcinogenicity bioassays. While many chemicals are known to alter their own metabolism after repeated exposures, the effect of exposure prior to BD on its in vivo metabolism has not been reported. The purpose of the present research was to examine the effect of repeated exposure to BD on tissue concentrations of two mutagenic BD metabolites, butadiene monoepoxide (BDO) and butadiene diepoxide (BDO2). Concentrations of BD epoxides were compared in several tissues of rats and mice following a single exposure or ten repeated exposures to a target concentration of 62.5 ppm BD. Female Sprague–Dawley rats and female B6C3F1 mice were exposed to BD for 6 h or 6 h×10 days. BDO and BDO2 were quantified in blood and several other tissues following preparation by cryogenic vacuum distillation and analysis by multidimensional gas chromatography–mass spectrometry. Blood and lung BDO concentrations did not differ significantly (P≤0.05) between the two exposure regimens in either species. Following multiple exposures to BD, BDO levels were 5- and 1.6-fold higher (P≤0.05) in mammary tissue and 2- and 1.4-fold higher in fat tissue of rats and mice, respectively, as compared with single exposures. BDO2 levels also increased in rat fat tissue following multiple exposures to BD. However, in mice, levels of this metabolite decreased by 15% in fat, by 28% in mammary tissue and by 34% in lung tissue following repeated exposures to BD. The finding that the mutagenic epoxide BDO, which is the precursor to the highly mutagenic BDO2, accumulates in rodent fat may be important in assessing the potential risk to humans from inhalation of BD.