Discrepancies between isotope ratio infrared spectroscopy and isotope ratio mass spectrometry for the stable isotope analysis of plant and soil waters (original) (raw)
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Isotope-ratio infrared spectroscopy: a reliable tool for the investigation of plant-water sources?
The New phytologist, 2015
Stable isotopes are extensively used as tracers for the study of plant-water sources. Isotope-ratio infrared spectroscopy (IRIS) offers a cheaper alternative to isotope-ratio mass spectroscopy (IRMS), but its use in studying plant and soil water is limited by the spectral interference caused by organic contaminants. Here, we examine two approaches to cope with contaminated samples in IRIS: on-line oxidation of organic compounds (MCM) and post-processing correction. We assessed these methods compared to IRMS across 136 samples of xylem and soil water, and a set of ethanol- and methanol-water mixtures. A post-processing correction significantly improved IRIS accuracy in both natural samples and alcohol dilutions, being effective with concentrations up to 8% of ethanol and 0.4% of methanol. MCM outperformed the post-processing correction in removing methanol interference, but did not effectively remove interference for high concentrations of ethanol. By using both approaches, IRIS can ...
Previous studies have demonstrated the potential for large errors to occur when analyzing waters containing organic contaminants using isotope ratio infrared spectroscopy (IRIS). In an attempt to address this problem, IRIS manufacturers now provide post-processing spectral analysis software capable of identifying samples with the types of spectral interference that compromises their stable isotope analysis. Here we report two independent tests of this post-processing spectral analysis software on two IRIS systems,OA-ICOS (Los Gatos Research Inc.) andWS-CRDS (Picarro Inc.). Following a similar methodology to a previous study, we cryogenically extracted plant leaf water and soil water and measured the d2H and d18O values of identical samples by isotope ratio mass spectrometry (IRMS) and IRIS. As an additional test, we analyzed plant stem waters and tap waters by IRMS and IRIS in an independent laboratory. For all tests we assumed that the IRMS value represented the “true“ value against which we could compare the stable isotope results from the IRIS methods. Samples showing significant deviations from the IRMS value (>2s) were considered to be contaminated and representative of spectral interference in the IRIS measurement. Over the two studies, 83% of plant species were considered contaminated on OA-ICOS and 58% on WS-CRDS. Post-analysis, spectra were analyzed using the manufacturer’s spectral analysis software, in order to see if the software correctly identified contaminated samples. In our tests the software performed well, identifying all the samples with major errors. However, some false negatives indicate that user evaluation and testing of the software are necessary. Repeat sampling of plants showed considerable variation in the discrepancies between IRIS and IRMS. As such, we recommend that spectral analysis of IRIS data must be incorporated into standard post-processing routines. Furthermore, we suggest that the results from spectral analysis be included when reporting stable isotope data from IRIS. Copyright # 2011 John Wiley & Sons, Ltd.
Isotope ratio infrared spectroscopy analysis of water samples without memory effects
Rapid Communications in Mass Spectrometry, 2021
RationaleSince their introduction more than a decade ago, isotope ratio infrared spectroscopy (IRIS) systems have rapidly become the standard for oxygen (δ18O) and hydrogen (δ2H) isotope analysis of water samples. An important disadvantage of IRIS systems is the well‐documented sample‐to‐sample memory effect, which requires each sample to be analyzed multiple times before the desired accuracy is reached, lengthening analysis times and driving up the costs of analyses.MethodsWe present an adapted set‐up and calculation protocol for fully automated analysis of water samples using a Picarro L2140‐i cavity ring‐down spectroscopy instrument. The adaptation removes memory effects by use of a continuously moisturized nitrogen carrier gas. Water samples of 0.5 μL are measured on top of the water vapor background, after which isotope ratios are calculated by subtraction of the background from the sample peaks.ResultsWith this new technique, single injections of water samples have internal pr...
Rapid Communications in Mass Spectrometry, 2011
The stable isotopes of water (hydrogen and oxygen isotopes) are of utmost interest in ecology and the geosciences. In many cases water has to be extracted directly from a matrix such as soil or plant tissue before isotopes can be analyzed by mass spectrometry. Currently, the most widely used technique for water is cryogenic vacuum extraction. We present a simple and inexpensive modification of this method and document tests conducted with soils of various grain size and tree core replicates taken on four occasions during 2010. The accuracies for sandy soils are between 0.4% and 3% over a range of 21% and 165% for d 18 O and d 2 H, respectively. Spiking tests with water of known isotope composition were conducted with soil and tree core samples; they indicate reliable precision after an extraction time of 15 min for sandy soils. For clayey soils and tree cores, the deviations were up to 0.63% and 4.7% for d 18 O and d 2 H, respectively. This indicates either that the extraction time should be extended or that mechanisms different from Rayleigh fractionation play a role. The modified protocol allows a fast and reliable extraction of large numbers of water samples from soil and plant material in preparation for stable isotope analyses.
Application of Stable Isotope Analysis in Water Quality Studies
2015
Surface and groundwater contamination is a special concern worldwide due to its impact in drinking water and particularly in human health. In the north of Chile, water supply is a sensitive issue, due to the water resource scarcity (arid zone). In this region groundwater is the main component of water resources and due to its importance it requires a proper preservation of its quality, without compromising its use by the different users involved. When groundwater has been contaminated, the most important aspects for assessing the causes and possible solutions are the identification of the polluters and the allocation of contaminant sources. Stable isotopes are one of the most useful tools that have been used in studies of water resources in establishing causes of contamination (fingerprinting) and the sources that are affecting the water quality. Stable isotopes have been used in several researches in Chile, highlighting its application in mining and agriculture settings. Industrial...
Interlaboratory comparison of methods to determine the stable isotope composition of soil water
Chemical geology, 1994
This paper presents results of an interlaboratory comparison of the effects of different techniques for extracting soil water on its measured 2H and ~sO composition. In the comparison, four soils (a sand, a gypseous sand, and a clay soil at high and low water contents) were prepared and distributed to fourteen laboratories. Water was then extracted from these samples and analysed using each laboratory's standard method. A number of verification procedures was used to ensure that the experiment was truly a comparison of extraction techniques and that reported variations were not due to sample preparation, transport or measurement. The extraction techniques used included azeotropic, vacuum and microdistillation methods. The results show a large variation between laboratories in the isotopic composition of the water extracted (of up to 300/00 for 2H and 3.40/00 for 180). The variation increased as the water content of the soil decreased and was greater for clays than sand at comparable soil matric suctions. The ~-value obtained was correlated with the final extraction temperature, with incomplete extraction being the most likely cause for the variation. The study highlights the need to develop standard protocols for the extraction of water from soils for isotopic analysis.
Clinical Chemistry and Laboratory Medicine, 1993
A fast and easy method is described which uses Fourier transform infrared spectroscopy (FT-IR) to measure the Ή/ 2 !! ratio of aqueous samples of less than 100 μΐ with high precision (+ 0.2-0.5% in the range of 89 to 2680 μΐ/ΐ). Using a thermostat-controlled CaF 2 cell, low resolution absorption specta (8 cm"" 1) are measured. The integral of absorption in the range of 2600 and 2460 cm" 1 (O 2 H vibration) is used to analyse the 2 H content of the sample. For measurements at low enrichment five standards are used (SLAP: 89.00 μΐ/ΐ, GISP: 126.3 μΐ/ΐ, V-SMOW: 156.0 μΐ/ΐ, all from the International Atomic Energy Agency, Vienna, Austria, standard 1: 183.3 μΐ/ΐ, standard 2: 222.5 μΐ/ΐ, both prepared by weighing and controlled by isotope ratio mass Spectrometry (IR-MS)). For measurements at high enrichment three standards are used (standard 2: 222.5 μΐ/ΐ, standard 3: 1323 μΐ/ΐ, standard 4: 2680 μΐ/ΐ, all prepared by weighing and controlled by IR-MS). Measured and reported 2 H concentrations coincide very well, two samples for quality control (145 and 1612 μΐ/ΐ) were measured with a precision of 0.3 and 0.4% corresponding to + 0.5 and 5.9 μΐ/ΐ.
A statistical analysis of IRMS and CRDS methods in isotopic ratios of 2H/1H and 18O/16O in water
SN Applied Sciences
Quantitative information about the variation in natural isotopic abundances in water is of great importance in a variety of fields. Due to the wide range of applications and types of samples, it is necessary that isotopic analyses have precision, accuracy and reproducibility. The present study compares the techniques of cavity ring-down spectroscopy (CRDS) and isotope-ratio mass spectrometry (IRMS) for the determination of the isotopic ratios of 2 H/ 1 H and 18 O/ 16 O in water in the two secondary standards, denoted PB3 and PB4, and in a certified material, GISP, Greenland Ice Sheet Precipitation, used as a quality tester of such measurements. The traditional method for measuring isotopic ratios is IRMS. Because of the nature of the molecule, the samples are not introduced directly into the mass spectrometer. Instead, the water is chemically converted to CO 2 and H 2. The other technique, CRDS, is a system of laser absorption that has great potential for the detection of atomic and molecular species with high sensitivity by measuring the light absorption ratio as a function of time, confined within an optical cavity of high finesse. In this technique, the water sample is converted into steam without undergoing conversion processes. Parametric (test T) and nonparametric (Wilcoxon) statistical tests were performed to compare the results obtained in the system, and CRDS and IRMS are from the same population. The values of the isotopic abundances of the two secondary standards [PB3, δD = − 1.9 ± 0.4 (‰) and δ 18 O = − 2.19 ± 0.24 (‰) and PB4, δ 2 H = − 71.4 ± 0.4 (‰) and δ 18 O = − 10.08 ± 0.19 (‰)] were determined with accuracy. For the certified standard GISP, values of δ 2 H = − 189.3 ± 0.5 (‰) and δ 18 O = − 24.69 ± 0.20 (‰) were obtained. Both techniques have factors that interfere with the accuracy of the measurements and require corrections. Comparing the results revealed that there was a greater accuracy for measurements with CRDS and greater precision for IRMS. However, the results are within the tolerance range of 0.2‰ for δ 18 O and 2.0‰ for δ 2 H in isotope hydrology.
Rapid communications in mass spectrometry : RCM, 2014
RATIONALE: Traditionally, stable isotope analysis of plant and soil water has been a technically challenging, labourintensive and time-consuming process. Here we describe a rapid single-step technique which combines Microwave Extraction with Isotope Ratio Infrared Spectroscopy (ME-IRIS). METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.