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Voigt C, Vallet-Coulomb C, Piel C, Alexandre A. 17 O-excess and d-excess of atmospheric water vapor measured by cavity ring-down spectrometry: Evidence of a matrix effect and implication for the calibration procedure. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2022; 36:e9227. [PMID: 34845759 DOI: 10.1002/rcm.9227] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/21/2021] [Revised: 11/22/2021] [Accepted: 11/22/2021] [Indexed: 06/13/2023]
Abstract
RATIONALE Producing robust high-frequency time series of raw atmospheric water vapor isotope data using laser spectrometry requires accurate calibration. In particular, the chemical composition of the analyzed sample gas can cause isotope bias. This study assesses the matrix effect on calibrated δ17 O, δ18 O, δ2 H, 17 O-excess, and d-excess values of atmospheric water vapor. METHODS A Picarro L2140-i cavity ring-down spectrometer with an autosampler and a vaporizer is used to analyze δ17 O, δ18 O, δ2 H, 17 O-excess, and d-excess of two water standards. Isotope data obtained using synthetic air and dry ambient air as carrier gas at water mixing ratios ranging from 2000 to 30 000 ppmv are compared. Based on the results, atmospheric water vapor measurements are calibrated. The expected precision is estimated by Monte Carlo simulation. RESULTS The dry air source strongly impacts raw isotope values of the two water standards but has no effect on the mixing ratio dependency functions. When synthetic air is used, δ17 O, δ18 O, and 17 O-excess of calibrated atmospheric water vapor are overestimated by 0.6‰, 0.7‰, and 217 per meg, respectively, whereas δ2 H and d-excess are underestimated by 1.5‰ and 7.3‰. Optimum precisions for the calibrated δ17 O, δ18 O, δ2 H, 17 O-excess, and d-excess values and 12 min integration time are 0.02‰, 0.03‰, 0.4‰, 14 per meg, and 0.4‰, respectively. CONCLUSIONS Regarding the obtained results, recommendations for the calibration of atmospheric water vapor isotope measurements are presented. The necessity to use dry ambient air as dry air source when running the standards for calibration is pointed out as a prerequisite for accurate atmospheric water vapor 17 O-excess and d-excess measurements.
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Affiliation(s)
- Claudia Voigt
- Aix Marseille Univ, CNRS, IRD, INRAE, CEREGE, Aix-en-Provence, France
| | | | - Clément Piel
- ECOTRON Européen de Montpellier, UAR 3248, Centre National de la Recherche Scientifique (CNRS), Campus de Baillarguet, Montferrier-sur-Lez, France
| | - Anne Alexandre
- Aix Marseille Univ, CNRS, IRD, INRAE, CEREGE, Aix-en-Provence, France
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Maity A, Maithani S, Pal A, Pradhan M. Highresolution spectroscopic probing of ortho and para nuclear-spin isomers of heavy water in the gas phase. Chem Phys 2021. [DOI: 10.1016/j.chemphys.2020.111041] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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Mattei A, Barbecot F, Guillon S, Goblet P, Hélie JF, Meyzonnat G. Improved accuracy and precision of water stable isotope measurements using the direct vapour equilibration method. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2019; 33:1613-1622. [PMID: 31141839 DOI: 10.1002/rcm.8494] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/20/2019] [Revised: 05/20/2019] [Accepted: 05/22/2019] [Indexed: 06/09/2023]
Abstract
RATIONALE A method to measure the δ2 H and δ18 O composition of pore water in soil samples using direct vapour equilibration and laser spectrometry was first described in 2008, and was rapidly adopted. Here, we describe an improved setup to measure pore water δ2 H and δ18 O values through direct vapour equilibration with a laser spectrometer, combining a liquid and a vapour mode for water isotope analyses, and resulting in improved accuracy. METHODS We first tested new gas sampling bags as part of the equilibration protocol. Then, to assess measurement accuracy, vapour samples from equilibrated liquid waters of known isotope composition were measured in the liquid mode of the analyser using the new setup as well as the manufacturer's vapour mode. Various modes of preparing liquid water standards, namely equilibration, nebulisation, and vapourisation, were tested to determine the best calibration in terms of accuracy. Finally, the proposed modified liquid setup was validated by analysing water vapour equilibrated from soil pore water of a known composition. RESULTS The δ2 H and δ18 O measurements were found to be more accurate by the modified liquid mode than by the factory-setup vapour mode. The strong and non-linear dependence of measured δ2 H and δ18 O values on H2 O concentration in vapour mode, especially at concentrations equal to the vapour pressure saturation typically found in laboratories, is problematic for corrections. Regarding calibration and standards, the use of two equilibrated liquid water standards was found to best calibrate measurements in the modified liquid setup. Finally, the modified liquid mode setup and its calibration, as described here, were shown to be appropriate for soil pore water analysis. CONCLUSIONS The proposed modified setup results in more precise δ2 H and δ18 O soil pore water values than the usual protocols. An average standard deviation of 0.04‰ for δ18 O values and 0.3‰ for δ2 H values, based on 228 soil sample analyses, was obtained.
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Affiliation(s)
- Alexandra Mattei
- GEOTOP, Département des sciences de la Terre et de l'atmosphère, Université du Québec à Montréal, CP8888 succ. Centre-Ville, Montréal, QC, H3C 3P8, Canada
- MINES ParisTech, PSL Research University, Centre for Geosciences and Geoengineering, 35 rue Saint-Honoré, 77300, Fontainebleau, France
| | - Florent Barbecot
- GEOTOP, Département des sciences de la Terre et de l'atmosphère, Université du Québec à Montréal, CP8888 succ. Centre-Ville, Montréal, QC, H3C 3P8, Canada
| | - Sophie Guillon
- MINES ParisTech, PSL Research University, Centre for Geosciences and Geoengineering, 35 rue Saint-Honoré, 77300, Fontainebleau, France
| | - Patrick Goblet
- MINES ParisTech, PSL Research University, Centre for Geosciences and Geoengineering, 35 rue Saint-Honoré, 77300, Fontainebleau, France
| | - Jean-François Hélie
- GEOTOP, Département des sciences de la Terre et de l'atmosphère, Université du Québec à Montréal, CP8888 succ. Centre-Ville, Montréal, QC, H3C 3P8, Canada
| | - Guillaume Meyzonnat
- GEOTOP, Département des sciences de la Terre et de l'atmosphère, Université du Québec à Montréal, CP8888 succ. Centre-Ville, Montréal, QC, H3C 3P8, Canada
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Bonne JL, Behrens M, Meyer H, Kipfstuhl S, Rabe B, Schönicke L, Steen-Larsen HC, Werner M. Resolving the controls of water vapour isotopes in the Atlantic sector. Nat Commun 2019; 10:1632. [PMID: 30967532 PMCID: PMC6456600 DOI: 10.1038/s41467-019-09242-6] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2018] [Accepted: 02/27/2019] [Indexed: 11/25/2022] Open
Abstract
Stable water isotopes are employed as hydrological tracers to quantify the diverse implications of atmospheric moisture for climate. They are widely used as proxies for studying past climate changes, e.g., in isotope records from ice cores and speleothems. Here, we present a new isotopic dataset of both near-surface vapour and ocean surface water from the North Pole to Antarctica, continuously measured from a research vessel throughout the Atlantic and Arctic Oceans during a period of two years. Our observations contribute to a better understanding and modelling of water isotopic composition. The observations reveal that the vapour deuterium excess within the atmospheric boundary layer is not modulated by wind speed, contrary to the commonly used theory, but controlled by relative humidity and sea surface temperature only. In sea ice covered regions, the sublimation of deposited snow on sea ice is a key process controlling the local water vapour isotopic composition. Water isotope modelling is an important tool in climate reconstructions, but there remain gaps in our understanding of the effects upon oxygen and hydrogen isotope fractionation, and thus the source of the deposited signal. Here, the authors present a dataset assembled over two years that shows deuterium excess is controlled by humidity and sea surface temperature, and oxygen and hydrogen isotopes as well as deuterium excess are controlled by sublimation of snow in sea-ice regions.
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Affiliation(s)
- Jean-Louis Bonne
- Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, 27570, Germany.
| | - Melanie Behrens
- Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, 27570, Germany
| | - Hanno Meyer
- Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Potsdam, 14473, Germany
| | - Sepp Kipfstuhl
- Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, 27570, Germany
| | - Benjamin Rabe
- Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, 27570, Germany
| | - Lutz Schönicke
- Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Potsdam, 14473, Germany
| | - Hans Christian Steen-Larsen
- Geophysical Institute, University of Bergen and Bjerknes Centre for Climate Research, Bergen, 5020, Norway.,Center for Ice and Climate, Niels Bohr Institute, University of Copenhagen, Copenhagen, 2100, Denmark
| | - Martin Werner
- Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, 27570, Germany
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Cui J, Tian L, Gerlein-Safdi C, Qu D. The influence of memory, sample size effects, and filter paper material on online laser-based plant and soil water isotope measurements. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2017; 31:509-522. [PMID: 28072488 DOI: 10.1002/rcm.7824] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/29/2016] [Revised: 01/06/2017] [Accepted: 01/07/2017] [Indexed: 06/06/2023]
Abstract
RATIONALE The recent development of isotope ratio infrared spectroscopy (IRIS) was quickly followed by the addition of online extraction and analysis systems, making it faster and easier to measure soil and plant water isotopes. However, memory and sample size effects limit the efficiency and accuracy of these new setups. In response, this study presents a scheme dedicated to estimating and eliminating these two effects. METHODS Memory effect was determined by injecting two standard waters alternately. Each standard was injected nine times in a row and analyzed using induction module cavity ring-down spectroscopy (IM-CRDS). Memory coefficients were calculated using a new "multistage jump" algorithm. Sample size effects were evaluated by injecting water volumes ranging from 1 μL to 6 μL. Finally, the influence of cellulose filter paper on the isotopic measurements, the memory, and the sample size effect was evaluated by comparing it with glass filter paper. RESULTS Memory effects were detected for both δ18 O and δ2 H values, with the latter being stronger. Isotopic differences between replicates of the same plant or soil sample showed a clear decrease after memory correction. A small water volume effect was found only when the injected water volume was larger than 3 μL. However, while the correction method performed well for laboratory-made samples, it did not for field samples, due to the heterogeneity of the isotopic composition of the samples. Stronger memory and water volume effects were found for cellulose filter paper. CONCLUSIONS The memory coefficients and the water volume-isotope relationship improved the consistency and accuracy of both laboratory and field data. Our results indicate that cellulose filter paper may not be a suitable medium to measure standard waters and evaluate memory and water volume effects. Finally, a detailed correction and calibration protocol is suggested, along with notes on best practices to obtain good-quality IM-CRDS data. Copyright © 2017 John Wiley & Sons, Ltd.
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Affiliation(s)
- Jiangpeng Cui
- Key Laboratory of Tibetan Plateau Environment Change and Land Surface Processes, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing, 100101, China
- University of Chinese Academy of Sciences, Beijing, China
| | - Lide Tian
- Key Laboratory of Tibetan Plateau Environment Change and Land Surface Processes, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing, 100101, China
- CAS Centre for Excellence in Tibetan Plateau Earth Sciences, Beijing, 100101, China
| | - Cynthia Gerlein-Safdi
- Department of Civil and Environmental Engineering, Princeton University, Princeton, NJ, 08540, USA
| | - Dongmei Qu
- Key Laboratory of Tibetan Plateau Environment Change and Land Surface Processes, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing, 100101, China
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Benetti M, Steen-Larsen HC, Reverdin G, Sveinbjörnsdóttir ÁE, Aloisi G, Berkelhammer MB, Bourlès B, Bourras D, de Coetlogon G, Cosgrove A, Faber AK, Grelet J, Hansen SB, Johnson R, Legoff H, Martin N, Peters AJ, Popp TJ, Reynaud T, Winther M. Stable isotopes in the atmospheric marine boundary layer water vapour over the Atlantic Ocean, 2012-2015. Sci Data 2017; 4:160128. [PMID: 28094798 PMCID: PMC5240618 DOI: 10.1038/sdata.2016.128] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2016] [Accepted: 12/05/2016] [Indexed: 11/09/2022] Open
Abstract
The water vapour isotopic composition (1H216O, H218O and 1H2H16O) of the Atlantic marine boundary layer has been measured from 5 research vessels between 2012 and 2015. Using laser spectroscopy analysers, measurements have been carried out continuously on samples collected 10-20 meter above sea level. All the datasets have been carefully calibrated against the international VSMOW-SLAP scale following the same protocol to build a homogeneous dataset covering the Atlantic Ocean between 4°S to 63°N. In addition, standard meteorological variables have been measured continuously, including sea surface temperatures using calibrated Thermo-Salinograph for most cruises. All calibrated observations are provided with 15-minute resolution. We also provide 6-hourly data to allow easier comparisons with simulations from the isotope-enabled Global Circulation Models. In addition, backwards trajectories from the HYSPLIT model are supplied every 6-hours for the position of our measurements.
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Affiliation(s)
- Marion Benetti
- Institute of Earth Sciences, University of Iceland, Reykjavik, Iceland
- LOCEAN, Sorbonne Universités, UPMC/CNRS/IRD/MNHN, Paris, France
| | | | - Gilles Reverdin
- LOCEAN, Sorbonne Universités, UPMC/CNRS/IRD/MNHN, Paris, France
| | | | - Giovanni Aloisi
- LOCEAN, Sorbonne Universités, UPMC/CNRS/IRD/MNHN, Paris, France
| | - Max B. Berkelhammer
- Department of Earth and Environmental Sciences, University of Illinois, Chicago, Illinois, USA
| | - Bernard Bourlès
- LEGOS, UMR 5566 (University of Toulouse, CNES, CNRS, IRD, UPS), Institut de Recherche pour le Développement (IRD), CS 10070, 29280 Plouzané, France
| | - Denis Bourras
- LATMOS—IPSL, Universite Pierre et Marie Curie, Paris, France
- Aix-Marseille Université, CNRS/INSU, IRD, Mediterranean Institute of Oceanography (MIO), UM 110, 13288 Marseille, France
| | | | - Ann Cosgrove
- Department of Earth and Environmental Sciences, University of Illinois, Chicago, Illinois, USA
| | - Anne-Katrine Faber
- Centre for Ice and Climate, Niels Bohr Institute, University of Copenhagen, Denmark
| | - Jacques Grelet
- US191-Imago, Institut de Recherche pour le Développement (IRD), BP 70, 29280 Plouzané, France
| | - Steffen Bo Hansen
- Centre for Ice and Climate, Niels Bohr Institute, University of Copenhagen, Denmark
| | - Rod Johnson
- Bermuda Institute of Ocean Sciences, St George’s GE 01, Bermuda
| | - Hervé Legoff
- LOCEAN, Sorbonne Universités, UPMC/CNRS/IRD/MNHN, Paris, France
| | - Nicolas Martin
- LOCEAN, Sorbonne Universités, UPMC/CNRS/IRD/MNHN, Paris, France
| | | | - Trevor James Popp
- Centre for Ice and Climate, Niels Bohr Institute, University of Copenhagen, Denmark
| | - Thierry Reynaud
- IFREMER, UMR 6523 LOPS (CNRS/IFREMER/IRD/UBO), CS 10070, 29280 Plouzané, France
| | - Malte Winther
- Centre for Ice and Climate, Niels Bohr Institute, University of Copenhagen, Denmark
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Pratt DL, Lu M, Lee Barbour S, Jim Hendry M. An evaluation of materials and methods for vapour measurement of the isotopic composition of pore water in deep, unsaturated zones. ISOTOPES IN ENVIRONMENTAL AND HEALTH STUDIES 2016; 52:529-543. [PMID: 27002493 DOI: 10.1080/10256016.2016.1151423] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/30/2015] [Accepted: 01/08/2016] [Indexed: 06/05/2023]
Abstract
The development of in situ vapour sampling methods to measure δ(2)H and δ(18)O in pore water of deep, unsaturated soil profiles, including mine tailings and waste rock, is required to improve our ability to track water migration through these deposits. To develop appropriate field sampling methods, a laboratory study was first undertaken to evaluate potential materials and sampling methods to collect and analyse vapour samples from unsaturated mine waste. Field methods were developed based on these findings and tested at two mine sites using either on-site analyses with a portable isotope laser spectrometer or sample collection and storage prior to laboratory analyses. The field sites included a series of deep (>50 m) multiport profiles within a coal waste rock dump and open wells installed in a sand tailings dyke at an oil sands mine. Laboratory results show that memory effects in sample bags and tubing require 3-5 pore volumes of vapour flushing prior to sample collection and sample storage times are limited to 24 h. Field sampling highlighted a number of challenges including the need to correct for sample humidity and in situ temperature. Best results were obtained when a portable laser spectrometer was used to measure vapour samples in situ.
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Affiliation(s)
- Dyan L Pratt
- a Civil & Geological Engineering , University of Saskatchewan , Saskatoon , SK , Canada
| | - Mengna Lu
- a Civil & Geological Engineering , University of Saskatchewan , Saskatoon , SK , Canada
| | - S Lee Barbour
- a Civil & Geological Engineering , University of Saskatchewan , Saskatoon , SK , Canada
| | - M Jim Hendry
- b Geological Sciences , University of Saskatchewan , Saskatoon , SK , Canada
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Mitchell GW, Guglielmo CG, Hobson KA. Measurement of Whole-Body CO2 Production in Birds Using Real-Time Laser-Derived Measurements of Hydrogen (δ(2)H) and Oxygen (δ(18)O) Isotope Concentrations in Water Vapor from Breath. Physiol Biochem Zool 2015; 88:599-606. [PMID: 26658408 DOI: 10.1086/683013] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
The doubly labeled water (DLW) method is commonly used to measure energy expenditure in free-living wildlife and humans. However, DLW studies involving animals typically require three blood samples, which can affect behavior and well-being. Moreover, measurement of H (δ(2)H) and O (δ(18)O) isotope concentrations in H2O derived from blood using conventional isotope ratio mass spectrometry is technically demanding, time-consuming, and often expensive. A novel technique that would avoid these constraints is the real-time measurement of δ(2)H and δ(18)O in the H2O vapor of exhaled breath using cavity ring-down (CRD) spectrometry, provided that δ(2)H and δ(18)O from body H2O and breath were well correlated. Here, we conducted a validation study with CRD spectrometry involving five zebra finches (Taeniopygia guttata), five brown-headed cowbirds (Molothrus ater), and five European starlings (Sturnus vulgaris), where we compared δ(2)H, δ(18)O, and rCO2 (rate of CO2 production) estimates from breath with those from blood. Isotope concentrations from blood were validated by comparing dilution-space estimates with measurements of total body water (TBW) obtained from quantitative magnetic resonance. Isotope dilution-space estimates from δ(2)H and δ(18)O values in the blood were similar to and strongly correlated with TBW measurements (R(2) = 0.99). The (2)H and (18)O (ppm) in breath and blood were also highly correlated (R(2) = 0.99 and 0.98, respectively); however, isotope concentrations in breath were always less enriched than those in blood and slightly higher than expected, given assumed fractionation values between blood and breath. Overall, rCO2 measurements from breath were strongly correlated with those from the blood (R(2) = 0.90). We suggest that this technique will find wide application in studies of animal and human energetics in the field and laboratory. We also provide suggestions for ways this technique could be further improved.
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Affiliation(s)
- G W Mitchell
- Advanced Facility for Avian Research, Department of Biology, University of Western Ontario, London, Ontario, Canada; 2National Wildlife Research Centre, Wildlife Research Division, Environment Canada, Ottawa, Ontario, Canada; 3National Hydrology Research Centre, Wildlife Research Division, Environment Canada, Saskatoon, Saskatchewan, Canada
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Wong WW, Roberts SB, Racette SB, Das SK, Redman LM, Rochon J, Bhapkar MV, Clarke LL, Kraus WE. The doubly labeled water method produces highly reproducible longitudinal results in nutrition studies. J Nutr 2014; 144:777-83. [PMID: 24523488 PMCID: PMC3985832 DOI: 10.3945/jn.113.187823] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The doubly labeled water (DLW) method is considered the reference method for the measurement of energy expenditure under free-living conditions. However, the reproducibility of the DLW method in longitudinal studies is not well documented. This study was designed to evaluate the longitudinal reproducibility of the DLW method using 2 protocols developed and implemented in a multicenter clinical trial-the Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy (CALERIE). To document the longitudinal reproducibility of the DLW method, 2 protocols, 1 based on repeated analysis of dose dilutions over the course of the clinical trial (dose-dilution protocol) and 1 based on repeated but blinded analysis of randomly selected DLW studies (test-retest protocol), were carried out. The dose-dilution protocol showed that the theoretical fractional turnover rates for (2)H and (18)O and the difference between the 2 fractional turnover rates were reproducible to within 1% and 5%, respectively, over 4.5 y. The Bland-Altman pair-wise comparisons of the results generated from 50 test-retest DLW studies showed that the fractional turnover rates and isotope dilution spaces for (2)H and (18)O, and total energy expenditure, were highly reproducible over 2.4 y. Our results show that the DLW method is reproducible in longitudinal studies and confirm the validity of this method to measure energy expenditure, define energy intake prescriptions, and monitor adherence and body composition changes over the period of 2.5-4.4 y. The 2 protocols can be adopted by other laboratories to document the longitudinal reproducibility of their measurements to ensure the long-term outcomes of interest are meaningful biologically. This trial was registered at clinicaltrials.gov as NCT00427193.
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Affiliation(s)
- William W. Wong
- USDA/Agricultural Research Service Children’s Nutrition Research Center, Baylor College of Medicine, Houston, TX,To whom correspondence should be addressed. E-mail:
| | - Susan B. Roberts
- Jean Mayer USDA Human Nutrition Research Center on Aging, Tufts University, Boston, MA
| | | | - Sai Krupa Das
- Pennington Biomedical Research Center, Baton Rouge, LA; and
| | | | - James Rochon
- Duke Clinical Research Institute, Duke University, Durham, NC
| | | | - Lucinda L. Clarke
- Jean Mayer USDA Human Nutrition Research Center on Aging, Tufts University, Boston, MA
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