87Sr/86Sr measurements on marine sediments by inductively coupled plasma-mass spectrometry

The application of inductively coupled plasma-mass spectrometry (ICP-MS) is documented for the study of the strontium isotopic composition (⁸⁷Sr/⁸⁶Sr) in geological samples, i.e. in the marine lithic fraction of core sediments. Methods for the determination of the isotopic composition, its accuracy and precision are reported. The results obtained simultaneously on 11 samples by both ICP-MS and thermal ionization mass spectrometry (TIMS) reveal a very good correlation (r² = 0.955). Received: 24 February 1997 / Revised: 26 May 1997 / Accepted: 30 May 1997     

87Sr/86Sr measurements on marine sediments by inductively coupled plasma-mass spectrometry

The application of inductively coupled plasma-mass spectrometry (ICP-MS) is documented for the study of the strontium isotopic composition (⁸⁷Sr/⁸⁶Sr) in geological samples, i.e. in the marine lithic fraction of core sediments. Methods for the determination of the isotopic composition, its accuracy and precision are reported. The results obtained simultaneously on 11 samples by both ICP-MS and thermal ionization mass spectrometry (TIMS) reveal a very good correlation (r² = 0.955). Received: 24 February 1997 / Revised: 26 May 1997 / Accepted: 30 May 1997     

On the calibration of continuous,high‐precision δ18O and δ2H measurements using an off‐axis integrated cavity output spectrometer

The ¹⁸O and ²H of water vapor serve as powerful tracers of hydrological processes. The typical method for determining water vapor δ¹⁸O and δ²H involves cryogenic trapping and isotope ratio mass spectrometry. Even with recent technical advances, these methods cannot resolve vapor composition at high temporal resolutions. In recent years, a few groups have developed continuous laser absorption spectroscopy (LAS) approaches for measuring δ¹⁸O and δ²H which achieve accuracy levels similar to those of lab‐based mass spectrometry methods. Unfortunately, most LAS systems need cryogenic cooling and constant calibration to a reference gas, and have substantial power requirements, making them unsuitable for long‐term field deployment at remote field sites. A new method called Off‐Axis Integrated Cavity Output Spectroscopy (OA‐ICOS) has been developed which requires extremely low‐energy consumption and neither reference gas nor cryogenic cooling. In this report, we develop a relatively simple pumping system coupled to a dew point generator to calibrate an ICOS‐based instrument (Los Gatos Research Water Vapor Isotope Analyzer (WVIA) DLT‐100) under various pressures using liquid water with known isotopic signatures. Results show that the WVIA can be successfully calibrated using this customized system for different pressure settings, which ensure that this instrument can be combined with other gas‐sampling systems. The precisions of this instrument and the associated calibration method can reach ～0.08‰ for δ¹⁸O and ～0.4‰ for δ²H. Compared with conventional mass spectrometry and other LAS‐based methods, the OA‐ICOS technique provides a promising alternative tool for continuous water vapor isotopic measurements in field deployments. Copyright © 2009 John Wiley & Sons, Ltd.     

A dynamic soil chamber system coupled with a tunable diode laser for online measurements of δ13C, δ18O,and efflux rate of soil‐respired CO2

High frequency observations of the stable isotopic composition of CO₂ effluxes from soil have been sparse due in part to measurement challenges. We have developed an open‐system method that utilizes a flow‐through chamber coupled to a tunable diode laser (TDL) to quantify the rate of soil CO₂ efflux and its δ¹³C and δ¹⁸O values (δ¹³C_R and δ¹⁸O_R, respectively). We tested the method first in the laboratory using an artificial soil test column and then in a semi‐arid woodland. We found that the CO₂ efflux rates of 1.2 to 7.3 µmol m^?2 s^?1 measured by the chamber‐TDL system were similar to measurements made using the chamber and an infrared gas analyzer (IRGA) (R² = 0.99) and compared well with efflux rates generated from the soil test column (R² = 0.94). Measured δ¹³C and δ¹⁸O values of CO₂ efflux using the chamber‐TDL system at 2 min intervals were not significantly different from source air values across all efflux rates after accounting for diffusive enrichment. Field measurements during drought demonstrated a strong dependency of CO₂ efflux and isotopic composition on soil water content. Addition of water to the soil beneath the chamber resulted in average changes of +6.9 µmol m^?2 s^?1, ?5.0‰, and ?55.0‰ for soil CO₂ efflux, δ¹³C_R and δ¹⁸O_R, respectively. All three variables initiated responses within 2 min of water addition, with peak responses observed within 10 min for isotopes and 20 min for efflux. The observed δ¹⁸O_R was more enriched than predicted from temperature‐dependent H₂O‐CO₂ equilibration theory, similar to other recent observations of δ¹⁸O_R from dry soils (Wingate L, Seibt U, Maseyk K, Ogee J, Almeida P, Yakir D, Pereira JS, Mencuccini M. Global Change Biol. 2008; 14: 2178). The soil chamber coupled with the TDL was found to be an effective method for capturing soil CO₂ efflux and its stable isotope composition at high temporal frequency. Published in 2010 by John Wiley & Sons, Ltd.     

Online high‐precision δ2H and δ18O analysis in water by pyrolysis

A method for online simultaneous δ²H and δ¹⁸O analysis in water by high‐temperature conversion is presented. Water is injected by using a syringe into a high‐temperature carbon reactor and converted into H₂ and CO, which are separated by gas chromatography (GC) and carried by helium to the isotope ratio mass spectrometer for hydrogen and oxygen isotope analysis. A series of experiments was conducted to evaluate several issues such as sample size, temperature and memory effects. The δ²H and δ¹⁸O values in multiple water standards changed consistently as the reactor temperature increased from 1150 to 1480°C. The δ¹⁸O in water can be measured at a lower temperature (e.g. 1150°C) although the precision was relatively poor at temperatures <1300°C. Memory effects exist for δ²H and δ¹⁸O between two waters, and can be reduced (to <1%) with proper measures. The injection of different amounts of water may affect the isotope ratio results. For example, in contrast to small injections (100 nL or less) from small syringes (e.g. 1.2 µL), large injections (1 µL or more) from larger syringes (e.g. 10 µL) with dilution produced asymmetric peaks and shifts of isotope ratios, e.g. 4‰ for δ²H and 0.4‰ for δ¹⁸O, probably resulting from isotope fractionation during dilution via the ConFlo interface. This method can be used to analyze nanoliter samples of water (e.g. 30 nL) with good precision of 0.5‰ for δ²H and 0.1‰ for δ¹⁸O. This is important for geosciences; for instance, fluid inclusions in ancient minerals may be analyzed for δ²H and δ¹⁸O to help understand the formation environments. Copyright © 2009 John Wiley & Sons, Ltd.     

Simultaneous determination of δ15N and δ18O of N2O and δ13C of CH4 in nanomolar quantities from a single water sample

We have developed a rapid, sensitive, and automated analytical system to simultaneously determine the concentrations and stable isotopic compositions (δ¹⁵N, δ¹⁸O, and δ¹³C) of nanomolar quantities of nitrous oxide (N₂O) and methane (CH₄) in water, by combining continuous‐flow isotope‐ratio mass spectrometry and a helium‐sparging system to extract and purify the dissolved gases. Our system, which is composed of cold traps and a capillary gas chromatograph that use ultra‐pure helium as the carrier gas, achieves complete extraction of N₂O and CH₄ in a water sample and separation among N₂O, CH₄, and the other component gases. The flow path following exit from the gas chromatograph was periodically changed to pass the gases through the combustion furnace to convert CH₄ and the other hydrocarbons into CO₂, or to bypass the combustion furnace for the direct introduction of eluted N₂O into the mass spectrometer, for determining the stable isotopic compositions through monitoring the ions of m/z 44, 45, and 46 of CO and N₂O⁺. The analytical system can be operated automatically with sequential software programmed on a personal computer. Analytical precisions better than 0.2‰ and 0.3‰ and better than 1.4‰ and 2.6‰ were obtained for the δ¹⁵N and δ¹⁸O of N₂O, respectively, when more than 6.7 nmol and 0.2 nmol of N₂O, respectively, were injected. Simultaneously, analytical precisions better than 0.07‰ and 2.1‰ were obtained for the δ¹³C of CH₄ when more than 5.5 nmol and 0.02 nmol of CH₄, respectively, were injected. In this manner, we can simultaneously determine stable isotopic compositions of a 120 mL water sample with concentrations as low as 1.7 nmol/kg for N₂O and 0.2 nmol/kg for CH₄. Copyright © 2010 John Wiley & Sons, Ltd.     

Calibration of δ17O and δ18O of international measurement standards – VSMOW,VSMOW2, SLAP,and SLAP2

Due to exhaustion of the two primary calibration materials, Vienna Standard Mean Ocean Water (VSMOW) and Standard Light Antarctic Precipitation (SLAP), two replacement materials, VSMOW2 and SLAP2, were created with isotopic compositions as close as possible to the original standards in their D/H and ¹⁸O/¹⁶O ratios. Measurements of the δ¹⁷O composition constitute therefore an appropriate independent check of the achieved isotopic adjustment. Aliquots from ampoules of VSMOW, VSMOW2, SLAP, and SLAP2 were fluorinated by BrF₅ and analyzed using a dual‐inlet Delta E mass spectrometer. VSMOW2 and SLAP2 were found to be indistinguishable from VSMOW and SLAP, respectively, in their δ¹⁷O and δ¹⁸O values within measurement uncertainties. This result is a confirmation of the successful isotopic matching of VSMOW2 and SLAP2 to their predecessors. Further checks of the δ¹⁷O value of SLAP2 seem desirable. Copyright © 2010 John Wiley & Sons, Ltd.     

Minimization of sample requirement for δ18O in benzoic acid

The measurement of the oxygen stable isotope content in organic compounds has applications in many fields, ranging from paleoclimate reconstruction to forensics. Conventional High‐Temperature Conversion (HTC) techniques require >20 µg of O for a single δ¹⁸O measurement. Here we describe a system that converts the CO produced by HTC into CO₂ via reduction within a Ni‐furnace. This CO₂ is then concentrated cryogenically, and 'focused' into the isotope ratio mass spectrometry (IRMS) source using a low‐flow He carrier gas (6–8 mL/min). We report analyses of benzoic acid (C₇H₆O₂) reference materials that yielded precise δ¹⁸O measurement down to 1.3 µg of O, suggesting that our system could be used to decrease sample requirement for δ¹⁸O by more than an order of magnitude. Copyright © 2010 John Wiley & Sons, Ltd.     

Stationary properties of δE/δR

It is made clear that two different statements in the literature concerning energy derivatives are completely compatible by deriving them as two different interpretations of the same equation. Some other aspects of these results are also discussed.