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.     

Nicotine,acetanilide and urea multi‐level 2H‐, 13C‐ and 15N‐abundance reference materials for continuous‐flow isotope ratio mass spectrometry

Accurate determinations of stable isotope ratios require a calibration using at least two reference materials with different isotopic compositions to anchor the isotopic scale and compensate for differences in machine slope. Ideally, the δ values of these reference materials should bracket the isotopic range of samples with unknown δ values. While the practice of analyzing two isotopically distinct reference materials is common for water (VSMOW‐SLAP) and carbonates (NBS 19 and L‐SVEC), the lack of widely available organic reference materials with distinct isotopic composition has hindered the practice when analyzing organic materials by elemental analysis/isotope ratio mass spectrometry (EA‐IRMS). At present only L‐glutamic acids USGS40 and USGS41 satisfy these requirements for δ¹³C and δ¹⁵N, with the limitation that L‐glutamic acid is not suitable for analysis by gas chromatography (GC). We describe the development and quality testing of (i) four nicotine laboratory reference materials for on‐line (i.e. continuous flow) hydrogen reductive gas chromatography‐isotope ratio mass‐spectrometry (GC‐IRMS), (ii) five nicotines for oxidative C, N gas chromatography‐combustion‐isotope ratio mass‐spectrometry (GC‐C‐IRMS, or GC‐IRMS), and (iii) also three acetanilide and three urea reference materials for on‐line oxidative EA‐IRMS for C and N. Isotopic off‐line calibration against international stable isotope measurement standards at Indiana University adhered to the ‘principle of identical treatment’. The new reference materials cover the following isotopic ranges: δ²H_nicotine ?162 to ?45‰, δ¹³C_nicotine ?30.05 to +7.72‰, δ¹⁵N_nicotine ?6.03 to +33.62‰; δ¹⁵N_acetanilide +1.18 to +40.57‰; δ¹³C_urea ?34.13 to +11.71‰, δ¹⁵N_urea +0.26 to +40.61‰ (recommended δ values refer to calibration with NBS 19, L‐SVEC, IAEA‐N‐1, and IAEA‐N‐2). Nicotines fill a gap as the first organic nitrogen stable isotope reference materials for GC‐IRMS that are available with different δ¹⁵N values. Comparative δ¹³C and δ¹⁵N on‐line EA‐IRMS data from 14 volunteering laboratories document the usefulness and reliability of acetanilides and ureas as EA‐IRMS reference materials. Published in 2009 by John Wiley & Sons, Ltd.     

Inter-laboratory calibration of new silver orthophosphate comparison materials for the stable oxygen isotope analysis of phosphates

Stable oxygen isotope compositions (δ¹⁸O values) of two commercial and one synthesized silver orthophosphate reagents have been determined on the VSMOW scale. The analyses were carried out in three different laboratories: lab (1) applying off‐line oxygen extraction in the form of CO₂ which was analyzed on a dual inlet and triple collector isotope ratio mass spectrometer, while labs (2) and (3) employed an isotope ratio mass spectrometer coupled to a high‐temperature conversion/elemental analyzer (TC/EA) where Ag₃PO₄ samples were analyzed as CO in continuous flow mode. The δ¹⁸O values for the proposed new comparison materials were linked to the generally accepted δ¹⁸O values for Vennemann's TU‐1 and TU‐2 standards as well as for Ag₃PO₄ extracted from NBS120c. The weighted average δ¹⁸O_VSMOW values for the new comparison materials UMCS‐1, UMCS‐2 and AGPO‐SCRI were determined to be + 32.60 (± 0.12), + 19.40 (± 0.12) and + 14.58 (± 0.13)‰, respectively. Copyright © 2011 John Wiley & Sons, Ltd.     

Calcite‐CO2 mixed into CO2‐free air: a new CO2‐in‐air stable isotope reference material for the VPDB scale

In order to generate a reliable and long‐lasting stable isotope ratio standard for CO₂ in samples of clean air, CO₂ is liberated from well‐characterized carbonate material and mixed with CO₂‐free air. For this purpose a dedicated acid reaction and air mixing system (ARAMIS) was designed. In the system, CO₂ is generated by a conventional acid digestion of powdered carbonate. Evolved CO₂ gas is mixed and equilibrated with a prefabricated gas comprised of N₂, O₂, Ar, and N₂O at close to ambient air concentrations. Distribution into glass flasks is made stepwise in a highly controlled fashion. The isotopic composition, established on automated extraction/measurement systems, varied within very small margins of error appropriate for high‐precision air‐CO₂ work (about ±0.015‰ for δ¹³C and ±0.025‰ for δ¹⁸O). To establish a valid δ¹⁸O relation to the VPDB scale, the temperature dependence of the reaction between 25 and 47°C has been determined with a high level of precision. Using identical procedures, CO₂‐in‐air mixtures were generated from a selection of reference materials; (1) the material defining the VPDB isotope scale (NBS 19, δ¹³C = +1.95‰ and δ¹⁸O = ?2.2‰ exactly); (2) a local calcite similar in isotopic composition to NBS 19 (‘MAR‐J1’, δ¹³C = +1.97‰ and δ¹⁸O = ?2.02‰), and (3) a natural calcite with isotopic compositions closer to atmospheric values (‘OMC‐J1’, δ¹³C = ?4.24‰ and δ¹⁸O = ?8.71‰). To quantitatively control the extent of isotope‐scale contraction in the system during mass spectrometric measurement other available international and local carbonate reference materials (L‐SVEC, IAEA‐CO‐1, IAEA‐CO‐8, CAL‐1 and CAL‐2) were also processed. As a further control pure CO₂ reference gases (Narcis I and II, NIST‐RM 8563, GS19 and GS20) were mixed with CO₂‐free synthetic air. Independently, the pure CO₂ gases were measured on the dual inlet systems of the same mass spectrometers. The isotopic record of a large number of independent batches prepared over the course of several months is presented. In addition, the relationship with other implementations of the VPDB‐scale for CO₂‐in‐air (e.g. CG‐99, based on calibration of pure CO₂ gas) has been carefully established. The systematic high‐precision comparison of secondary carbonate and CO₂ reference materials covering a wide range in isotopic composition revealed that assigned δ‐values may be (slightly) in error. Measurements in this work deviate systematically from assigned values, roughly scaling with isotopic distance from NBS 19. This finding indicates that a scale contraction effect could have biased the consensus results. The observation also underlines the importance of cross‐contamination errors for high‐precision isotope ratio measurements. As a result of the experiments, a new standard reference material (SRM), which consists of two 5‐L glass flasks containing air at 1.6 bar and the CO₂ evolved from two different carbonate materials, is available for distribution. These ‘J‐RAS’ SRM flasks (‘Jena‐Reference Air Set’) are designed to serve as a high‐precision link to VPDB for improving inter‐laboratory comparability. a Copyright © 2005 John Wiley & Sons, Ltd.     

Micro‐scale (1.5 µm) sulphur isotope analysis of contemporary and early Archean pyrite

We present a method for in situ sulphur (S) isotopic analysis of significantly small areas (1.5 µm in diameter) in pyrite using secondary ion mass spectrometry (NanoSIMS) to interpret microbial sulphur metabolism in the early earth. We evaluated the precision and accuracy of S isotopic ratios obtained by this method using hydrothermal pyrite samples with homogeneous S isotopic ratios. The internal precision of the δ³⁴S value was 1.5‰ at the level of 1 sigma of standard error (named 1SE) for a single spot, while the external reproducibility was estimated to be 1.6‰ at the level of 1 sigma of standard deviation (named 1SD, n = 25). For each separate sample, the average δ³⁴S value was comparable with that measured by a conventional method, and the accuracy was better than 2.3‰. Consequently, the in situ method is sufficiently accurate and precise to detect the S isotopic variations of small sample of the pyrite (less than 20 µm) that occurs ubiquitously in ancient sedimentary rocks. This method was applied to measure the S isotopic distribution of pyrite within black chert fragments in early Archean sandstone. The pyrite had isotopic zoning with a ³⁴S‐depleted core and ³⁴S‐enriched rim, suggesting isotopic evolution of the source H₂S from ?15 to ?5‰. Production of H₂S by microbial sulphate reduction (MSR) in a closed system provides a possible explanation for both the ³⁴S‐depleted initial H₂S and the progressive increase in the δ³⁴S_H2S value. Although more extensive data are necessary to strengthen the explanation for the origin of the MSR, the results show that the S isotopic distribution within pyrite crystals may be a key tracer for MSR activity in the early earth. Copyright © 2010 John Wiley & Sons, Ltd.     

Improved online hydrogen isotope analysis of halite aqueous inclusions

We demonstrate an improved method based on continuous‐flow elemental analyser pyrolysis isotopic ratio mass spectrometry (CF‐EA‐PY‐IRMS) to measure the ²H/¹H ratios of water trapped in halite crystals. Two challenges to overcome are the low hydrogen concentration of samples (10‐50 μmol H₂·g^?1) and the high chloride concentration released when reacting halite in an elemental analyser. We describe an optimization procedure for determining the ²H/¹H ratio of this trapped water with an acceptable accuracy. This technique involves the use of a high‐temperature Cr reactor to quantitatively convert H₂O into H₂. The initial step was performed on halite crystals precipitated from a water reservoir where ²H/¹H ratios were monitored from its initial stage until the end of evaporation. The ²H/¹H isotopic analyses were automated online in continuous‐flow mode. Precision of the method was determined for those “synthetic” samples with hydrogen concentrations ranging from 0.2 to 0.5 wt%. ²H/¹H isotopic ratios of evaporating waters bracket the compositions of water inclusions. The formation of fluid inclusions is not instantaneous and records the isotopic signature of the residual waters across a time range during which the isotopic values of the water still evolve. This property explains why the δ²H_VSMOW standard deviation of ±5‰ (2σ) observed for 10‐mg aliquots of halite exceeds the instrumental error (about ±1.5‰ 2σ) determined on the basis of IAEA‐CH7, NBS 30, and NBS 22 references along with calibrated waters with and without added halite crystals. We also applied this method to Mesoproterozoic (1.4 Ga) and Neoproterozoic (0.8 Ga) halite samples with relatively low hydrogen concentrations (300‐1500 ppm). The measured δ²H_VSMOW values for Precambrian waters range from ?89‰ to ?54‰. We propose that this technique offers a new perspective and great potential for palaeoenvironmental reconstructions based on the ²H/¹H analyses of water trapped in halite.     

Novel silver‐tubing method for quantitative introduction of water into high‐temperature conversion systems for stable hydrogen and oxygen isotopic measurements

A new method to seal water in silver tubes for use in a TC/EA (thermal conversion/elemental analyzer) reduction unit using a semi‐automated sealing apparatus can yield reproducibilities (1 standard deviation) of δ²H and δ¹⁸O measurements of 1.0‰ and 0.06‰, respectively. These silver tubes containing reference waters may be preferred for the calibration of H‐ and O‐bearing materials analyzed with a TC/EA reduction unit. The new sealing apparatus employs a computer‐controlled stepping motor to produce silver tubes identical in length. The reproducibility of the mass of water sealed in tubes (in a range of 200–400 µg) can be as good as 1%. Approximately 99% of the sealed silver tubes are satisfactory (leak free). Although silver tubes sealed with reference waters are robust and can be shaken or heated to 110°C with no loss of integrity, they should not be frozen because the expansion during the phase transition of water to ice will break the cold seals and all the water will be lost. The tubes should be shipped in insulated containers. This new method eliminates air inclusions and isotopic fractionation of water associated with the loading of water into capsules using a syringe. The method is also more than an order of magnitude faster than preparing water samples in ordinary Ag capsules. Nevertheless, some laboratories may prefer loading water into silver capsules because expensive equipment is not needed, but users of this method are cautioned to apply the necessary corrections for evaporation, back exchange with laboratory atmospheric moisture, and blanks. Copyright © 2010 John Wiley & Sons, Ltd.     

Membrane permeation continuous‐flow isotope ratio mass spectrometry for on‐line carbon isotope ratio determination

Gaseous membrane permeation (MP) technologies have been combined with continuous‐flow isotope ratio mass spectrometry for on‐line δ¹³C measurements. The experimental setup of membrane permeation‐gas chromatography/combustion/isotope ratio mass spectrometry (MP‐GC/C/IRMS) quantitatively traps gas streams in membrane permeation experiments under steady‐state conditions and performs on‐line gas transfer into a GC/C/IRMS system. A commercial polydimethylsiloxane (PDMS) membrane sheet was used for the experiments. Laboratory tests using CO₂ demonstrate that the whole process does not fractionate the C isotopes of CO₂. Moreover, the δ¹³C values of CO₂ permeated on‐line give the same isotopic results as off‐line static dual‐inlet IRMS δ¹³C measurements. Formaldehyde generated from aqueous formaldehyde solutions has also been used as the feed gas for permeation experiments and on‐line δ¹³C determination. The feed‐formaldehyde δ¹³C value was pre‐determined by sampling the headspace of the thermostated aqueous formaldehyde solution. Comparison of the results obtained by headspace with those from direct aqueous formaldehyde injection confirms that the headspace sampling does not generate isotopic fractionation, but the permeated formaldehyde analyzed on‐line yields a ¹³C enrichment relative to the feed δ¹³C value, the isotopic fractionation being 1.0026 ± 0.0003. The δ¹³C values have been normalized using an adapted two‐point isotopic calibration for δ¹³C values ranging from ?42 to ?10‰. The MP‐GC/C/IRMS system allows the δ¹³C determination of formaldehyde without chemical derivatization or additional analytical imprecision. Copyright © 2009 John Wiley & Sons, Ltd.     

Offline oxygen isotope analysis of organic compounds with high N:O

Although the advantages of online δ¹⁸O analysis of organic compounds make its broad application desirable, researchers have encountered NO⁺ isobaric interference with CO⁺ at m/z 30 (e.g. ¹⁴N¹⁶O⁺, ¹²C¹⁸O⁺) when analyzing nitrogenous substrates. If the δ¹⁸O value of inter‐laboratory standards for substrates with high N:O value could be confirmed offline, these materials could be analyzed periodically and used to evaluate δ¹⁸O data produced online for nitrogenous unknowns. To this end, we present an offline method based on modifications of the methods of Schimmelmann and Deniro (Anal. Chem. 1985; 57: 2644) and Sauer and Sternberg (Anal. Chem. 1994; 66: 2409), whereby all the N₂ from the gas products of a chlorinated pyrolysis was eliminated, resulting in purified CO₂ for analysis via a dual‐inlet isotope ratio mass spectrometry system. We evaluated our method by comparing observed δ¹⁸O values with previously published or inter‐laboratory calibrated δ¹⁸O values for five nitrogen‐free working reference materials; finding isotopic agreement to within ±0.2‰ for SIGMA® cellulose, IAEA‐CH3 cellulose (C₆H₁₀O₅) and IAEA‐CH6 sucrose (C₁₂H₂₂O₁₁), and within ±1.8‰ for IAEA‐601 and IAEA‐602 benzoic acids (C₇H₆O₂). We also compared the δ¹⁸O values of IAEA‐CH3 cellulose and IAEA‐CH6 sucrose that was nitrogen‐'doped' with adenine (C₅H₅N₅), imidazole (C₃H₄N₂) and 2‐aminopyrimidine (C₄H₅N₃) with the undoped δ¹⁸O values for the same substrates; yielding isotopic agreement to within ±0.7‰. Finally, we provide an independent analysis of the δ¹⁸O value of IAEA‐600 caffeine (C₈H₁₀N₄O₂), previously characterized using online systems exclusively, and discuss the reasons for an average 1.4‰ enrichment in δ¹⁸O observed offline relative to the consensus online δ¹⁸O value. Copyright © 2010 John Wiley & Sons, Ltd.     

Hydrogen and oxygen isotopes of water from inclusions in minerals: design of a new crushing system and on‐line continuous‐flow isotope ratio mass spectrometric analysis

An analytical line for stable isotope analyses of water recovered from fluid inclusions in minerals was built and successfully tested. The line is based on the principle of continuous‐flow analysis of water via high‐temperature reduction on glassy carbon. It includes a custom‐designed set of high‐efficiency crushers and a cryo‐focusing cell. This paper provides details of the line design and discusses strategies for line conditioning and mitigation of memory effects. The line allows measurements of hydrogen and oxygen isotopes during a single acquisition. The precision of the analyses depends on the amount of water released from the inclusions. The best results are obtained for samples containing at least 0.1–0.2 µL (0.06–0.11 µmol) H₂O. For such samples precision is better than 1.5‰ for δD and 0.5‰ for δ¹⁸O (1σ). Smaller amounts of water can be measured but at lower precision. Analyses of modern calcite formed under stable conditions in a deep cave allowed assessment of the accuracy of the analyses. The δD values measured in fluid inclusions of this working standard match the δD value of the parent water, and the oxygen isotope values agree within ca. 0.5‰. This indicates that fluid inclusions trapped in calcite at near‐ambient temperatures (e.g. speleothems and low‐temperatures phreatic calcite) faithfully preserve the original isotopic composition of the parent waters. 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.     

Zu den Kristallstrukturen der Übergangsmetall(II)‐Dodekahydro‐closo‐Dodekaborat‐Hydrate Cu(H2O)5,5[B12H12]·2,5 H2O und Zn(H2O)6[B12H12]·6 H2O

On the Crystal Structures of the Transition‐Metal(II) Dodecahydro‐closo‐Dodecaborate Hydrates Cu(H₂O)_5.5[B₁₂H₁₂]·2.5 H₂O and Zn(H₂O)₆[B₁₂H₁₂]·6 H₂O By neutralization of an aqueous solution of the free acid (H₃O)₂[B₁₂H₁₂] with basic copper(II) carbonate or zinc carbonate, blue lath‐shaped single crystals of the octahydrate Cu[B₁₂H₁₂]·8 H₂O (≡ Cu(H₂O)_5.5[B₁₂H₁₂]·2.5 H₂O) and colourless face‐rich single crystals of the dodecahydrate Zn[B₁₂H₁₂]·12 H₂O (≡ Zn(H₂O)₆[B₁₂H₁₂]·6 H₂O) could be isolated after isothermic evaporation. Copper(II) dodecahydro‐closo‐dodecaborate octahydrate crystallizes at room temperature in the monoclinic system with the non‐centrosymmetric space group Pm (Cu(H₂O)_5.5[B₁₂H₁₂]·2.5 H₂O: a = 768.23(5), b = 1434.48(9), c = 777.31(5) pm, β = 90.894(6)°; Z = 2), whereas zinc dodecahydro‐closo‐dodecaborate dodecahydrate crystallizes cubic in the likewise non‐centrosymmetric space group F23 (Zn(H₂O)₆[B₁₂H₁₂]·6 H₂O: a = 1637.43(9) pm; Z = 8). The crystal structure of Cu(H₂O)_5.5[B₁₂H₁₂]·2.5 H₂O can be described as a monoclinic distortion variant of the CsCl‐type arrangement. As characteristic feature the formation of isolated [Cu₂(H₂O)₁₁]⁴⁺ units as a condensate of two corner‐linked Jahn‐Teller distorted [Cu(H₂O)₆]²⁺ octahedra via an oxygen atom of crystal water can be considered. Since “zeolitic” water of hydratation is also present, obviously both classical H–O^δ?···^+δH–O and non‐classical B–H^δ?···^+δH–O hydrogen bonds play a significant role for the stabilization of the structure. A direct coordinative influence of the quasi‐icosahedral [B₁₂H₁₂]^2? anions on the Cu²⁺ cations has not been determined. The zinc compound Zn(H₂O)₆[B₁₂H₁₂]·6 H₂O crystallizes in a NaTl‐type related structure. Two crystallographically different [Zn(H₂O)₆]²⁺ octahedra are present, which only differ in their relative orientation within the packing of the [B₁₂H₁₂]^2? anions. The stabilization of the crystal structure takes place mainly via H–O^δ?···^+δH–O hydrogen bonds, since again the hydrogen atoms of the [B₁₂H₁₂]^2? anions have no direct coordinative influence on the Zn²⁺ cations.     

Comprehensive inter‐laboratory calibration of reference materials for δ18O versus VSMOW using various on‐line high‐temperature conversion techniques

Internationally distributed organic and inorganic oxygen isotopic reference materials have been calibrated by six laboratories carrying out more than 5300 measurements using a variety of high‐temperature conversion techniques (HTC) a in an evaluation sponsored by the International Union of Pure and Applied Chemistry (IUPAC). To aid in the calibration of these reference materials, which span more than 125‰, an artificially enriched reference water (δ¹⁸O of +78.91‰) and two barium sulfates (one depleted and one enriched in ¹⁸O) were prepared and calibrated relative to VSMOW2 b and SLAP reference waters. These materials were used to calibrate the other isotopic reference materials in this study, which yielded:

2H/1H Ratio Analysis of Flavor Compounds by On‐Line Gas Chromatography Pyrolysis Isotope Ratio Mass Spectrometry (HRGC‐P‐IRMS): Benzaldehyde

Isotope ratio monitoring gas chromatography‐mass spectrometry of the ²H/¹H ratio by pyrolysis isotope ratio mass spectrometry (P‐IRMS) was used to analyze benzaldehyde originating from various sources. Based on the δ²H_SMOW value of an authentic reference sample determined with an elemental analyzer (EA), the range of reproducibility and linearity was checked. Correct (EA related) and reproducible data were obtained for sample amounts >0.6 μg benzaldehyde (on column). In another series of experiments, the influence of sample preparation, i. e. simultaneous distillation‐extraction (SDE) was found to be negligible. The following ranges of δ²H_SMOW values were determined for benzaldehyde using five types of samples, i. e. (i) synthetic (δ²H_SMOW –78 to –85‰, ex benzal chloride; +420 to +668‰, ex toluene) and ‘natural’ (including ‘ex‐cassia’) references (δ²H_SMOW –83 to –144‰); (ii) bitter almond oils (δ²H_SMOW –113 to –148‰); (iii) fruits (δ²H_SMOW –111 to –146‰); (iv) kernels (δ²H_SMOW –115 to –188‰); and (v) leaves (δ²H_SMOW –165 to –189‰).     

Zwei Dodekahydro‐closo‐Dodekaborate mit Lone‐Pair‐Kationen der 6. Periode im Vergleich: Tl2[B12H12] und Pb(H2O)3[B12H12]·3H2O

During the reaction of an aqueous solution of (H₃O)₂[B₁₂H₁₂] with Tl₂CO₃ anhydrous thallium(I) dodecahydro‐closo‐dodecaborate Tl₂[B₁₂H₁₂] is obtained as colorless, spherical single crystals. It crystallizes in the cubic system with the centrosymmetric space group Fm$\bar{3}$ (a = 1074.23(8) pm, Z = 4) in an anti‐CaF₂ type structure. Four quasi‐icosahedral [B₁₂H₁₂]^2– anions (d(B–B) = 180–181 pm, d(B–H) = 111 pm) exhibit coordinative influence on each Tl⁺ cation and provide a twelvefold coordination in the shape of a cuboctahedron (d(Tl–H) = 296 pm). There is no observable stereochemical activity of the non‐bonding electron pairs (6s² lone pairs) at the Tl⁺ cations. By neutralization of an aqueous solution of the acid (H₃O)₂[B₁₂H₁₂] with PbCO₃ and after isothermic evaporation colorless, plate‐like single crystals of lead(II) dodecahydro‐closo‐dodecaborate hexahydrate Pb(H₂O)₃[B₁₂H₁₂] · 3H₂O can be isolated. This compound crystallizes orthorhombically with the non‐centrosymmetric space group Pna2₁ (a = 1839.08(9), b = 1166.52(6), c = 717.27(4) pm, Z = 4). The crystal structure of Pb(H₂O)₃[B₁₂H₁₂] · 3H₂O is characterized as a layer‐like arrangement. The Pb²⁺ cations are coordinated in first sphere by only three oxygen atoms from water molecules (d(Pb–O) = 247–248 pm). But a coordinative influence of the [B₁₂H₁₂]^2– anions (d(B–B) = 173–181 pm, d(B–H) = 93–122 pm) on lead has to be stated, too, as three hydrogen atoms from three different hydroborate anions are attached to the Pb²⁺ cations (d(Pb–H) = 258–270 pm) completing their first‐sphere coordination number to six. These three oxygen and three hydrogen ligands are arranged as quite irregular polyhedron leaving enough space for a stereochemical lone‐pair activity (6sp) at each Pb²⁺ cation. Since additional intercalating water of hydration is present as well, both classical H–O^δ– ··· ^+δH–O‐ and unconventional B–H^δ– ··· ^+δH–O hydrogen bonds play a significant role in the stabilization of the entire crystal structure.     

Supramolecular architectures of succinates of 1‐hydroxypropan‐2‐aminium derivatives

Aminoalkanol and aroxyalkyl derivatives are known as potential anticonvulsants. Two new salts, namely bis{(R,S)‐N‐[2‐(2,6‐dimethylphenoxy)ethyl]‐1‐hydroxypropan‐2‐aminium} succinate ( 1s ), C₁₃H₂₂NO₂⁺·0.5C₄H₄O₄²⁻, and bis{(S)‐(+)‐N‐[2‐(2,6‐dimethylphenoxy)ethyl]‐1‐hydroxypropan‐2‐aminium} succinate ( 2s ), C₁₃H₂₂NO₂⁺·0.5C₄H₄O₄²⁻, have been prepared and characterized by single‐crystal X‐ray diffraction. The N atoms are protonated by proton transfer from succinic acid. Salt 1s crystallizes in the space group P2₁/n with one cation and half an anion in the asymmetric unit across an inversion centre, while ( 2s ) crystallizes in the space group P2₁ with four cations and two anions in the asymmetric unit. The hydroxy group of the cation of 1s is observed in two R/S disorder positions. The crystals of these two salts display similar supramolecular architectures (i.e. two‐dimensional networks), built mainly by intermolecular N⁺—H…O^δ− and O—H…O^δ− hydrogen bonds, where `δ−' represents a partial charge. The succinate anions are engaged in hydrogen bonds, not only with protonated N atoms, but also with hydroxy groups.     

Synthese und Kristallstruktur von Cadmium‐Dodekahydro‐closo‐Dodekaborat‐Hexahydrat,Cd(H2O)6[B12H12]

Synthesis and Crystal Structure of Cadmium Dodecahydro closo‐Dodecaborate Hexahydrate, Cd(H₂O)₆[B₁₂H₁₂] Through neutralization of the aqueous free acid (H₃O)₂[B₁₂H₁₂] with cadmium carbonate (CdCO₃) and after isothermic evaporation of the resulting solution, colourless lath‐shaped single crystals of Cd(H₂O)₆[B₁₂H₁₂] are obtained. Cadmium dodecahydro closo‐dodecaborate hexahydrate crystallizes at room temperature in the monoclinic system (space group: C2/m) with the lattice constants a = 1413.42(9), b = 1439.57(9), c = 749.21(5) pm and β = 97.232(4)° (Z = 4). The crystal structure of Cd(H₂O)₆[B₁₂H₁₂] can be regarded as a monoclinic distortion variant of the CsCl‐type structure. Two crystallographically different [Cd(H₂O)₆]²⁺ octahedra (d(Cd–O) = 227–230 pm) are present which only differ in their relative orientation. The intramolecular bond lengths for the quasi‐icosahedral [B₁₂H₁₂]^2? cluster anions range in the intervals usually found for dodecahydro closo‐dodecaborates (d(B–B) = 177–179 pm, d(B–H) = 103–116 pm). The hydrogen atoms of the [B₁₂H₁₂]^2? clusters have no direct coordinative influence on the Cd²⁺ cations. Due to the fact that no “zeolitic” crystal water molecules are present, a stabilization of the lattice takes place mainly via the B–H^δ?···^+δH–O hydrogen bonds.     

Determination of the stable carbon isotopic compositions of 2‐methyltetrols in ambient aerosols from the Changbai Mountains

Isoprene is one of the most important non‐methane hydrocarbons (NMHCs) in the troposphere: it is a significant precursor of O₃ and it affects the oxidative state of the atmosphere. The diastereoisomeric 2‐methyltetrols, 2‐methylthreitol and 2‐methylerythritol, are marker compounds of the photooxidation products of atmospheric isoprene. In order to obtain valuable information on the δ¹³C value of isoprene in the atmosphere, the stable carbon isotopic compositions of the 2‐methyltetrols in ambient aerosols were investigated. The 2‐methyltetrols were extracted from filter samples and derivatized with methylboronic acid, and the δ¹³C values of the methylboronate derivatives were determined by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS). The δ¹³C values of the 2‐methyltetrols were then calculated through a simple mass balance equation between the 2‐methyltetrols, methylboronic acid and the methylboronates. The δ¹³C values of the 2‐methyltetrols in aerosol samples collected at the Changbai Mountain Nature Reserves in eastern China were found to be ?24.66 ± 0.90‰ and ?24.53 ± 1.08‰ for 2‐methylerythritol and 2‐methylthreitol, respectively. Based on the measured isotopic composition of the 2‐methyltetrols, the average δ¹³C value of atmospheric isoprene is inferred to be close to or slightly heavier than ?24.66‰ at the collection site during the sampling period. Copyright © 2010 John Wiley & Sons, Ltd.     

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.     

Demonstration of high‐precision continuous measurements of water vapor isotopologues in laboratory and remote field deployments using wavelength‐scanned cavity ring‐down spectroscopy (WS‐CRDS) technology

This study demonstrates the application of Wavelength‐Scanned Cavity Ring‐Down Spectroscopy (WS‐CRDS) technology which is used to measure the stable isotopic composition of water. This isotopic water analyzer incorporates an evaporator system that allows liquid water as well as water vapor to be measured with high precision. The analyzer can measure HO, HO and HD¹⁶O content of the water sample simultaneously. The results of a laboratory test and two field trials with this analyzer are described. The results of these trials show that the isotopic water analyzer gives precise, accurate measurements with little or no instrument drift for the two most common isotopologues of water. In the laboratory the analyzer has a precision of 0.5 per mil for δD and 0.1 per mil for δ¹⁸O which is similar to the precision obtained by laboratory‐based isotope ratio mass spectrometers. In the field, when measuring vapor samples, the analyzer has a precision of 1.0 per mil for δD and 0.2 per mil for δ¹⁸O. These results demonstrate that the isotopic water analyzer is a powerful tool that is appropriate for use in a wide range of applications and environments. Copyright © 2009 John Wiley & Sons, Ltd.