The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Richard E Russo - One of the best experts on this subject based on the ideXlab platform.
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advancing the analytical capabilities of laser ablation molecular isotopic spectrometry for boron isotopic analysis
Spectrochimica Acta Part B: Atomic Spectroscopy, 2014Co-Authors: Xianglei Mao, Arnab Sarka, Richard E RussoAbstract:Abstract Laser ablation molecular isotopic spectrometry (LAMIS) recently has been investigated for analysis of the boron isotopic composition in ambient air at atmospheric pressure. The initial precision of 100–400‰ (2σ) for the 10 B/ 11 B isotopic ratio was less than results obtained from other analytical methods like TIMS or ICP–MS. This paper describes how accuracy and precision for boron isotopic ratio using LAMIS can be improved to the few per mil level. Several optimization procedures, viz., spectral region of analysis, effect of flicker noise from matrix, spectral normalization and pre-treatment procedures, were studied. This paper reports a precision of 9‰ (2σ) for the 10 B/ 11 B ratio using alternative spectral normalization and pre-treatment procedures.
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laser ablation molecular isotopic spectrometry parameter influence on boron isotope measurements
Spectrochimica Acta Part B: Atomic Spectroscopy, 2011Co-Authors: Xianglei Mao, Alexander A Bolshakov, Dale L Perry, Osman Sorkhabi, Richard E RussoAbstract:Abstract Laser Ablation Molecular Isotopic Spectrometry (LAMIS) was recently reported for optical isotopic analysis of condensed samples in ambient air and at ambient pressure. LAMIS utilizes molecular emissions which exhibit larger isotopic spectral shits than in atomic transitions. For boron monoxide 10 BO and 11 BO, the isotopic shifts extend from 114 cm −1 (0.74 nm) to 145–238 cm −1 (5–8 nm) at the B 2 Σ + ( v = 0) → X 2 Σ + ( v = 2) and A 2 Π i ( v = 0) → X 2 Σ + ( v = 3) transitions, respectively. These molecular isotopic shifts are over two orders of magnitude larger than the maximum isotopic shift of approximately 0.6 cm −1 in atomic boron. This paper describes how boron isotope abundance can be quantitatively determined using LAMIS and how atomic, ionic, and molecular optical emission develops in a plasma emanating from laser ablation of solid samples with various boron isotopic composition. We demonstrate that requirements for spectral resolution of the measurement system can be significantly relaxed when the isotopic abundance ratio is determined using chemometric analysis of spectra. Sensitivity can be improved by using a second slightly delayed laser pulse arriving into an expanding plume created by the first ablation pulse.
Xianglei Mao - One of the best experts on this subject based on the ideXlab platform.
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advancing the analytical capabilities of laser ablation molecular isotopic spectrometry for boron isotopic analysis
Spectrochimica Acta Part B: Atomic Spectroscopy, 2014Co-Authors: Xianglei Mao, Arnab Sarka, Richard E RussoAbstract:Abstract Laser ablation molecular isotopic spectrometry (LAMIS) recently has been investigated for analysis of the boron isotopic composition in ambient air at atmospheric pressure. The initial precision of 100–400‰ (2σ) for the 10 B/ 11 B isotopic ratio was less than results obtained from other analytical methods like TIMS or ICP–MS. This paper describes how accuracy and precision for boron isotopic ratio using LAMIS can be improved to the few per mil level. Several optimization procedures, viz., spectral region of analysis, effect of flicker noise from matrix, spectral normalization and pre-treatment procedures, were studied. This paper reports a precision of 9‰ (2σ) for the 10 B/ 11 B ratio using alternative spectral normalization and pre-treatment procedures.
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laser ablation molecular isotopic spectrometry parameter influence on boron isotope measurements
Spectrochimica Acta Part B: Atomic Spectroscopy, 2011Co-Authors: Xianglei Mao, Alexander A Bolshakov, Dale L Perry, Osman Sorkhabi, Richard E RussoAbstract:Abstract Laser Ablation Molecular Isotopic Spectrometry (LAMIS) was recently reported for optical isotopic analysis of condensed samples in ambient air and at ambient pressure. LAMIS utilizes molecular emissions which exhibit larger isotopic spectral shits than in atomic transitions. For boron monoxide 10 BO and 11 BO, the isotopic shifts extend from 114 cm −1 (0.74 nm) to 145–238 cm −1 (5–8 nm) at the B 2 Σ + ( v = 0) → X 2 Σ + ( v = 2) and A 2 Π i ( v = 0) → X 2 Σ + ( v = 3) transitions, respectively. These molecular isotopic shifts are over two orders of magnitude larger than the maximum isotopic shift of approximately 0.6 cm −1 in atomic boron. This paper describes how boron isotope abundance can be quantitatively determined using LAMIS and how atomic, ionic, and molecular optical emission develops in a plasma emanating from laser ablation of solid samples with various boron isotopic composition. We demonstrate that requirements for spectral resolution of the measurement system can be significantly relaxed when the isotopic abundance ratio is determined using chemometric analysis of spectra. Sensitivity can be improved by using a second slightly delayed laser pulse arriving into an expanding plume created by the first ablation pulse.
David L. Bryce - One of the best experts on this subject based on the ideXlab platform.
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spying on the boron boron triple bond using spin spin coupling measured from 11b solid state nmr spectroscopy
Chemical Science, 2015Co-Authors: Frederic A Perras, William C Ewing, Theresa Dellermann, Julian Bohnke, Stefan Ullrich, Thomas Schafer, Holger Braunschweig, David L. BryceAbstract:There is currently tremendous interest in the previously documented example of a stable species exhibiting a boron–boron triple bond (Science, 2012, 336, 1420). Notably, it has recently been stated using arguments based on force constants that this diboryne may not, in reality, feature a boron–boron triple bond. Here, we use advanced solid-state NMR and computational methodology in order to directly probe the orbitals involved in multiple boron–boron bonds experimentally via analysis of 11B–11B spin–spin (J) coupling constants. Computationally, the mechanism responsible for the boron–boron spin–spin coupling in these species is found to be analogous to that for the case of multiply-bonded carbon atoms. The trend in reduced J coupling constants for diborenes and a diboryne, measured experimentally, is in agreement with that known for alkenes and alkynes. This experimental probe of the electronic structure of the boron–boron multiple bond provides strong evidence supporting the originally proposed nature of the bonds in the diboryne and diborenes, and demonstrates that the orbitals involved in boron–boron bonding are equivalent to those well known to construct the multiple bonds between other second-row elements such as carbon and nitrogen.
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A Solid-State 11B NMR and Computational Study of Boron Electric Field Gradient and Chemical Shift Tensors in Boronic Acids and Boronic Esters
2015Co-Authors: Joseph W E Weiss, David L. BryceAbstract:The results of a solid-state 11B NMR study of a series of 10 boronic acids and boronic esters with aromatic substituents are reported. Boron-11 electric field gradient (EFG) and chemical shift (CS) tensors obtained from analyses of spectra acquired in magnetic fields of 9.4 and 21.1 T are demonstrated to be useful for gaining insight into the molecular and electronic structure about the boron nucleus. Data collected at 21.1 T clearly show the effects of chemical shift anisotropy (CSA), with tensor spans (Ω) on the order of 10−40 ppm. Signal enhancements of up to 2.95 were achieved with a DFS-modified QCPMG pulse sequence. To understand the relationship between the measured tensors and the local structure better, calculations of the 11B EFG and magnetic shielding tensors for these compounds were conducted. The best agreement was found between experimental results and those obtained from GGA revPBE DFT calculations. A positive correlation was found between Ω and the dihedral angle (ϕCCBO), which describes the orientation of the boronic acid/ester functional group relative to an aromatic system bound to boron. The small boron CSA is discussed in terms of paramagnetic shielding contributions as well as diamagnetic shielding contributions. Although there is a region of overlap, both Ω and the 11B quadrupolar coupling constants tend to be larger for boronic acids than for the esters. We conclude that the span is generally the most characteristic boron NMR parameter of the molecular and electronic environment for boronic acids and esters, and show that the values result from a delicate interplay of several competing factors, including hydrogen bonding, the value of ϕCCBO, and the electron-donating or withdrawing substituents bound to the aromatic ring
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a solid state 11b nmr and computational study of boron electric field gradient and chemical shift tensors in boronic acids and boronic esters
Journal of Physical Chemistry A, 2010Co-Authors: Joseph W E Weiss, David L. BryceAbstract:The results of a solid-state (11)B NMR study of a series of 10 boronic acids and boronic esters with aromatic substituents are reported. Boron-11 electric field gradient (EFG) and chemical shift (CS) tensors obtained from analyses of spectra acquired in magnetic fields of 9.4 and 21.1 T are demonstrated to be useful for gaining insight into the molecular and electronic structure about the boron nucleus. Data collected at 21.1 T clearly show the effects of chemical shift anisotropy (CSA), with tensor spans (Omega) on the order of 10-40 ppm. Signal enhancements of up to 2.95 were achieved with a DFS-modified QCPMG pulse sequence. To understand the relationship between the measured tensors and the local structure better, calculations of the (11)B EFG and magnetic shielding tensors for these compounds were conducted. The best agreement was found between experimental results and those obtained from GGA revPBE DFT calculations. A positive correlation was found between Omega and the dihedral angle (phi(CCBO)), which describes the orientation of the boronic acid/ester functional group relative to an aromatic system bound to boron. The small boron CSA is discussed in terms of paramagnetic shielding contributions as well as diamagnetic shielding contributions. Although there is a region of overlap, both Omega and the (11)B quadrupolar coupling constants tend to be larger for boronic acids than for the esters. We conclude that the span is generally the most characteristic boron NMR parameter of the molecular and electronic environment for boronic acids and esters, and show that the values result from a delicate interplay of several competing factors, including hydrogen bonding, the value of phi(CCBO), and the electron-donating or withdrawing substituents bound to the aromatic ring.
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A Solid-State Multinuclear Magnetic Resonance Investigation of Hexamethylborazine
2002Co-Authors: Michelle A. M. Forgeron, David L. Bryce, Roderick E WasylishenAbstract:Analyses of 11B, 13C, and 2H NMR spectra of solid hexamethylborazine, I, provide conclusive evidence for rapid in-plane jumps of the borazine ring at room temperature. Boron-11 NMR spectra of magic-angle spinning (MAS) samples, acquired at low (4.7 T), moderate (9.4 T), and high (18.8 T) external applied magnetic field strengths, have been simulated to yield the 11B nuclear quadrupolar coupling constant (CQ), asymmetry parameter, and isotropic chemical shift; their values at 298 K are 2.98 ( 0.03 MHz, 0.01 ( 0.01, and 36.0 ( 0.4 ppm, respectively. Simulations of 13C CP/MAS NMR spectra provide the carbon-boron isotropic indirect spin-spin coupling constant, Jiso, the sign of CQ(11B), the relative orientations of the boron electric field gradient (EFG) and the 13C-11B dipolar coupling tensors, and the motionally averaged 13C-11B dipolar coupling constant. Variable-temperature 2H NMR spectra of a partially deuterated sample of I indicate that the in-plane jumps of the borazine ring are slow with respect to CQ(2H)-1 (i.e., ôjump g 10-4 s) at temperatures less than 130 K. Over the temperature range 180 to 128 K, 2H NMR line shape analysis yields an activation energy of 30.1 ( 1.5 kJ mol-1 for the in-plane jumps of the borazine ring. Although a precise experimental determination of boron chemical shift anisotropy was impeded by intramolecular and intermolecular boron-boron dipolar interactions and heteronuclear nitrogen-boron dipolar interactions, simulations of high-field 11B NMR spectra of a stationary sample of I suggest a value of 55 ( 15 ppm for the motionally averaged span of the chemical shift tensor. Lastly, high-level ab initio and density functional theory calculations provide values of the boron EFG tensor and the boron and nitrogen magnetic shielding tensors for a rigid molecule of I
Arnab Sarka - One of the best experts on this subject based on the ideXlab platform.
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advancing the analytical capabilities of laser ablation molecular isotopic spectrometry for boron isotopic analysis
Spectrochimica Acta Part B: Atomic Spectroscopy, 2014Co-Authors: Xianglei Mao, Arnab Sarka, Richard E RussoAbstract:Abstract Laser ablation molecular isotopic spectrometry (LAMIS) recently has been investigated for analysis of the boron isotopic composition in ambient air at atmospheric pressure. The initial precision of 100–400‰ (2σ) for the 10 B/ 11 B isotopic ratio was less than results obtained from other analytical methods like TIMS or ICP–MS. This paper describes how accuracy and precision for boron isotopic ratio using LAMIS can be improved to the few per mil level. Several optimization procedures, viz., spectral region of analysis, effect of flicker noise from matrix, spectral normalization and pre-treatment procedures, were studied. This paper reports a precision of 9‰ (2σ) for the 10 B/ 11 B ratio using alternative spectral normalization and pre-treatment procedures.
Shaoyong Jiang - One of the best experts on this subject based on the ideXlab platform.
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boron isotope geochemistry of salt sediments from the dongtai salt lake in qaidam basin boron budget and sources
Chemical Geology, 2014Co-Authors: Haizhen Wei, Shaoyong Jiang, Hongbing Tan, Wenjie Zhang, Tangli YangAbstract:Abstract Dongtai salt lake in Qaidam Basin contains abundant boron and lithium resources, and has the highest reserve of lithium found in the world, but the origin of these resources is highly controversial. In this study, we carried out a detailed study on chemical compositions and boron isotope characteristics of salt sediments collected from a drill core in the Dongtai salt lake. The evaporite, carbonate and silicate phases of the sediments show δ 11 B values of − 6.4‰ to + 2.2‰, − 17.3‰ to + 0.5‰ and − 14.6‰ to − 2.8‰, respectively, which suggest a non-marine origin for the salt lake. The variation of δ 11 B vs. K% identified the evolution process of the salt lake. The geochemical/hydrochemical signatures and the reserve estimation of boron resources approved the dominant sources of saline resources containing abundant B, K and Li from the inflowing Nalenggele River. The boron isotopic fractionation factors between evaporite and brine (i.e. α evaporite–brine ) vary from 0.9869 to 0.9955, and the linear variation of α evaporite–brine vs. Li/Mg molar ratios reflects the boron isotopic fractionation during crystallization of the salts. The positive correlation between δ 11 B and [B] in the carbonate phase reflects the pH control on the incorporation of boron into the carbonates, and the equilibrium isotope fractionation follows the Rayleigh isotope fractionation rule in a closed system. The variation of δ 11 B values in the silicate phase behaved as an oscillating pattern, and the more negative shift of δ 11 B values corresponds to the mudstone strata deposited under warm–humid climate conditions, indicating the influence of intensive weathering.
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an improved procedure for separation purification of boron from complex matrices and high precision measurement of boron isotopes by positive thermal ionization and multicollector inductively coupled plasma mass spectrometry
Talanta, 2014Co-Authors: Haizhen Wei, Gary N Hemming, Shaoyong Jiang, Tangli Yang, Jinghong Yang, Tao Yang, Xiong YanAbstract:Abstract In order to eliminate boron loss and potential isotopic fractionation during chemical pretreatment of natural samples with complex matrices, a three-column ion-exchange separation/purification procedure has been modified, which ensures more than 98% recovery of boron from each step for a wide range of sample matrices, and is applicable for boron isotope analysis by both TIMS and MC-ICP-MS. The PTIMS-Cs 2 BO 2 + -static double collection method was developed, ensuring simultaneous collection of 133 Cs 2 11 B 16 O 2 + ( m/z 309) and 133 Cs 2 10 B 16 O 2 + ( m/z 308) ions in adjacent H3–H4 Faraday cups with typical zoom optics parameters (Focus Quad: 15 V, Dispersion Quad: −85 V). The external reproducibilities of the measured 11 B/ 10 B ratios of the NIST 951 boron standard solutions of 1000 ng, 100 ng and 10 ng of boron by PTIMS method are ±0.06‰, ±0.16‰ and ±0.25‰, respectively, which indicates excellent precision can be achieved for boron isotope measurement at nanogram level boron in natural samples. An on-peak zero blank correction procedure was employed to correct the residual boron signals effect in MC-ICP-MS, which gives consistent δ 11 B values with a mean of 39.66±0.35‰ for seawater in the whole range of boron content from 5 ppb to 200 ppb, ensuring accurate boron isotope analysis in few ppb boron. With the improved protocol, consistent results between TIMS and MC-ICP-MS data were obtained in typical geological materials within a wide span of δ 11 B values ranging from −25‰ to +40‰.