Realtime stable isotope monitoring of natural waters by parallel-flow laser spectroscopy

A parallel-flow H(2)O(liquid)-H(2)O(vapor) equilibration and laser spectroscopy method provides a new way to monitor the hydrogen and oxygen stable isotopic composition of water from rivers or lakes or in hydrologic tracer tests in real time. Two custom-built equilibrator devices and one commercial membrane device were tested to determine if they could be used to convert natural water samples (lakes, rivers, groundwater) to a H(2)O gas phase for continuous online δ(18)O and δD isotopic analysis by laser spectroscopy. Both the commercial minimodule device and the marble-filled equilibrator produced water vapor in isotopic equilibrium with the flowing liquid water, suggesting that unattended field measurement using these devices is possible. Oxygen isotope disequilibrium was indicated using the minimodule device at low temperatures.     

Use of laser spectroscopy to measure the 13C/12C and 18O/16O compositions of carbonate minerals

The stable carbon and oxygen isotope compositions of carbonate minerals are utilized throughout the earth and environmental sciences for various purposes. Here, we demonstrate the first application of a prototype instrument, based on off-axis integrated cavity output laser spectroscopy, to measure the carbon and oxygen isotope composition of CO(2) gas evolved from the acidification of carbonate minerals. The carbon and oxygen isotope ratios were recorded from absorption spectra of (12)C(16)O(16)O, (13)C(16)O(16)O, and (12)C(16)O(18)O in the near-infrared wavelength region. The instrument was calibrated using CaCO(3) minerals with known δ(13)C(VPDB) and δ(18)O(VSMOW) values, which had been previously calibrated by isotope ratio mass spectrometry relative to the international isotopic standards NBS 18 and NBS 19. Individual analyses are demonstrated to have internal precision (1 SE) of better than 0.15‰ for δ(13)C and 0.6‰ for δ(18)O. Analysis of four carbonate standards of known isotopic composition over 2 months, determined using the original instrumental calibration, indicates that analyses are accurate to better than 0.5‰ for both δ(13)C and δ(18)O without application of standard-sample-standard corrections.     

An On-Line Technique for the Determination of the δ(18)O and δ(17)O of Gaseous and Dissolved Oxygen

Few studies have used the stable isotopic composition of O(2) as a tracer of gas transport or biogeochemical processes in environmental research. Here we demonstrate field sampling techniques for gaseous and dissolved O(2) and describe an analytical method for measuring δ(18)O and δ(17)O values of O(2) in air, soil gas, and water samples using continuous-flow isotope-ratio mass spectrometry (CF-IRMS). A Micromass CF-IRMS was altered to accommodate a sample gas injection port prior to a CO(2) and H(2)O trap and GC column. The GC column was a 1-m, 5-? molecular sieve column held at 35 °C. The resolved sample O(2) was introduced to the IRMS via an open split. δ(18)O and δ(17)O values were determined by measurement of O(2) isotopes at m/z 34/32 and 33/32 and comparison to a reference pulse of O(2). Repeated injections of atmospheric oxygen yielded a repeatability (±SD) of ±0.17‰ for δ(18)O and ±0.5‰ for δ(17)O. IRMS source linearity was excellent for O(2) over a sample size range of 60-400 μL. The smallest sample for routine δ(18)O and δ(17)O determinations was ～80 μL of O(2), with a sample analysis time of 180 s. Preliminary results from a riverine and soil gas study illustrate natural oxygen isotope fractionation processes.     

Determination of δ(18)O and δ(15)N in Nitrate

The analyses of both O and N isotopic compositions of nitrate have many potential applications in studies of nitrate sources and reactions in hydrology, oceanography, and atmospheric chemistry, but simple and precise methods for these analyses have yet to be developed. Testing of a new method involving reaction of potassium nitrate with catalyzed graphite (C + Pd + Au) at 520 °C resulted in quantitative recovery of N and O from nitrate as free CO(2), K(2)CO(3), and N(2). The δ(18)O values of nitrate reference materials were obtained by analyzing both the CO(2) and K(2)CO(3) from catalyzed graphite combustion. Provisional values of δ(18)O(VSMOW) for the internationally distributed KNO(3) reference materials IAEA-N3 and USGS-32 were both equal to +22.7 ± 0.5‰. Because the fraction of free CO(2) and the isotopic fractionation factor between CO(2) and K(2)CO(3) were constant in the combustion products, the δ(18)O value of KNO(3) could be calculated from measurements of the δ(18)O of free CO(2). Thus, δ(18)O(KNO)((3)) = aδ(18)O(free)(?)(CO)((2)) - b, where a and b were equal to 0.9967 and 3.3, respectively, for the specific conditions of the experiments. The catalyzed graphite combustion method can be used to determine δ(18)O of KNO(3) from measurements of δ(18)O of free CO(2) with reproducibility on the order of ±0.2‰ or better if local reference materials are prepared and analyzed with the samples. Reproducibility of δ(15)N was ±0.1‰ after trace amounts of CO were removed.     

Determination of boron in tissues and cells using direct-current plasma atomic emission spectroscopy

We have developed a safe, simple, and efficient method for boron determination by means of direct-current plasma atomic emission spectroscopy. Tissues were solubilized by using concentrated sulfuric acid and 70% hydrogen peroxide to digest the samples without the need of high temperatures and pressures. Boron cluster compounds could be measured with sensitivity, precision, and accuracy similar to those of boric acid standards. Results obtained with [(C2H5)3NH]2B12H12, Cs2B12H11SH.H2O, and C15H32B10O6 show that this analytical method is applicable to a variety of compounds with different chemical structures. A sensitivity of 0.1 ppm has been obtained with known standards alone and in a variety of tissue matrices including tumor, blood, liver, skin, and cell suspensions. The measurement of total boron by direct-current plasma atomic emission spectroscopy (DCP-AES) has been achieved with as little as 50 mg of tissue or as few as 5 x 10(7) cells. The procedure is applicable to the analysis of boron in the ppm range with a high degree of precision and accuracy.     

Estimation of the isotopic effect on the melting parameters of boron

It is shown that the isotopic composition has a noticeable effect on the melting parameters of boron. The differences in melting temperature and enthalpy of the monoisotopes ¹⁰B and ¹¹B are estimated at ∼16 K and ∼0.0021 eV/at, respectively. Published in Russian in Neorganicheskie Materialy, 2007, Vol. 43, No. 6, pp. 676–679.     

Boron foils for RDDS experiment

Application of the deposition method based on the vibrational motion of micro particles in an electrostatic field [I. Sugai, Nucl. Instr. and Meth. A 397 (1997) 81] is described for the production of isotopic ¹¹B foils. The method proved suitable for target production of this typically brittle material when a very flat target surface was required. The goal to produce ¹¹B targets of 160–350 μg/cm² was achieved by depositing the boron on a thin foil substrate, such as Nb and Sn. The coated foil was stretched flat before it was mounted on a frame.     

Correcting for methane interferences on δ2H and δ18O measurements in pore water using H2Oliquid-H2Ovapor equilibration laser spectroscopy

Cavity ring-down spectroscopy (CRDS) is a new and evolving technology that shows great promise for isotopic δ(18)O and δ(2)H analyses of pore water from equilibrated headspace H(2)O vapor from environmental and geologic cores. We show that naturally occurring levels of CH(4) can seriously interfere with CRDS spectra, leading to erroneous δ(18)O and δ(2)H results for water. We created a new CRDS correction algorithm to account for CH(4) concentrations typically observed in subsurface and anaerobic environments, such as ground waters or lake bottom sediments. We subsequently applied the correction method to a series of geologic cores that contain CH(4). The correction overcomes the spectral interference and provides accurate pore water δ(18)O and δ(2)H values with acceptable precision levels as well as accurate concentrations of CH(4).     

Isotopic characterization of targets for nuclear measurements at CBNM

Nuclear measurements for which “nuclear” targets are prepared are almost always isotope-specific i.e. they are normally related to a particular nuclide present in the target. The amount of this nuclide must be accurately assessed. There are essentially two ways to determine the number of atoms of this particular nuclide.(1) By determination of the amount of element, to which the nuclide belongs, on the target via classical means: weighing, subtraction of impurities, calculation of element amount using known stoichiometry of the chemical compound in which the element is incorporated and, finally, measurement of the isotopic composition in order to determine the fraction of the nuclide concerned in the element. An alternative way may be to perform an elemental assay on the target followed by determination of the isotopic composition.(2) Another approach is isotope dilution mass spectrometry where a change in the isotopic composition of the “target” is induced by adding a known number of atoms (called “spike”) of the element with a quite different composition. Measurement of the resulting change in isotopic composition yields directly the number of atoms of the nuclide under investigation. The method is highly selective, accurate and isotope-specific.     

Preparation of self-supporting boron targets

The procedure for the fabrication of self-supporting isotopically enriched ¹¹B targets for the application to nuclear scattering measurements using an electron-beam-excited plasma (EBEP) method was described. A boron target layer of thickness 100±10 μg/cm² was obtained. The thickness and uniformity of the prepared ¹¹B film were determined by measuring the energy loss of alpha particles across the target area. The purity of the target was examined, and it was found that the investigated boron film contained about 10% impurities.     

Simultaneous determination of the (2)h/(1)h, (17)o/(16)o, and (18)o/(16)o isotope abundance ratios in water by means of laser spectrometry

We demonstrate the first successful application of infrared laser spectrometry to the accurate, simultaneous determination of the relative (2)H/(1)H, (17)O/(16)O, and (18)O/(16)O isotope abundance ratios in water. The method uses a narrow line width color center laser to record the direct absorption spectrum of low-pressure gas-phase water samples (presently 10 μL of liquid) in the 3-μm spectral region. It thus avoids the laborious chemical preparations of the sample that are required in the case of the conventional isotope ratio mass spectrometer measurement. The precision of the spectroscopic technique is shown to be 0.7‰ for δ(2)H and 0.5‰ for δ(17)O and δ(18)O (δ represents the relative deviation of a sample's isotope abundance ratio with respect to that of a calibration material), while the calibrated accuracy amounts to about 3 and 1‰, respectively, for water with an isotopic composition in the range of the Standard Light Antarctic Precipitation and Vienna Standard Mean Ocean Water international standards.     

Electron-beam deposited boron coatings for the extreme ultraviolet

Boron films deposited by evaporation with an electron-beam were found to have a relatively high reflectance in the extreme ultraviolet with values similar to those of ion-beam-sputtered (IBS) SiC and IBS B(4)C. The largest reflectance was measured for an 11 nm thick boron film. Some reflectance degradation was observed for boron films stored in a desiccator. Reflectance degradation varied from sample to sample and was found to be either similar to that of IBS SiC and IBS B(4)C or larger.     

Thermal Heating Induced Fractionation Effect on δ<Superscript>15</Superscript>N Measurements (Using Continuous Flow Isotope Ratio Mass-Spectrometry) for Samples Containing Lower N Contents

Simultaneous measurements of stable isotopes of Nitrogen (N), Carbon (C) and Sulfur (S) in a single aliquot of sample using stable isotope mass spectrometry coupled with elemental analyzer (EA) in a continuous flow mode has provided added advantages for stable isotopic data community scientifically as well as economically. For NCS isotopic measurements, certain configurational changes were adapted in the EA setup such as (1) introduction of ‘purge and trap columns’ for adsorbing and desorbing analyte CO₂ and SO₂, and (2) introduction of in-line ring heater to cover for the entire passage between combustion and reduction reactor to prevent any condensation of analyte gases. These modifications were made to achieve necessary accuracy and precision NCS isotopic measurements. However, the presence of in-line ring heater appears to have an influence on δ¹⁵N measurements especially for samples containing lower N amounts (≤2 μmoles). We compared δ¹⁵N measurements in both NCS and NC modes by reconfiguring same EA (Vario Pyrocube) connected with Isoprime mass spectrometer with wide range variability in N content. We observed a decreasing pattern in δ¹⁵N values with increasing N contents (till the true δ¹⁵N value is approached), which is an opposite trend compared to that typically observed with the NC mode of EA setup. We surmise thermal heating of the passage from the combustion and reduction reactors is most likely responsible for the observed pattern. Measured δ¹⁵N values for samples containing lower N (≤2 μmoles), however, could be corrected using appropriate correction procedure.     

Boron microquantification in oral muscosa and skin following administration of a neutron capture therapy agent

Clinical trials of boron neutron capture therapy (BNCT) for intracranial tumours using boronophenylalanine-fructose undertaken at Harvard-MIT and Brookhaven National Laboratory have observed acute normal tissue reactions in the skin and oral mucosa. Because the range of the 10B(n, alpha)7Li reaction products is very short, 10-14 microns combined, knowledge of the 10B microdistribution in tissue is critical for understanding the microdosimetry and radiobiology of BNCT. This paper reports measurements of the microdistribution of 10B in an animal model, rat skin and tongue, using high resolution quantitative autoradiography (HRQAR), a neutron-induced etched track autoradiographic technique. The steep spatial gradient and high absolute value relative to blood of the 10B concentration observed in some strata of the rat tongue epithelium and skin are important for properly evaluating the radiobiology and the biological effectiveness factors for normal tissue reactions such as oral mucositis, which are generally assessed using the blood boron concentration rather than the tissue boron concentration.     

Carbon isotopes profiles of human whole blood, plasma, red blood cells, urine and feces for biological/biomedical 14C-accelerator mass spectrometry applications

Radiocarbon ((14)C) is an ideal tracer for in vivo human ADME (absorption, distribution, metabolism, elimination) and PBPK (physiological-based pharmacokinetic) studies. Living plants peferentially incorporate atmospheric (14)CO(2) versus (13)CO(2) versus (12)CO(2), which result in unique signature. Furthermore, plants and the food chains they support also have unique carbon isotope signatures. Humans, at the top of the food chain, consequently acquire isotopic concentrations in the tissues and body fluids depending on their dietary habits. In preparation of ADME and PBPK studies, 12 healthy subjects were recruited. The human baseline (specific to each individual and their diet) total carbon (TC) and carbon isotope (13)C (δ(13)C) and (14)C (F(m)) were quantified in whole blood (WB), plasma, washed red blood cell (RBC), urine, and feces. TC (mg of C/100 μL) in WB, plasma, RBC, urine, and feces were 11.0, 4.37, 7.57, 0.53, and 1.90, respectively. TC in WB, RBC, and feces was higher in men over women, P < 0.05. Mean δ(13)C were ranked low to high as follows: feces < WB = plasma = RBC = urine, P < 0.0001. δ(13)C was not affected by gender. Our analytic method shifted δ(13)C by only ±1.0 ‰ ensuring our F(m) measurements were accurate and precise. Mean F(m) were ranked low to high as follows: plasma = urine < WB = RBC = feces, P < 0.05. F(m) in feces was higher for men over women, P < 0.05. Only in WB, (14)C levels (F(m)) and TC were correlated with one another (r = 0.746, P < 0.01). Considering the lag time to incorporate atmospheric (14)C into plant foods (vegetarian) and or then into animal foods (nonvegetarian), the measured F(m) of WB in our population (recruited April 2009) was 1.0468 ± 0.0022 (mean ± SD), and the F(m) of WB matched the (extrapolated) atmospheric F(m) of 1.0477 in 2008. This study is important in presenting a procedure to determine a baseline for a study group for human ADME and PBPK studies using (14)C as a tracer.     

Boron removal and recovery from concentrated wastewater using a microwave hydrothermal method

Boron compounds are widely-used raw materials in industries. However, elevated boron concentrations in aqueous systems may be harmful to human and plants. In this study, calcium hydroxide (Ca(OH)(2)) alone and Ca(OH)(2) with phosphoric acid (H(3)PO(4)) addition (P-addition) were used to remove and recover boron from wastewater using hydrothermal methods. A microwave (MW) hydrothermal method was used and compared with the conventional heating (CH) method in batch experiments. Physicochemical properties of the precipitates obtained from both methods were analysed by XRD, SEM with EDX and BET. For the case of Ca(OH)(2) alone and the MW method, experimental results showed that boron recovery efficiency reached 90% within 10 min, and crystals of Ca(2)B(2)O(5)·H(2)O were found in the precipitates as indicated by the XRD analysis. For the case of P-addition and the MW method, boron recovery efficiency reached 99% within 10 min, and calcium phosphate species (CaHPO(4)·H(2)O, CaHPO(4) and Ca(10)(PO(4))(6)(OH)(2)) were formed. The experimental results of this study indicate that the required reaction time of the MW method was much less than that of the CH method, and the MW method is an effective and efficient method for boron removal and recovery from concentrated wastewater.     

Stable isotope assisted assignment of elemental compositions for metabolomics

Assignment of individual compound identities within mixtures of thousands of metabolites in biological extracts is a major challenge for metabolomic technology. Mass spectrometry offers high sensitivity over a large dynamic range of abundances and molecular weights but is limited in its capacity to discriminate isobaric compounds. In this article, we have extended earlier studies using isotopic labeling for elemental composition elucidation (Rodgers, R. P.; Blumer, E. N.; Hendrickson, C. L.; Marshall, A. G. J. Am. Soc. Mass Spectrom. 2000, 11, 835-40) to limit the formulas consistent with any exact mass measurement by comparing observations of metabolites extracted from Arabidopsis thaliana plants grown with (I) (12)C and (14)N (natural abundance), (II) (12)C and (15)N, (III) (13)C and (14)N, or (IV) (13)C and (15)N. Unique elemental compositions were determined over a dramatically enhanced mass range by analyzing exact mass measurement data from the four extracts using two methods. In the first, metabolite masses were matched with a library of 11,000 compounds known to be present in living cells by using values calculated for each of the four isotopic conditions. In the second method, metabolite masses were searched against masses calculated for a constrained subset of possible atomic combinations in all four isotopic regimes. In both methods, the lists of elemental compositions from each labeling regime were compared to find common formulas with similar retention properties by HPLC in at least three of the four regimes. These results demonstrate that metabolic labeling can be used to provide additional constraints for higher confidence formula assignments over an extended mass range.     

Carbon isotope composition of dissolved humic and fulvic acids in the Tokachi River system

This study reports carbon isotopic ratios (Δ(14)C and δ(13)C) of dissolved humic and fulvic acids in the Tokachi River system, northern Japan. These acids have a refractory feature and they represent the largest fraction of dissolved organic matter in aquatic environments. The acids were isolated using the XAD extraction method from river water samples collected at three sites (on the upper and lower Tokachi River, and from one of its tributaries) in June 2004 and 2005. δ(13)C values were -27.8 to -26.9 ‰ for humic and fulvic acids. On the other hand, the Δ(14)C values ranged from -247 to +26 ‰ and the average values were -170 ± 79 ‰ for humic acid and -44 ± 73 ‰ for fulvic acid. The difference was attributed to the residence time of fulvic acid in the watershed being shorter than that of humic acid. The large variation suggested that humic substances have a different pathway in each watershed environment.     

New Cluster Secondary Ions for Quantitative Analysis of the Concentration of Boron Atoms in Diamond by Time-of-Flight Secondary-Ion Mass Spectrometry

A new approach to quantitative analysis of the concentration of boron atoms in diamond using secondary- ion mass spectrometers with time-of-flight mass analyzers is proposed. Along with the known boron-containing lines (B, BC, BC₂), many lines related to cluster secondary ions BC _N have been found in the mass spectrum; their intensity increases by one or two orders of magnitude when Bi₃ probe ions are used. Lines BC₄, BC₆, BC₂, and BC₈ have the highest intensity (in the descending order); when they are summed, the sensitivity increases by an order of magnitude in comparison with the known mode of detecting BC₂. The parameters of the boron δ-layer in single-crystal diamond films grown under optimal conditions have been measured to be unprecedented: the δ-layer width is about 2 nm, and the concentration is 6.4 × 10²⁰ cm^–3 (the boron concentrations for doped and undoped diamonds differ by four orders of magnitude).     

A gas chromatographic separation for the h and C stable isotope ratio determination of coal compounds

A new, completely automated gas chromatography technique has been developed to separate the different gaseous compounds produced during underground coal gasification for their (13)C/(12)C and D/H isotope ratio measurements. The technique was designed for separation and collection of H(2), CO, CO(2), H(2)O, H(2)S, CH(4), and heavier hydrocarbons. These gaseous compounds are perfectly separated by the gas-phase chromatograph and quantitatively sent to seven combustion and collection lines. H(2), CO, CH(4), and heavier hydrocarbons are quantitatively oxidized to CO(2) and/or H(2)O. The isotopic analyses are performed by the sealed-tube method. The zinc method is used for reduction of both water and H(2)S to hydrogen for D/H analysis. Including all preparation steps, the reproducibility of isotope abundance values, for a quantity higher than or equal to 0.1 mL of individual components in a mixture (5 mL of gases being initially injected in the gas chromatograph), is ±0.1‰ for δ(13)C(PDB) and ±6‰ for δD(SMOW).