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The purpose of the Reston Stable Isotope Laboratory (RSIL) lab code 1949 is to determine the δ(34S/32S), abbreviated as δ34S, of dissolved sulfate having a concentration less than 20 milligrams per liter. Dissolved sulfate is collected on an anion-exchange resin in the field, eluted in the laboratory with 3 M KCl, and precipitated with BaCl2 at pH 3 to 4 as BaSO4. The precipitated BaSO4 is filtered and dried before introduction into an elemental analyzer (EA) Carlo Erba NC 2500. The EA is used to convert sulfur in a BaSO4 solid sample into SO2 gas, and the EA is connected to a continuous flow isotope-ratio mass spectrometer (CF-IRMS), which determines differences in the isotope-amount ratios of stable sulfur isotopes...
Categories: Publication;
Types: Citation
Precipitation samples for measurement of stable-isotope ratios of hydrogen (delta2H) and oxygen (delta18O) were collected at the Norman Landfill Research Site in Norman, Oklahoma, from May 1996 to October 2008. Rainfall amounts also were measured at the site (U.S. Geological Survey gaging station 07229053) during the collection period. The delta2H of precipitation samples ranged from -121.9 to +8.3 per mil, and the delta18O of precipitation ranged from -16.96 to +0.50 per mil. The volume-weighted average values for delta2H and delta18O of precipitation over the 12-year measurement period were -31.13 per mil for delta2H and -5.57 per mil for delta18O. Average summer-season delta2H and delta18O values of precipitation...
Categories: Publication;
Types: Citation
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...
Categories: Publication;
Types: Citation
The purpose of the Reston Stable Isotope Laboratory (RSIL) lab code 2900 is to determine the δ15N and δ18O of nitrate (NO3-) in water. The δ15N and δ18O of the dissolved NO3- are analyzed by converting the NO3- to nitrous oxide (N2O), which serves as the analyte for mass spectrometry. A culture of denitrifying bacteria is used in the enzymatic conversion of the NO3- to N2O, which follows the pathway shown in equation 1: NO3- → NO2- → NO → 1/2 N2O (1) Because the bacteria Pseudomonas aureofaciens lack N2O reductive activity, the reaction stops at N2O, unlike the typical denitrification reaction that goes to N2. After several hours, the conversion is complete, and the N2O is extracted from the vial, separated from...
Categories: Publication;
Types: Citation
The purpose of the Reston Stable Isotope Laboratory (RSIL) lab code 1832 is to determine the δ(15N/14N), abbreviated as δ15N, and the δ(13C/12C), abbreviated as δ13C, of total nitrogen and carbon in a solid sample. A Carlo Erba NC 2500 elemental analyzer (EA) is used to convert total nitrogen and carbon in a solid sample into N2 and CO2 gas. The EA is connected to a continuous flow isotope-ratio mass spectrometer (CF-IRMS), which determines the relative difference in stable nitrogen isotope-amount ratio (15N/14N) of the product N2 gas and the relative difference in stable carbon isotope-amount ratio (13C/12C) of the product CO2 gas. The combustion is quantitative; no isotopic fractionation is involved. Samples are...
Categories: Publication;
Types: Citation
The purpose of the Reston Stable Isotope Laboratory (RSIL) lab code 2893 is to determine the δ(15N/14N), abbreviated as δ15N , of total nitrogen in solid samples. A Carlo Erba NC 2500 elemental analyzer (EA) is used to convert total nitrogen in a solid sample into N2 gas. The EA is connected to a continuous flow isotope-ratio mass spectrometer (CF-IRMS), which determines relative difference in the isotope-amount ratios of stable nitrogen isotopes (15N/14N)of the product N2 gas. The combustion is quantitative; no isotopic fractionation is involved. Samples are placed in a tin capsule and loaded into the Costech Zero Blank Autosampler of the EA. Under computer control, samples are dropped into a heated reaction tube...
Categories: Publication;
Types: Citation
The purpose of the Reston Stable Isotope Laboratory (RSIL) lab code 2897 is to determine the δ15N and δ18O of nitrate (NO3-) in solids. The NO3- fraction of the nitrogen species is dissolved by water (called leaching) and can be analyzed by the bacterial method covered in RSIL lab code 2900. After leaching, the δ15N and δ18O of the dissolved NO3- is analyzed by conversion of the NO3- to nitrous oxide (N2O), which serves as the analyte for mass spectrometry. A culture of denitrifying bacteria is used in the enzymatic conversion of NO3- to N2O, which follows the pathway shown in equation 1: NO3- → NO2- → NO → 1/2 N2O (1) Because the bacteria Pseudomonas aureofaciens lack N2O reductive activity, the reaction stops...
Categories: Publication;
Types: Citation
The purpose of the Reston Stable Isotope Laboratory (RSIL) lab code 2899 is to determine the δ15N of nitrate (NO3-) in water. The δ15N of the dissolved NO3- is analyzed by conversion of the NO3- to nitrous oxide (N2O), which serves as the analyte for mass spectrometry. A culture of denitrifying bacteria is used in the enzymatic conversion of the NO3- to N2O, which follows the pathway shown in equation 1: NO3- → NO2- → NO → 1/2 N2O (1) Because the bacteria Pseudomonas aureofaciens lack N2O reductive activity, the reaction stops at N2O, unlike the typical denitrification reaction that goes to N2. After several hours, the conversion is complete, and the N2O is extracted from the vial, separated from volatile organic...
Categories: Publication;
Types: Citation
The purpose of the Reston Stable Isotope Laboratory (RSIL) lab code 2894 is to determine the δ15N of nitrate (NO3-) in solids. The nitrate fraction of the nitrogen species is dissolved by water (called leaching) and can be analyzed by the bacterial method covered in RSIL lab code 2899. After leaching, the δ15N of the dissolved NO3- is analyzed by conversion of the NO3- to nitrous oxide (N2O), which serves as the analyte for mass spectrometry. A culture of denitrifying bacteria is used in the enzymatic conversion of NO3- to N2O, which follows the pathway shown in equation 1: NO3- → NO2- → NO → 1/2 N2O (1) Because the bacteria Pseudomonas aureofaciens lack N2O reductive activity, the reaction stops at N2O, unlike...
Categories: Publication;
Types: Citation
The purpose of Reston Stable Isotope Laboratory Lab (RSIL) Code 1800 is to determine the δ(34S/32S), abbreviated as δ34S, of total sulfur in a solid sample. A Carlo Erba NC 2500 elemental analyzer (EA) is used to convert total sulfur in a solid sample into SO2 gas. The EA is connected to a continuous flow isotope-ratio mass spectrometer (CF-IRMS), which determines the relative difference in stable sulfur isotope-amount ratio (34S/32S) of the product SO2 gas. The combustion is quantitative; no isotopic fractionation is involved. Samples are placed in tin capsules and loaded into a Costech Zero-Blank Autosampler on the EA. Under computer control, samples are dropped into a heated tube reaction tube that combines both...
Categories: Publication;
Types: Citation
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 VSMOW2b and SLAP reference waters. These materials were used to calibrate the other isotopic reference materials in this study, which yielded: Reference...
Categories: Publication;
Types: Citation
Accurate hydrogen isotopic measurements of keratin materials have been a challenge due to exchangeable hydrogen in the sample matrix and the paucity of appropriate isotopic reference materials for calibration. We found that the most reproducible δ2HVSMOW-SLAP and mole fraction of exchangeable hydrogen, x(H)ex, of keratin materials were measured with equilibration at ambient temperature using two desiccators and two different equilibration waters with two sets of the keratin materials for 6 days. Following equilibration, drying the keratin materials in a vacuum oven for 4 days at 60 °C was most critical. The δ2H analysis protocol also includes interspersing isotopic reference waters in silver tubes among samples...
Categories: Publication;
Types: Citation
Because there are no internationally distributed stable hydrogen and oxygen isotopic reference materials of human hair, the U.S. Geological Survey (USGS) has prepared two such materials, USGS42 and USGS43. These reference materials span values commonly encountered in human hair stable isotope analysis and are isotopically homogeneous at sample sizes larger than 0.2 mg. USGS42 and USGS43 human-hair isotopic reference materials are intended for calibration of δ2H and δ18O measurements of unknown human hair by quantifying (1) drift with time, (2) mass-dependent isotopic fractionation, and (3) isotope-ratio-scale contraction. While they are intended for measurements of the stable isotopes of hydrogen and oxygen, they...
An anomalous stable hydrogen isotopic fractionation of 4 ? in gaseous hydrogen has been correlated with the process of adding liquid nitrogen (LN2) to top off the dewar of a stainless-steel water trap on a gaseous hydrogen?water platinum equilibration system. Although the cause of this isotopic fractionation is unknown, its effect can be mitigated by (1) increasing the capacity of any dewars so that they do not need to be filled during a daily analytic run, (2) interspersing isotopic reference waters among unknowns, and (3) applying a linear drift correction and linear normalization to isotopic results with a program such as Laboratory Information Management System (LIMS) for Light Stable Isotopes. With adoption...
Categories: Publication;
Types: Citation
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...
Categories: Publication;
Types: Citation
Precipitation samples for measurement of stable-isotope ratios of hydrogen (delta2H) and oxygen (delta18O) were collected at the Norman Landfill Research Site in Norman, Oklahoma, from May 1996 to October 2008. Rainfall amounts also were measured at the site (U.S. Geological Survey gaging station 07229053) during the collection period. The delta2H of precipitation samples ranged from -121.9 to +8.3 per mil, and the delta18O of precipitation ranged from -16.96 to +0.50 per mil. The volume-weighted average values for delta2H and delta18O of precipitation over the 12-year measurement period were -31.13 per mil for delta2H and -5.57 per mil for delta18O. Average summer-season delta2H and delta18O values of precipitation...
Categories: Publication;
Types: Citation
The purpose of the Reston Stable Isotope Laboratory (RSIL) lab code 1951 is to determine the δ(34S/32S), abbreviated as δ34S, of dissolved sulfate. Dissolved sulfate is collected in the field and precipitated with BaCl2 at pH 3 to 4 as BaSO4 in the laboratory. However, the dissolved organic sulfur (DOS) is oxidized to SO2, and the carbonate is acidified to CO2. Both are degassed from the water sample before the sulfate is precipitated. The precipitated BaSO4 is filtered and dried before introduction into an elemental analyzer (EA) Carlo Erba NC 2500. The EA is used to convert sulfur in a BaSO4 solid sample into SO2 gas, and the EA is connected to a continuous flow isotope-ratio mass spectrometer (CF-IRMS), which...
Categories: Publication;
Types: Citation
It is well known that N2 in the ion source of a mass spectrometer interferes with the CO background during the δ18O measurement of carbon monoxide. A similar problem arises with the high-temperature conversion (HTC) analysis of nitrogenous O-bearing samples (e.g. nitrates and keratins) to CO for δ18O measurement, where the sample introduces a significant N2 peak before the CO peak, making determination of accurate oxygen isotope ratios difficult. Although using a gas chromatography (GC) column longer than that commonly provided by manufacturers (0.6 m) can improve the efficiency of separation of CO and N2 and using a valve to divert nitrogen and prevent it from entering the ion source of a mass spectrometer improved...
Categories: Publication;
Types: Citation
Analytical grade L-glutamic acid is chemically stable and has a C/N mole ratio of 5, which is close to that of many of natural biological materials, such as blood and animal tissue. Two L-glutamic acid reference materials with substantially different 13C and 15N abundances have been prepared for use as organic reference materials for C and N isotopic measurements. USGS40 is analytical grade L-glutamic acid and has a δ13C value of −26.24‰ relative to VPDB and a δ15N value of −4.52‰ relative to N2 in air. USGS41 was prepared by dissolving analytical grade L-glutamic acid with L-glutamic acid enriched in 13C and 15N. USGS41 has a δ13C value of +37.76‰ and a δ15N value of +47.57‰. The δ13C and δ15N values of both materials...
Categories: Publication;
Types: Citation
The δ2HVSMOW–SLAP value of total hydrogen of the international measurement standard NBS 22 oil was determined by a new method of sealing water in silver tubes for use in a thermal conversion elemental analysis (TC/EA) reduction unit. The isotopic fractionation of water due to evaporation is virtually non-existent in this silver-tube method. A new value for the δ2HVSMOW–SLAP of NBS 22 oil, calibrated with isotopic reference waters, was determined to be −116.9 ± 0.8‰ (1σ and n = 31). Published in 2010 by John Wiley & Sons, Ltd.
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Types: Citation
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