Geology topics

Janet E. Hannon

Publications and source records attributed to Janet E. Hannon.

8 recordsLinked to original sources

USGS2008

Effects of nitrate and water on the oxygen isotopic analysis of barium sulfate precipitated from water samples

BaSO 4 precipitated from mixed salt solutions by common techniques for SO isotopic analysis may contain quantities of H 2 O and NO that introduce errors in O isotope measurements. Experiments with synthetic solutions indicate that δ 18 O values of CO produced by decomposition of precipitated BaSO 4 in a carbon reactor may be either too low or too high, depending on the relative concentrations of SO and NO and the δ 18 O values of the H 2 O, NO , and SO . Typical δ 18 O errors are of the order of 0.5 to 1‰ in many sample types, and can be larger in samples containing atmospheric NO , which can cause similar errors in δ 17 O and Δ 17 O. These errors can be reduced by (1) ion chromatographic separation of SO from NO , (2) increasing the salinity of the solutions before precipitating BaSO 4 to minimize incorporation of H 2 O, (3) heating BaSO 4 under vacuum to remove H 2 O, (4) preparing isotopic reference materials as aqueous samples to mimic the conditions of the samples, and (5) adjusting measured δ 18 O values based on amounts and isotopic compositions of coexisting H 2 O and NO . These procedures are demonstrated for SO isotopic reference materials, synthetic solutions with isotopically known reagents, atmospheric deposition from Shenandoah National Park, Virginia, USA, and sulfate salt deposits from the Atacama Desert, Chile, and Mojave Desert, California, USA. These results have implications for the calibration and use of O isotope data in studies of SO sources and reaction mechanisms.

Rapid Communications in Mass Spectrometry↗

USGS2008

Determination of the delta(15N/14N)of Ammonium (NH4+) in Water: RSIL Lab Code 2898

The purpose of the technique described by Reston Stable Isotope Laboratory (RSIL) lab code 2898 is to determine the N isotopic composition, delta(15N/14N), abbreviated as d15N, of ammonium (NH4+) in water (freshwater and saline water). The procedure involves converting dissolved NH4+ into NH3 gas by raising the pH of the sample to above 9 with MgO and subsequently trapping the gas quantitatively as (NH4)2SO4 on a glass fiber (GF) filter. The GF filter is saturated with NaHSO4 and pressure sealed between two gas-permeable polypropylene filters. The GF filter 'sandwich' floats on the surface of the water sample in a closed bottle. NH3 diffuses from the water through the polypropylene filter and reacts with NaHSO4, forming (NH4)2SO4 on the GF filter. The GF filter containing (NH4)2SO4 is dried and then combusted with a Carlo Erba NC 2500 elemental analyzer (EA), which 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 the relative difference in ratios of the amounts of the stable isotopes of nitrogen (15N and 14N) of the product N2 gas and a reference N2 gas. The filters containing the samples are compressed in tin capsules and loaded into a Costech Zero-Blank Autosampler on the EA. Under computer control, samples then are dropped into a heated reaction tube that contains an oxidant, where combustion takes place in a He atmosphere containing an excess of O2 gas. To remove S-O gases produced from the NaHSO4, a plug of Ag-coated Cu wool is inserted at the bottom of the reaction tube. Combustion products are transported by a He carrier through a reduction furnace to remove excess O2, toconvert all nitrogen oxides to N2, and to remove any remaining S-O gases. The gases then pass through a drying tube to remove water. The gas-phase products, mainly N2 and a small amount of background CO2, are separated by a gas chromatograph (GC). The gas is then introduced into the IRMS through a Finnigan ConFlo II interface. The ConFlo II interface is used to introduce not only sample into the IRMS but also N2 reference gas and He for sample dilution. The flash combustion is quantitative, so no isotopic fractionation is involved. The IRMS is a Finnigan Delta V CF-IRMS with 10 cups and is capable of detecting ion beams with mass/charge (m/z) 28, 29, 30. The ion beams from N2 are as follows: m/z 28 = 14N14N, m/z 29 = 14N15N, and m/z 30 = 15N15N. The ion beam with m/z 30 also represents 14N16O, which may indicate contamination or incomplete reduction.

Techniques and Methods↗

USGS2007

Isotopic analysis of N and O in nitrite and nitrate by sequential selective bacterial reduction to N2O

Nitrite is an important intermediate species in the biogeochemical cycling of nitrogen, but its role in natural aquatic systems is poorly understood. Isotopic data can be used to study the sources and transformations of NO 2 - in the environment, but methods for independent isotopic analyses of NO 2 - in the presence of other N species are still new and evolving. This study demonstrates that isotopic analyses of N and O in NO 2 - can be done by treating whole freshwater or saltwater samples with the denitrifying bacterium Stenotrophomonas nitritireducens , which selectively reduces NO 2 - to N 2 O for isotope ratio mass spectrometry. When calibrated with solutions containing NO 2 - with known isotopic compositions determined independently, reproducible δ 15 N and δ 18 O values were obtained at both natural-abundance levels (±0.2−0.5‰ for δ 15 N and ±0.4−1.0‰ for δ 18 O) and moderately enriched 15 N tracer levels (±20−50‰ for δ 15 N near 5000‰) for 5−20 nmol of NO 2 - (1−20 μmol/L in 1−5 mL aliquots). This method is highly selective for NO 2 - and was used for mixed samples containing both NO 2 - and NO 3 - with little or no measurable cross-contamination. In addition, mixed samples that were analyzed with S. nitritireducens were treated subsequently with Pseudomonas aureofaciens to reduce the NO 3 - in the absence of NO 2 - , providing isotopic analyses of NO 2 - and NO 3 - separately in the same aliquot. Sequential bacterial reduction methods like this one should be useful for a variety of isotopic studies aimed at understanding nitrogen cycling in aquatic environments. A test of these methods in an agricultural watershed in Indiana provides isotopic evidence for both nitrification and denitrification as sources of NO 2 - in a small stream.

Indiana↗

USGS2007

Oxygen isotopes in nitrite: Analysis, calibration, and equilibration

Nitrite is a central intermediate in the nitrogen cycle and can persist in significant concentrations in ocean waters, sediment pore waters, and terrestrial groundwaters. To fully interpret the effect of microbial processes on nitrate (NO 3 - ), nitrite (NO 2 - ), and nitrous oxide (N 2 O) cycling in these systems, the nitrite pool must be accessible to isotopic analysis. Furthermore, because nitrite interferes with most methods of nitrate isotopic analysis, accurate isotopic analysis of nitrite is essential for correct measurement of nitrate isotopes in a sample that contains nitrite. In this study, nitrite salts with varying oxygen isotopic compositions were prepared and calibrated and then used to test the denitrifier method for nitrite oxygen isotopic analysis. The oxygen isotopic fractionation during nitrite reduction to N 2 O by Pseudomonas aureofaciens was lower than for nitrate conversion to N 2 O, while oxygen isotopic exchange between nitrite and water during the reaction was similar. These results enable the extension of the denitrifier method to oxygen isotopic analysis of nitrite (in the absence of nitrate) and correction of nitrate isotopes for the presence of nitrite in “mixed” samples. We tested storage conditions for seawater and freshwater samples that contain nitrite and provide recommendations for accurate oxygen isotopic analysis of nitrite by any method. Finally, we report preliminary results on the equilibrium isotope effect between nitrite and water, which can play an important role in determining the oxygen isotopic value of nitrite where equilibration with water is significant.

Analytical Chemistry↗

USGS2007

Determination of the δ 15 N of nitrate in solids; RSIL lab code 2894

The purpose of the Reston Stable Isotope Laboratory (RSIL) lab code 2894 is to determine the δ 15 N of nitrate (NO 3 - ) 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 δ 15 N of the dissolved NO 3 - is analyzed by conversion of the NO 3 - to nitrous oxide (N 2 O), which serves as the analyte for mass spectrometry. A culture of denitrifying bacteria is used in the enzymatic conversion of NO 3 - to N 2 O, which follows the pathway shown in equation 1: NO 3 - → NO 2 - → NO → 1/2 N 2 O (1) Because the bacteria Pseudomonas aureofaciens lack N 2 O reductive activity, the reaction stops at N 2 O, unlike the typical denitrification reaction that goes to N 2 . After several hours, the conversion is complete, and the N 2 O is extracted from the vial, separated from volatile organic vapor and water vapor by an automated -65 °C isopropanol-slush trap, a Nafion drier, a CO 2 and water removal unit (Costech #021020 carbon dioxide absorbent with Mg(ClO 4 ) 2 ), and trapped in a small-volume trap immersed in liquid nitrogen with a modified Finnigan MAT (now Thermo Scientific) GasBench 2 introduction system. After the N 2 O is released, it is further purified by gas chromatography before introduction to the isotope-ratio mass spectrometer (IRMS). The IRMS is a Thermo Scientific Delta V Plus continuous flow IRMS (CF-IRMS). It has a universal triple collector, consisting of two wide cups with a narrow cup in the middle; it is capable of simultaneously measuring mass/charge ( m/z ) of the N 2 O molecule 44, 45, and 46. The ion beams from these m/z values are as follows: m/z = 44 = N 2 O = 14 N 14 N 16 O; m/z = 45 = N 2 O = 14 N 15 N 16 O or 14 N 14 N 17 O; m/z = 46 = N 2 O = 14 N 14 N 18 O. The 17 O contributions to the m/z 44 and m/z 45 ion beams are accounted for before δ 15 N values are reported.

Techniques and Methods↗

USGS2007

Determination of the δ 15 N and δ 18 O of nitrate in solids; RSIL lab code 2897

The purpose of the Reston Stable Isotope Laboratory (RSIL) lab code 2897 is to determine the δ 15 N and δ 18 O of nitrate (NO 3 - ) in solids. The NO 3 - 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 δ 15 N and δ 18 O of the dissolved NO 3 - is analyzed by conversion of the NO 3 - to nitrous oxide (N 2 O), which serves as the analyte for mass spectrometry. A culture of denitrifying bacteria is used in the enzymatic conversion of NO 3 - to N 2 O, which follows the pathway shown in equation 1: NO 3 - → NO 2 - → NO → 1/2 N 2 O (1) Because the bacteria Pseudomonas aureofaciens lack N 2 O reductive activity, the reaction stops at N 2 O, unlike the typical denitrification reaction that goes to N 2 . After several hours, the conversion is complete, and the N 2 O is extracted from the vial, separated from volatile organic vapor and water vapor by an automated -65 °C isopropanol-slush trap, a Nafion drier, a CO 2 and water removal unit (Costech #021020 carbon dioxide absorbent with Mg(ClO 4 ) 2 ), and trapped in a small-volume trap immersed in liquid nitrogen with a modified Finnigan MAT (now Thermo Scientific) GasBench 2 introduction system. After the N 2 O is released, it is further purified by gas chromatography before introduction to the isotope-ratio mass spectrometer (IRMS). The IRMS is a Thermo Scientific Delta V Plus continuous flow IRMS (CF-IRMS). It has a universal triple collector, consisting of two wide cups with a narrow cup in the middle; it is capable of simultaneously measuring mass/charge ( m/z ) of the N 2 O molecule 44, 45, and 46. The ion beams from these m/z values are as follows: m/z = 44 = N 2 O = 14 N 14 N 16 O; m/z = 45 = N 2 O = 14 N 15 N 16 O or 14 N 14 N 17 O; m/z = 46 = N 2 O = 14 N 14 N 18 O. The 17 O contributions to the m/z 44 and m/z 45 ion beams are accounted for before δ 15 N values are reported.

Techniques and Methods↗

USGS2007

Determination of the δ 15 N of nitrate in water; RSIL lab code 2899

The purpose of the Reston Stable Isotope Laboratory (RSIL) lab code 2899 is to determine the δ 15 N of nitrate (NO 3 - ) in water. The δ 15 N of the dissolved NO 3 - is analyzed by conversion of the NO 3 - to nitrous oxide (N 2 O), which serves as the analyte for mass spectrometry. A culture of denitrifying bacteria is used in the enzymatic conversion of the NO 3 - to N 2 O, which follows the pathway shown in equation 1: NO 3 - → NO 2 - → NO → 1/2 N 2 O (1) Because the bacteria Pseudomonas aureofaciens lack N 2 O reductive activity, the reaction stops at N 2 O, unlike the typical denitrification reaction that goes to N 2 . After several hours, the conversion is complete, and the N 2 O is extracted from the vial, separated from volatile organic vapor and water vapor by an automated -65 °C isopropanol-slush trap, a Nafion drier, a CO 2 and water removal unit (Costech #021020 carbon dioxide absorbent with Mg(ClO 4 ) 2 ), and trapped in a small-volume trap immersed in liquid nitrogen with a modified Finnigan MAT (now Thermo Scientific) GasBench 2 introduction system. After the N 2 O is released, it is further purified by gas chromatography before introduction to the isotope-ratio mass spectrometer (IRMS). The IRMS is a Thermo Scientific Delta V Plus continuous flow IRMS (CF-IRMS). It has a universal triple collector, consisting of two wide cups with a narrow cup in the middle; it is capable of simultaneously measuring mass/charge ( m/z ) of the N 2 O molecule 44, 45, and 46. The ion beams from these m/z values are as follows: m/z = 44 = N 2 O = 14 N 14 N 16 O; m/z = 45 = N 2 O = 14 N 15 N 16 O or 14 N 14 N 17 O; m/z = 46 = N 2 O = 14 N 14 N 18 O. The 17 O contributions to the m/z 44 and m/z 45 ion beams are accounted for before δ 15 N values are reported.

Techniques and Methods↗

USGS2007

Determination of the δ 15 N and δ 18 O of nitrate in water; RSIL lab code 2900

The purpose of the Reston Stable Isotope Laboratory (RSIL) lab code 2900 is to determine the δ 15 N and δ 18 O of nitrate (NO 3 - ) in water. The δ 15 N and δ 18 O of the dissolved NO 3 - are analyzed by converting the NO 3 - to nitrous oxide (N 2 O), which serves as the analyte for mass spectrometry. A culture of denitrifying bacteria is used in the enzymatic conversion of the NO 3 - to N 2 O, which follows the pathway shown in equation 1: NO 3 - → NO 2 - → NO → 1/2 N 2 O (1) Because the bacteria Pseudomonas aureofaciens lack N 2 O reductive activity, the reaction stops at N 2 O, unlike the typical denitrification reaction that goes to N 2 . After several hours, the conversion is complete, and the N 2 O is extracted from the vial, separated from volatile organic vapor and water vapor by an automated -65 °C isopropanol-slush trap, a Nafion drier, a CO 2 and water removal unit (Costech #021020 carbon dioxide absorbent with Mg(ClO 4 ) 2 ), and trapped in a small-volume trap immersed in liquid nitrogen with a modified Finnigan MAT (now Thermo Scientific) GasBench 2 introduction system. After the N 2 O is released, it is further purified by gas chromatography before introduction to the isotope-ratio mass spectrometer (IRMS). The IRMS is a Thermo Scientific Delta V Plus continuous flow IRMS (CF-IRMS). It has a universal triple collector, consisting of two wide cups with a narrow cup in the middle; it is capable of simultaneously measuring mass/charge ( m/z ) of the N 2 O molecule 44, 45, and 46. The ion beams from these m/z values are as follows: m/z = 44 = N 2 O = 14 N 14 N 16 O; m/z = 45 = N 2 O = 14 N 15 N 16 O or 14 N 14 N 17 O; m/z = 46 = N 2 O = 14 N 14 N 18 O. The 17 O contributions to the m/z 44 and m/z 45 ion beams are accounted for before δ 15 N values are reported.

Techniques and Methods↗