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Willi A Brand - One of the best experts on this subject based on the ideXlab platform.
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preliminary assessment of stable nitrogen and oxygen isotopic composition of usgs51 and usgs52 nitrous oxide Reference Gases and perspectives on calibration needs
Rapid Communications in Mass Spectrometry, 2018Co-Authors: Nathaniel E Ostrom, Karen L Casciotti, Willi A Brand, Sakae Toyoda, Hasand Gandhi, Tyler B Coplen, J K Bohlke, Jens Dyckmans, Anette Giesemann, Joachim MohnAbstract:Rationale Despite a long history and growing interest in isotopic analyses of N2 O, there is a lack of isotopically characterized N2 O isotopic Reference materials (standards) to enable normalization and reporting of isotope-delta values. Here we report the isotopic characterization of two pure N2 O Gas Reference materials, USGS51 and USGS52, which are now available for laboratory calibration (https://isotopes.usgs.gov/lab/Referencematerials.html). Methods A total of 400 sealed borosilicate glass tubes of each N2 O Reference Gas were prepared from a single Gas filling of a high vacuum line. We demonstrated isotopic homogeneity via dual-inlet isotope-ratio mass spectrometry. Isotopic analyses of these Reference materials were obtained from eight laboratories to evaluate interlaboratory variation and provide preliminary isotopic characterization of their δ15 N, δ18 O, δ15 Nα , δ15 Nβ and site pReference (SP ) values. Results The isotopic homogeneity of both USGS51 and USGS52 was demonstrated by one-sigma standard deviations associated with the determinations of their δ15 N, δ18 O, δ15 Nα , δ15 Nβ and SP values of 0.12 mUr or better. The one-sigma standard deviations of SP measurements of USGS51 and USGS52 reported by eight laboratories participating in the interlaboratory comparison were 1.27 and 1.78 mUr, respectively. Conclusions The agreement of isotope-delta values obtained in the interlaboratory comparison was not sufficient to provide reliable accurate isotope measurement values for USGS51 and USGS52. We propose that provisional values for the isotopic composition of USGS51 and USGS52 determined at the Tokyo Institute of Technology can be adopted for normalizing and reporting sample data until further refinements are achieved through additional calibration efforts.
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automated simultaneous measurement of the δ13c and δ2h values of methane and the δ13c and δ18o values of carbon dioxide in flask air samples using a new multi cryo trap Gas chromatography isotope ratio mass spectrometry system
Rapid Communications in Mass Spectrometry, 2016Co-Authors: Willi A Brand, Michael Rothe, Peter Sperlich, Martin Strube, Magnus WendebergAbstract:RATIONALE The isotopic composition of greenhouse Gases helps to constrain global budgets and to study sink and source processes. We present a new system for high-precision stable isotope measurements of carbon, hydrogen and oxygen in atmospheric methane and carbon dioxide. The design is intended for analyzing flask air samples from existing sampling programs without the need for extra sample air for methane analysis. METHODS CO2 and CH4 isotopes are measured simultaneously using two isotope ratio mass spectrometers, one for the analysis of δ(13) C and δ(18) O values and the second one for δ(2) H values. The inlet carousel delivers air from 16 sample positions (glass flasks 1-5 L and high-pressure cylinders). Three 10-port valves take aliquots from the sample stream. CH4 from 100-mL air aliquots is preconcentrated in 0.8-mL sample loops using a new cryo-trap system. A precisely calibrated working Reference air is used in parallel with the sample according to the Principle of Identical Treatment. RESULTS It takes about 36 hours for a fully calibrated analysis of a complete carousel including extractions of four working Reference and one quality control Reference air. Long-term precision values, as obtained from the quality control Reference Gas since 2012, account for 0.04 ‰ (δ(13) C values of CO2 ), 0.07 ‰ (δ(18) O values of CO2 ), 0.11 ‰ (δ(13) C values of CH4 ) and 1.0 ‰ (δ(2) H values of CH4 ). Within a single day, the system exhibits a typical methane δ(13) C standard deviation (1σ) of 0.06 ‰ for 10 repeated measurements. CONCLUSIONS The system has been in routine operation at the MPI-BGC since 2012. Consistency of the data and compatibility with results from other laboratories at a high precision level are of utmost importance. A high sample throughput and reliability of operation are important achievements of the presented system to cope with the large number of air samples to be analyzed. Copyright © 2016 John Wiley & Sons, Ltd.
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improved isotope ratio measurement performance in liquid chromatography isotope ratio mass spectrometry by removing excess oxygen
Rapid Communications in Mass Spectrometry, 2007Co-Authors: Elena Hettmann, Willi A Brand, Gerd GleixnerAbstract:A low dead volume oxygen scrubbing system was introduced in a commercially available liquid chromatography/isotope ratio mass spectrometry (LC/IRMS) interface to enhance the analytical capability of the system. In the LC/IRMS interface carbon from organic samples is converted into CO(2) inside the mobile phase by wet chemical oxidation using peroxodisulfate (Na(2)S(2)O(8)). After passing the hot reaction zone, surplus oxygen (O(2)) remains dissolved in the liquid phase. Both CO(2) and O(2) diffuse through a transfer membrane into the helium carrier and are transferred to the mass spectrometer. The presence of O(2) in the ion source may have detrimental effects on measurement accuracy and precision as well as on filament lifetime. As a remedy, a new on-line O(2)-removing device has been incorporated into the system. The new O(2) scrubber consists of two parallel hot copper reduction reactors (0.8 mm i.d., active length 120 mm) and a switch-over valve between them. One reactor is regenerated using He/H(2) while the other is actively scavenging O(2) from the Gas stream. The capacity of each reduction reactor, expressed as usage time, is between 40 and 50 min. This is sufficient for a single LC run for sugars and organic acids. A further increase of the reduction capacity is accompanied by a peak broadening of about 100%. After switching to a freshly reduced reactor the oxygen background and the delta(13)C values of the Reference Gas need up to 500 s to stabilize. For repeated injections the delta(13)C values of sucrose remain constant (+/-0.1 per thousand) for about 3000 s. The long-term stability for measurements of sucrose was 0.11 per thousand without the reduction oven and improved slightly to 0.08 per thousand with the reduction oven. The filament lifetime improved by more than 600%, thereby improving the long-term system stability and analytical efficiency. In addition the costs per analysis were reduced considerably.
C Charoenpong - One of the best experts on this subject based on the ideXlab platform.
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a continuous flow isotope ratio mass spectrometry method for high precision determination of dissolved Gas ratios and isotopic composition
Limnology and Oceanography-methods, 2014Co-Authors: C Charoenpong, Laura A Bristow, Mark A AltabetAbstract:Dissolved Gas ratios and isotopic compositions provide essential information about the biological and physical mechanisms influencing N2, O2, and Ar in aquatic systems. Current methods available are either limited by overall cost, labor-intensive sample collection and analysis, or insufficient precision. Here, we present a new highly accurate and robust method for sample collection and subsequent simultaneous measurement of the dissolved Gas ratios (N2/Ar and O2/Ar) and isotopic compositions (δ15N2 and δ18O2) in seawater. The relatively simple sampling procedure using low cost materials enables collection of hundreds to more than a thousand discrete samples on a single research cruise. Samples can be preserved and stored at room temperature and maintain their integrity for many months. Laboratory analysis employs an on-line extraction system coupled to a multi-collector isotope ratio mass spectrometer (IRMS). A continuous flow of He carrier Gas completely deGasses the sample, and passes through the preparation and purification system before entering the IRMS for analysis. The use of this continuous He carrier permits short analysis times (less than 8 min per sample) as compared with current high-precision methods. In addition to Reference Gases, calibration is achieved using air-equilibrated water standards of known temperature and salinity. Assessment of Reference Gas injections, air equilibrated standards, as well as samples collected in the field shows the accuracy and precision of this new method to be equal to or better than current standard techniques.
Nadia Elfarhan - One of the best experts on this subject based on the ideXlab platform.
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method specific serum cortisol responses to the adrenocorticotrophin test comparison of Gas chromatography mass spectrometry and five automated immunoassays
Clinical Endocrinology, 2013Co-Authors: Nadia Elfarhan, Alan Pickett, David Ducroq, Catherine Bailey, Kelly Mitchem, Nicola Morgan, Annie Armston, Laila Jones, Carol EvansAbstract:Objective: The serum cortisol response to the ACTH test is known to vary significantly by assay but lower Reference limits (LRL) for this response have not been established by the Reference Gas chromatography-mass spectrometry (GC-MS) method or modern immunoassays. We aimed to compare the normal cortisol response to ACTH stimulation using GC-MS with five widely used immunoassays. Design, Patients and Measurements: An ACTH test (250 micrograms iv ACTH1-24) was undertaken in 165 healthy volunteers (age 20-66yrs; 105 female, 24 of whom were taking an oestrogencontaining oral contraceptive pill [OCP]). Serum cortisol was measured using GC-MS, Advia Centaur (Siemens), Architect (Abbott), Modular Analytics E170 (Roche), Immulite 2000 (Siemens) and Access (Beckman) automated immunoassays. The estimated LRL for the 30min cortisol response to ACTH was derived from the 2.5th percentile of log-transformed concentrations. Results: The GC-MS-measured cortisol response was normally distributed in males but not females, with no significant gender difference in baseline or post-ACTH cortisol concentration. Immunoassays were positively biased relative to GC-MS, except in samples from women on the OCP, who showed a consistent negative bias. The LRL for cortisol was method-specific (GC-MS: 420 nmol/l; Architect: 430 nmol/l; Centaur: 446 nmol/l; Access 459 nmol/l; Immulite (2000) 474 nmol/l) and, for the E170, also gender-specific (Female: 524 nmol/l; Male 574 nmol/l). A separate LRL is necessary for women on the OCP. Conclusions: Normal cortisol responses to the ACTH test are influenced significantly by assay and oestrogen treatment. We recommend the use of separate Reference limits in premenopausal women on the OCP, and warn users that cortisol measurements in this subgroup are subject to assay interference.
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method specific serum cortisol responses to the adrenocorticotrophin test comparison of Gas chromatography mass spectrometry and five automated immunoassays
Clinical Endocrinology, 2013Co-Authors: Nadia Elfarhan, Alan Pickett, David Ducroq, Catherine Bailey, Kelly Mitchem, Nicola Morgan, Annie Armston, Laila Jones, Carol Evans, Aled D ReesAbstract:Objective: The serum cortisol response to the ACTH test is known to vary significantly by assay but lower Reference limits (LRL) for this response have not been established by the Reference Gas chromatography-mass spectrometry (GC-MS) method or modern immunoassays. We aimed to compare the normal cortisol response to ACTH stimulation using GC-MS with five widely used immunoassays. Design, Patients and Measurements: An ACTH test (250 micrograms iv ACTH1-24) was undertaken in 165 healthy volunteers (age 20-66yrs; 105 female, 24 of whom were taking an oestrogencontaining oral contraceptive pill [OCP]). Serum cortisol was measured using GC-MS, Advia Centaur (Siemens), Architect (Abbott), Modular Analytics E170 (Roche), Immulite 2000 (Siemens) and Access (Beckman) automated immunoassays. The estimated LRL for the 30min cortisol response to ACTH was derived from the 2.5th percentile of log-transformed concentrations. Results: The GC-MS-measured cortisol response was normally distributed in males but not females, with no significant gender difference in baseline or post-ACTH cortisol concentration. Immunoassays were positively biased relative to GC-MS, except in samples from women on the OCP, who showed a consistent negative bias. The LRL for cortisol was method-specific (GC-MS: 420 nmol/l; Architect: 430 nmol/l; Centaur: 446 nmol/l; Access 459 nmol/l; Immulite (2000) 474 nmol/l) and, for the E170, also gender-specific (Female: 524 nmol/l; Male 574 nmol/l). A separate LRL is necessary for women on the OCP. Conclusions: Normal cortisol responses to the ACTH test are influenced significantly by assay and oestrogen treatment. We recommend the use of separate Reference limits in premenopausal women on the OCP, and warn users that cortisol measurements in this subgroup are subject to assay interference.
Sakae Toyoda - One of the best experts on this subject based on the ideXlab platform.
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preliminary assessment of stable nitrogen and oxygen isotopic composition of usgs51 and usgs52 nitrous oxide Reference Gases and perspectives on calibration needs
Rapid Communications in Mass Spectrometry, 2018Co-Authors: Nathaniel E Ostrom, Karen L Casciotti, Willi A Brand, Sakae Toyoda, Hasand Gandhi, Tyler B Coplen, J K Bohlke, Jens Dyckmans, Anette Giesemann, Joachim MohnAbstract:Rationale Despite a long history and growing interest in isotopic analyses of N2 O, there is a lack of isotopically characterized N2 O isotopic Reference materials (standards) to enable normalization and reporting of isotope-delta values. Here we report the isotopic characterization of two pure N2 O Gas Reference materials, USGS51 and USGS52, which are now available for laboratory calibration (https://isotopes.usgs.gov/lab/Referencematerials.html). Methods A total of 400 sealed borosilicate glass tubes of each N2 O Reference Gas were prepared from a single Gas filling of a high vacuum line. We demonstrated isotopic homogeneity via dual-inlet isotope-ratio mass spectrometry. Isotopic analyses of these Reference materials were obtained from eight laboratories to evaluate interlaboratory variation and provide preliminary isotopic characterization of their δ15 N, δ18 O, δ15 Nα , δ15 Nβ and site pReference (SP ) values. Results The isotopic homogeneity of both USGS51 and USGS52 was demonstrated by one-sigma standard deviations associated with the determinations of their δ15 N, δ18 O, δ15 Nα , δ15 Nβ and SP values of 0.12 mUr or better. The one-sigma standard deviations of SP measurements of USGS51 and USGS52 reported by eight laboratories participating in the interlaboratory comparison were 1.27 and 1.78 mUr, respectively. Conclusions The agreement of isotope-delta values obtained in the interlaboratory comparison was not sufficient to provide reliable accurate isotope measurement values for USGS51 and USGS52. We propose that provisional values for the isotopic composition of USGS51 and USGS52 determined at the Tokyo Institute of Technology can be adopted for normalizing and reporting sample data until further refinements are achieved through additional calibration efforts.
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determination of nitrogen isotopomers of nitrous oxide on a modified isotope ratio mass spectrometer
Analytical Chemistry, 1999Co-Authors: Sakae Toyoda, Naohiro YoshidaAbstract:A new method for the determination of the nitrogen isotopomers (intramolecular distribution of the nitrogen isotopes) of nitrous oxide has been developed. The method makes use of mass analyses of the molecular (N2O+) and fragment (NO+) ions of N2O on an isotope-ratio mass spectrometer equipped with a special ion collector system. The fragmentation of N2O in the electron impact ion source is fairly stable, and the precision of isotope ratio measurements of the fragment ion relative to the Reference Gas is better than 0.1‰ for pure N2O samples introduced from a conventional dual-inlet system. Although it is found that the observed isotope ratio of the fragment ion is affected by rearrangement reactions in the ion source, a correction can be applied using an experimentally determined rearrangement fraction. Calibration of the standard N2O for isotopomer measurements is performed by two procedures: (1) preparation of an N2O standard by thermal decomposition of NH4NO3, (2) relative measurements with pure NO.
Karen L Casciotti - One of the best experts on this subject based on the ideXlab platform.
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preliminary assessment of stable nitrogen and oxygen isotopic composition of usgs51 and usgs52 nitrous oxide Reference Gases and perspectives on calibration needs
Rapid Communications in Mass Spectrometry, 2018Co-Authors: Nathaniel E Ostrom, Karen L Casciotti, Willi A Brand, Sakae Toyoda, Hasand Gandhi, Tyler B Coplen, J K Bohlke, Jens Dyckmans, Anette Giesemann, Joachim MohnAbstract:Rationale Despite a long history and growing interest in isotopic analyses of N2 O, there is a lack of isotopically characterized N2 O isotopic Reference materials (standards) to enable normalization and reporting of isotope-delta values. Here we report the isotopic characterization of two pure N2 O Gas Reference materials, USGS51 and USGS52, which are now available for laboratory calibration (https://isotopes.usgs.gov/lab/Referencematerials.html). Methods A total of 400 sealed borosilicate glass tubes of each N2 O Reference Gas were prepared from a single Gas filling of a high vacuum line. We demonstrated isotopic homogeneity via dual-inlet isotope-ratio mass spectrometry. Isotopic analyses of these Reference materials were obtained from eight laboratories to evaluate interlaboratory variation and provide preliminary isotopic characterization of their δ15 N, δ18 O, δ15 Nα , δ15 Nβ and site pReference (SP ) values. Results The isotopic homogeneity of both USGS51 and USGS52 was demonstrated by one-sigma standard deviations associated with the determinations of their δ15 N, δ18 O, δ15 Nα , δ15 Nβ and SP values of 0.12 mUr or better. The one-sigma standard deviations of SP measurements of USGS51 and USGS52 reported by eight laboratories participating in the interlaboratory comparison were 1.27 and 1.78 mUr, respectively. Conclusions The agreement of isotope-delta values obtained in the interlaboratory comparison was not sufficient to provide reliable accurate isotope measurement values for USGS51 and USGS52. We propose that provisional values for the isotopic composition of USGS51 and USGS52 determined at the Tokyo Institute of Technology can be adopted for normalizing and reporting sample data until further refinements are achieved through additional calibration efforts.
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Fully automated system for stable isotopic analyses of dissolved nitrous oxide at natural abundance levels
Limnology and Oceanography: Methods, 2010Co-Authors: Matthew R. Mcilvin, Karen L CasciottiAbstract:Isotopic and isotopomeric analyses of dissolved nitrous oxide (N2 O) can provide important information about the mechanisms of production and consumption of this climatically important trace Gas. Increased spa- tial and temporal data coverage for N2 O isotopicmeasurements are needed to improve our understanding of the production of N2 O in a variety of aquatic environments, such as coastal and open ocean areas. A new method is presented for automated measurement of δ15 Nbulk , δ18 O, and site pReference of dissolved nitrous oxide in nat- ural waters using a GC-Pal autosampler and a Finnigan DeltaPlus isotope ratio mass spectrometer and is capable of analyzing 30 samples in 22 h without user attention after the start of the run. The system was first tested with samples produced by injecting our N2 O Reference Gas and/or N2 O test mixtures, ranging in isotopic com- position and concentration, into N2 -sparged seawater. The method was then applied to samples containing a large range of N2O concentrations, δ15 Nbulk , δ18 O, and site pReference values fromtwo high-resolution depth pro- files from the Arabian Sea. The results showed precise determination of isotopic values of N2 O from 160 mL aqueous samples over the concentration range normally found in the oceans (5-80 nmol L–1 ). Sample standard deviation for triplicate 160 mL samples at 6 nmol L–1 N2O is better than 0.3‰for δ15 Nbulk , 0.5‰for δ18 O, and 1.0‰for 15 N site pReference. The automated technique described here requires relatively minor modifications of existing N2 O purge and trap systems and can be implemented broadly for a variety of applications.