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1.
Environ Sci Technol ; 47(3): 1478-86, 2013 Feb 05.
Artículo en Inglés | MEDLINE | ID: mdl-23240620

RESUMEN

The capacity to make in situ geo-referenced measurements of methane concentration and stable isotopic composition (δ(13)C(CH4)) would greatly improve our understanding of the distribution and type of methane sources in the environment, allow refined determination of the extent to which microbial production and consumption contributes to methane cycling, and enable the testing of hypotheses about the sensitivity of methane cycling to changes in environmental conditions. In particular, characterizing biogeochemical methane cycling dynamics in the deep ocean is hampered by a number of challenges, especially in environments where high methane concentrations preclude intact recovery of undisturbed samples. To that end, we have developed an in situ analyzer capable of δ(13)C(CH4) measurements in the deep ocean. Here we present data from laboratory and field studies in which we characterize the instrument's analytical capabilities and performance and provide the first in situ stable isotope based characterization of the influence of anaerobic methane oxidation on methane flux from seep sediments. These data illustrate how in situ measurements can permit finer-scale analyses of variations in AOM activity, and facilitate advances in using δ(13)C(CH4) and other isotopic systems to interrogate biogeochemical cycles in the deep sea and other remote or challenging environments.


Asunto(s)
Marcaje Isotópico/métodos , Metano/análisis , Agua de Mar/química , Calibración , Isótopos de Carbono , Presión Hidrostática , Reología , Soluciones , Temperatura
2.
Appl Opt ; 44(31): 6712-7, 2005 Nov 01.
Artículo en Inglés | MEDLINE | ID: mdl-16270560

RESUMEN

An autonomous instrument based on off-axis integrated cavity output spectroscopy has been developed and successfully deployed for measurements of carbon monoxide in the troposphere and tropopause onboard a NASA DC-8 aircraft. The instrument (Carbon Monoxide Gas Analyzer) consists of a measurement cell comprised of two high-reflectivity mirrors, a continuous-wave quantum-cascade laser, gas sampling system, control and data-acquisition electronics, and data-analysis software. CO measurements were determined from high-resolution CO absorption line shapes obtained by tuning the laser wavelength over the R(7) transition of the fundamental vibration band near 2172.8 cm(-1). The instrument reports CO mixing ratio (mole fraction) at a 1-Hz rate based on measured absorption, gas temperature, and pressure using Beer's Law. During several flights in May-June 2004 and January 2005 that reached altitudes of 41,000 ft (12.5 km), the instrument recorded CO values with a precision of 0.2 ppbv (1-s averaging time) and an accuracy limited by the reference CO gas cylinder (uncertainty < 1.0%). Despite moderate turbulence and measurements of particulate-laden airflows, the instrument operated consistently and did not require any maintenance, mirror cleaning, or optical realignment during the flights.

3.
Anal Chem ; 74(9): 2003-7, 2002 May 01.
Artículo en Inglés | MEDLINE | ID: mdl-12033299

RESUMEN

We have constructed a cavity ring-down spectrometer employing a near-IR external cavity diode laser capable of measuring 13C/12C isotopic ratios in CO2 in human breath. The system, which has a demonstrated minimum detectable absorption loss of 3.2 x 10(-11) cm(-1) Hz(-1/2), determines the isotopic ratio of 13C16O16O/12C16O16O by measuring the intensities of rotationally resolved absorption features of each species. As in isotope ratio mass spectrometry (IRMS), the isotopic ratio of a sample is compared to that of a standard CO2 sample calibrated to the Pee Dee Belemnite scale and reported as the sample's delta13C value. Measurements of eight replicate CO2 samples standardized by IRMS and consisting of 5% CO2 in N2 at atmospheric pressure demonstrated a precision of 0.22/1000 for the technique. Delta13C values were also obtained for breath samples from individuals testing positive and negative for the presence of Helicobacter pylori, the leading cause of peptic ulcers in humans. This study demonstrates the ability of the instrument to obtain delta13C values in breath samples with sufficient precision to serve as a useful medical diagnostic.


Asunto(s)
Pruebas Respiratorias/métodos , Dióxido de Carbono/análisis , Isótopos de Carbono , Espectroscopía Infrarroja por Transformada de Fourier/métodos , Pruebas Respiratorias/instrumentación , Equipo para Diagnóstico , Infecciones por Helicobacter/diagnóstico , Humanos , Rayos Láser , Respiración , Espectroscopía Infrarroja por Transformada de Fourier/instrumentación
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