A high precision isotope ratio mass spectrometry method for measuring the O{sub 2}/N{sub 2} ratio of air

Journal Article · Tue Nov 01 04:00:00 EST 1994 · Geochimica et Cosmochimica Acta

DOI:https://doi.org/10.1016/0016-7037(94)90205-4· OSTI ID:28582

Bender, M L; Ellis, J T; Orchardo, J ^[1]; Tans, P P ^[2]; Habfast, K ^[3]

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1. Univ. of Rhode Island, Kingston, RI (United States)
2. National Oceanic and Atmospheric Administration, Boulder, CO (United States)
3. Finnigan MAT GmbH, Bremen (Germany)

Studies of the distribution of O{sub 2} in air will inform us about critical problems in the global carbon cycle which are not readily accessed by other measurements, including the rate of seasonal net production in the oceans on a hemispheric scale, the rate at which the oceans are taking up anthropogenic CO{sub 2}, and the net of change of the continental biomass. In this paper, we outline a method for measuring the O{sub 2}/N{sub 2} ratio of air to a standard error of {+-}6 per meg ({+-}0.006{per_thousand}) for a sample analyzed in quadruplicate, corresponding to {+-}1.2 ppmV O{sub 2} in air out of 210,000. The method involves measuring the ratio of {sup 16}O{sub 2} to {sup 15}N{sup 14}N by isotope ratio mass spectrometry. Potential and actual problems with this method include fractionation as sample and reference gases are introduced to the mass spectrometer, mass spectrometric nonlinearity, effects of imbalance of sample and reference ion currents on the measured isotopic ratio, isobaric interferences at masses 28 and 29 due to the formation of CO{sup +} from CO{sub 2} in the source, and zero enrichments. We discuss the magnitude of errors introduced by these factors and outline the relevant corrections. The ultimate mass spectrometric uncertainty is about {+-}2 per meg ({+-}0.4 ppmV) for a 1 h instrumental analysis. Overall precision is currently limited by fractionation as sample and reference gases are introduced into the mass spectrometer. A considerable improvement in precision may be possible.

• OSTI ID: 28582
• Journal Information: Geochimica et Cosmochimica Acta, Journal Name: Geochimica et Cosmochimica Acta Journal Issue: 21 Vol. 58; ISSN GCACAK; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
AIR-WATER INTERACTIONS
CARBON CYCLE
CARBON SINKS
DISTRIBUTION
FEASIBILITY STUDIES
FRACTIONATION
ISOTOPE RATIO
MASS SPECTROSCOPY
NITROGEN
OXYGEN
SEAS
SEASONAL VARIATIONS