The absolute δ18 O value for SLAP with respect to VSMOW reveals a much lower value than previously established.
Rapid Commun Mass Spectrom
; 38(6): e9678, 2024 Mar 30.
Article
em En
| MEDLINE
| ID: mdl-38356090
ABSTRACT
RATIONALE SLAP is one of the two calibration materials for the isotopic water scale. By consensus the established δ18 O value is -55.5, although several expert laboratories measure significantly more negative δ18 OSLAP values. The real δ18 OSLAP value as such does not influence the isotopic water scale; however, knowledge of the size of isotopic scale contraction in stable isotope measurements is vital for second-order isotopes. This study describes the quantification of δ18 OSLAP with respect to δ18 OVSMOW . METHODS:
SLAP-like water was quantitatively mixed with highly 18 O-enriched water to mimic VSMOW. The 18 O concentration was determined using an electron ionization quadrupole mass spectrometer. The isotopic composition of the SLAP-like and VSMOW-like waters was measured using an optical spectrometer, alongside original VSMOW and SLAP.RESULTS:
This study resulted in a much more negative δ18 O value for SLAP than expected. The averaged outcome of seven independent experiments is δ18 OSLAP = -56.33 ± 0.03. There is a large discrepancy between the actual isotopic measurements of even the most carefully operating isotope laboratories and the true δ18 O value.CONCLUSIONS:
Although this finding as such does not influence the use of the VSMOW-SLAP scale, it raises the intriguing question of what we actually measure with our instruments and why even a fully corrected measurement can be so far off. Our result has consequences for issues like the transfer of δ18 O from and to the VPDB scale, various fractionation factors, and Δ17 O. The absolute 18 O abundance for SLAP was calculated as (1887.98 ± 0.43) × 10-6 based on the absolute 18 O abundance of VSMOW and the presented δ18 OSLAP in this paper.
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Coleções:
01-internacional
Base de dados:
MEDLINE
Idioma:
En
Ano de publicação:
2024
Tipo de documento:
Article