Comparison of δ18O measurements in nitrate by different combustion techniques
Analytical Chemistry
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Abstract
Three different KNO3 salts with δ18O values ranging from about −31 to +54‰ relative to VSMOW were used to compare three off-line, sealed glass tube combustion methods (widely used for isotope studies) with a more recently developed on-line carbon combustion technique. All methods yielded roughly similar isotope ratios for KNO3 samples with δ18O values in the midpoint of the δ18O scale near that of the nitrate reference material IAEA-NO-3 (around +21 to +25‰). This reference material has been used previously for one-point interlaboratory and intertechnique calibrations. However, the isotope ratio scale factors by all of the off-line combustion techniques are compressed such that they are between 0.3 and 0.7 times that of the on-line combustion technique. The contraction of the δ18O scale in the off-line preparations apparently is caused by O isotope exchange between the sample and the glass combustion tubes. These results reinforce the need for nitrate reference materials with δ18O values far from that of atmospheric O2, to improve interlaboratory comparability.
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Comparison of δ18O measurements in nitrate by different combustion techniques |
| Series title | Analytical Chemistry |
| DOI | 10.1021/ac025854b |
| Volume | 74 |
| Issue | 20 |
| Year Published | 2002 |
| Language | English |
| Publisher | American Chemical Society |
| Contributing office(s) | Toxic Substances Hydrology Program |
| Description | 4 p. |
| First page | 5410 |
| Last page | 5413 |
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