Analysis of oxygen‐17 excess of nitrate and sulfate at sub‐micromole levels using the pyrolysis method. (1st October 2013)

• Record Type: Journal Article
• Authors: Geng, Lei; Schauer, Andrew J.; Kunasek, Shelley A.; Sofen, Eric D.; Erbland, Joseph; Savarino, Joël; Allman, Daniel J.; Sletten, Ronald S.; Alexander, Becky
• Is Part Of: Rapid communications in mass spectrometry. Volume 27:Number 21(2013)
• Page Start: 2411
• Page End: 2419
• Publication Date: 2013-10-01
• Subjects: Mass spectrometry -- Periodicals; 543.65
• DOI: 10.1002/rcm.6703
• Languages: English
• ISSNs: 0951-4198

Abstract

<abstract abstract-type="main"> <title> <x xml:space="preserve">Abstract</x> </title> <sec id="rcm6703-sec-0001" sec-type="section"> <title>RATIONALE</title> <p>The oxygen‐17 excess (Δ<sup>17</sup>O) of nitrate and sulfate contains valuable information regarding their atmospheric formation pathways. However, the current pyrolysis method to measure Δ<sup>17</sup>O requires large sample amounts (>4 µmol for nitrate and >1 µmol for sulfate). We present a new approach employing a Gas Bench interface which cryofocuses O<sub>2</sub> produced from sample pyrolysis, enabling the analysis of sub‐micromole size samples.</p> </sec> <sec id="rcm6703-sec-0002" sec-type="section"> <title>METHODS</title> <p>Silver nitrate or sulfate at sub‐micromole levels in a sample container was thermally decomposed to O<sub>2</sub> and byproducts in a modified Temperature Conversion/Elemental Analyzer (TC/EA). Byproducts (mainly NO<sub>2</sub> for silver nitrate and SO<sub>2</sub> for silver sulfate) were removed in a liquid nitrogen trap and the sample O<sub>2</sub> was carried by ultra‐pure helium (He) gas to a Gas Bench II interface where it was cryofocused prior to entering an isotope ratio mass spectrometer.</p> </sec> <sec id="rcm6703-sec-0003" sec-type="section"> <title>RESULTS</title> <p>Analysis of the international nitrate reference material USGS35 (Δ<sup>17</sup>O = 21.6‰) within the size range of 300–1000 nmol O<sub>2</sub> gave a mean Δ<sup>17</sup>O value of (21.6 ± 0.69) ‰ (mean ±1σ). Three inter‐laboratory calibrated sulfate reference materials, Sulf‐α, Sulf‐β and Sulf‐ε, each within the size range of 180–1000 nmol O<sub>2</sub>, were analyzed and shown to possess mean Δ<sup>17</sup>O values of (0.9 ± 0.10) ‰, (2.1 ± 0.25) ‰ and (7.0 ± 0.63) ‰, respectively.</p> </sec> <sec id="rcm6703-sec-0004" sec-type="section"> <title>CONCLUSIONS</title> <p>The analyses of nitrate and sulfate reference materials at sub‐micromole levels gave Δ<sup>17</sup>O values consistent with their accepted values. This new approach of employing the Gas Bench to cryofocus O<sub>2</sub> after the pyrolysis of AgNO<sub>3</sub> and Ag<sub>2</sub>SO<sub>4</sub> particularly benefits the effort of measuring Δ<sup>17</sup>O in sample types with a low abundance of nitrate and sulfate such as ice cores. Copyright © 2013 John Wiley & Sons, Ltd.</p> </sec> </abstract>