Joel Savarino J.K. Böhlke Mark Thiemens Greg Michalski 2002 <p><span>A thermal decomposition method was developed and tested for the simultaneous determination of δ</span>¹⁸<span>O and δ</span>¹⁷<span>Ο in nitrate. The thermal decomposition of AgNO</span>₃<span> allows for the rapid and accurate determination of </span>¹⁸<span>O/</span>¹⁶<span>O and </span>¹⁷<span>O/</span>¹⁶<span>O isotopic ratios with a precision of ±1.5‰ for δ</span>¹⁸<span>O and ±0.11‰ for Δ</span>¹⁷<span>Ο (Δ</span>¹⁷<span>Ο = δ</span>¹⁷<span>Ο − 0.52 × δ</span>¹⁸<span>O). The international nitrate isotope reference material IAEA-NO3 yielded a δ</span>¹⁸<span>O value of +23.6‰ and Δ</span>¹⁷<span>Ο of −0.2‰, consistent with normal terrestrial mass-dependent isotopic ratios. In contrast, a large sample of NaNO</span>₃<span> from the Atacama Desert, Chile, was found to have Δ</span>¹⁷<span>Ο = 21.56 ± 0.11‰ and δ</span>¹⁸<span>O = 54.9 ± 1.5‰, demonstrating a substantial mass-independent isotopic composition consistent with the proposed atmospheric origin of the desert nitrate. It is suggested that this sample (designated USGS-35) can be used to generate other gases (CO</span>₂<span>, CO, N</span>₂<span>O, O</span>₂<span>) with the same Δ</span>¹⁷<span>Ο to serve as measurement references for a variety of applications involving mass-independent isotopic compositions in environmental studies.</span></p> application/pdf 10.1021/ac0256282 en American Chemical Society Determination of the total oxygen isotopic composition of nitrate and the calibration of a Δ17Ο nitrate reference material article