<?xml version='1.0' encoding='utf-8'?>
<oai_dc:dc xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:oai_dc="http://www.openarchives.org/OAI/2.0/oai_dc/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.openarchives.org/OAI/2.0/oai_dc/ http://www.openarchives.org/OAI/2.0/oai_dc.xsd">
  <dc:contributor>Danielle S. Boshers</dc:contributor>
  <dc:contributor>J.K. Bohlke</dc:contributor>
  <dc:contributor>Dan Yu</dc:contributor>
  <dc:contributor>Nengwang Chen</dc:contributor>
  <dc:contributor>Craig R. Tobias</dc:contributor>
  <dc:creator>Julie Granger</dc:creator>
  <dc:date>2020</dc:date>
  <dc:description>&lt;h3 id="rcm8569-sec-0001-title" class="article-section__sub-title section1"&gt;Rationale&lt;/h3&gt;&lt;p&gt;The isotope ratios of nitrogen (&lt;sup&gt;15&lt;/sup&gt;N/&lt;sup&gt;14&lt;/sup&gt;N) and oxygen (&lt;sup&gt;18&lt;/sup&gt;O/&lt;sup&gt;16&lt;/sup&gt;O) in nitrite (NO&lt;sub&gt;2&lt;/sub&gt;&lt;sup&gt;−&lt;/sup&gt;) can be measured by conversion of the nitrite into nitrous oxide (N&lt;sub&gt;2&lt;/sub&gt;O) with azide, followed by mass spectrometric analysis of N&lt;sub&gt;2&lt;/sub&gt;O by gas chromatography isotope ratio mass spectrometry (GC/IRMS). While applying this method to brackish samples, we noticed that the N and O isotope ratio measurements of NO&lt;sub&gt;2&lt;/sub&gt;&lt;sup&gt;−&lt;/sup&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;are highly sensitive to sample salinity and to the pH at which samples are preserved.&lt;/p&gt;&lt;h3 id="rcm8569-sec-0002-title" class="article-section__sub-title section1"&gt;Methods&lt;/h3&gt;&lt;p&gt;We investigated the influence of sample salinity and sample preservation pH on the N and O isotope ratios of the N&lt;sub&gt;2&lt;/sub&gt;O produced from the reaction of NO&lt;sub&gt;2&lt;/sub&gt;&lt;sup&gt;−&lt;/sup&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;with azide. The N&lt;sub&gt;2&lt;/sub&gt;O isotope ratios were measured by GC/IRMS.&lt;/p&gt;&lt;h3 id="rcm8569-sec-0003-title" class="article-section__sub-title section1"&gt;Results&lt;/h3&gt;&lt;p&gt;Under the experimental reaction conditions, the conversion of NO&lt;sub&gt;2&lt;/sub&gt;&lt;sup&gt;−&lt;/sup&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;into N&lt;sub&gt;2&lt;/sub&gt;O was less complete in lower salinity solutions, resulting in respective N and O isotopic offsets of +2.5‰ and −14.0‰ compared with seawater solutions. Differences in salinity were also associated with differences in the fraction of O atoms exchanged between NO&lt;sub&gt;2&lt;/sub&gt;&lt;sup&gt;−&lt;/sup&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;and water during the reaction. Similarly, aqueous NO&lt;sub&gt;2&lt;/sub&gt;&lt;sup&gt;−&lt;/sup&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;samples preserved at elevated pH values resulted in the incomplete conversion of NO&lt;sub&gt;2&lt;/sub&gt;&lt;sup&gt;−&lt;/sup&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;into N&lt;sub&gt;2&lt;/sub&gt;O by azide, and consequent pH‐dependent isotopic offsets, as well as differences in the fraction of O atoms exchanged with water. The addition of sodium chloride to the reaction matrix of samples and standards largely mitigated salinity‐dependent isotopic offsets in the N&lt;sub&gt;2&lt;/sub&gt;O product, and nearly homogenized the fraction of O atom exchange among samples of different salinity. A test of the hypobromite–azide method to measure N isotope ratios of ammonium by conversion into NO&lt;sub&gt;2&lt;/sub&gt;&lt;sup&gt;−&lt;/sup&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;then N&lt;sub&gt;2&lt;/sub&gt;O revealed no influence of sample salinity on the N isotope ratios of the N&lt;sub&gt;2&lt;/sub&gt;O product.&lt;/p&gt;&lt;h3 id="rcm8569-sec-0004-title" class="article-section__sub-title section1"&gt;Conclusions&lt;/h3&gt;&lt;p&gt;We outline recommendations to mitigate potential matrix effects among samples and standards, to improve the accuracy of N and O isotope ratios in NO&lt;sub&gt;2&lt;/sub&gt;&lt;sup&gt;−&lt;/sup&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;measured with the azide method.&lt;/p&gt;</dc:description>
  <dc:format>application/pdf</dc:format>
  <dc:identifier>10.1002/rcm.8569</dc:identifier>
  <dc:language>en</dc:language>
  <dc:publisher>Wiley</dc:publisher>
  <dc:title>The influence of sample matrix on the accuracy of nitrite N and O isotope ratio analyses with the azide method</dc:title>
  <dc:type>article</dc:type>
</oai_dc:dc>