<?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>Tyler B. Coplen</dc:contributor>
  <dc:contributor>Leonard I Wassenaar</dc:contributor>
  <dc:creator>Haiping Qi</dc:creator>
  <dc:date>2011</dc:date>
  <dc:description>&lt;div class="article-section__content en main"&gt;&lt;p&gt;It is well known that N&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;in the ion source of a mass spectrometer interferes with the CO background during the&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;i&gt;δ&lt;/i&gt;&lt;sup&gt;18&lt;/sup&gt;O measurement of carbon monoxide. A similar problem arises with the high‐temperature conversion (HTC) analysis of nitrogenous O‐bearing samples (e.g. nitrates and keratins) to CO for&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;i&gt;δ&lt;/i&gt;&lt;sup&gt;18&lt;/sup&gt;O measurement, where the sample introduces a significant N&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;peak before the CO peak, making determination of accurate oxygen isotope ratios difficult. Although using a gas chromatography (GC) column longer than that commonly provided by manufacturers (0.6 m) can improve the efficiency of separation of CO and N&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;and using a valve to divert nitrogen and prevent it from entering the ion source of a mass spectrometer improved measurement results, biased&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;i&gt;δ&lt;/i&gt;&lt;sup&gt;18&lt;/sup&gt;O values could still be obtained. A careful evaluation of the performance of the GC separation column was carried out. With optimal GC columns, the&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;i&gt;δ&lt;/i&gt;&lt;sup&gt;18&lt;/sup&gt;O reproducibility of human hair keratins and other keratin materials was better than ±0.15 ‰ (n = 5; for the internal analytical reproducibility), and better than ±0.10 ‰ (n = 4; for the external analytical reproducibility).&amp;nbsp;&lt;/p&gt;&lt;/div&gt;</dc:description>
  <dc:format>application/pdf</dc:format>
  <dc:identifier>10.1002/rcm.5088</dc:identifier>
  <dc:language>en</dc:language>
  <dc:publisher>Wiley</dc:publisher>
  <dc:title>Improved online δ18O measurements of nitrogen‐ and sulfur‐bearing organic materials and a proposed analytical protocol</dc:title>
  <dc:type>article</dc:type>
</oai_dc:dc>