Improved accuracy and precision in δ15NAIR measurements of explosives, urea, and inorganic nitrates by elemental analyzer/isotope ratio mass spectrometry using thermal decomposition. (30th June 2015)

• Record Type: Journal Article
• Authors: Lott, Michael J.; Howa, John D.; Chesson, Lesley A.; Ehleringer, James R.
• Is Part Of: Rapid communications in mass spectrometry. Volume 29:Number 15(2015)
• Page Start: 1381
• Page End: 1388
• Publication Date: 2015-06-30
• Subjects: Mass spectrometry -- Periodicals; 543.65
• DOI: 10.1002/rcm.7229
• Languages: English
• ISSNs: 0951-4198

Abstract

<abstract abstract-type="main"> <title> <x xml:space="preserve">Abstract</x> </title> <sec id="rcm7229-sec-0001" sec-type="section"> <title>Rationale</title> <p>Elemental analyzer systems generate N<sub>2</sub> and CO<sub>2</sub> for elemental composition and isotope ratio measurements. As quantitative conversion of nitrogen in some materials (i.e., nitrate salts and nitro‐organic compounds) is difficult, this study tests a recently published method – thermal decomposition without the addition of O<sub>2</sub> – for the analysis of these materials.</p> </sec> <sec id="rcm7229-sec-0002" sec-type="section"> <title>Methods</title> <p>Elemental analyzer/isotope ratio mass spectrometry (EA/IRMS) was used to compare the traditional combustion method (CM) and the thermal decomposition method (TDM), where additional O<sub>2</sub> is eliminated from the reaction. The comparisons used organic and inorganic materials with oxidized and/or reduced nitrogen and included ureas, nitrate salts, ammonium sulfate, nitro esters, and nitramines. Previous TDM applications were limited to nitrate salts and ammonium sulfate. The measurement precision and accuracy were compared to determine the effectiveness of converting materials containing different fractions of oxidized nitrogen into N<sub>2</sub>.</p> </sec> <sec id="rcm7229-sec-0003" sec-type="section"> <title>Results</title> <p>The <italic>δ</italic><sup>13</sup>C<sub>VPDB</sub> values were not meaningfully different when measured via CM or TDM, allowing for the analysis of multiple elements in one sample. For materials containing oxidized nitrogen, <sup>15</sup>N measurements made using thermal decomposition were more precise than those made using combustion. The precision was similar between the methods for materials containing reduced nitrogen. The %N values were closer to theoretical when measured by TDM than by CM. The <italic>δ</italic><sup>15</sup>N<sub>AIR</sub> values of purchased nitrate salts and ureas were nearer to the known values when analyzed using thermal decomposition than using combustion.</p> </sec> <sec id="rcm7229-sec-0004" sec-type="section"> <title>Conclusions</title> <p>The thermal decomposition method addresses insufficient recovery of nitrogen during elemental analysis in a variety of organic and inorganic materials. Its implementation requires relatively few changes to the elemental analyzer. Using TDM, it is possible to directly calibrate certain organic materials to international nitrate isotope reference materials without off‐line preparation. Copyright © 2015 John Wiley & Sons, Ltd.</p> </sec> </abstract>