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Improved accuracy and precision in δ 15 N AIR measurements of explosives, urea, and inorganic nitrates by elemental analyzer/isotope ratio mass spectrometry using thermal decomposition
Author(s) -
Lott Michael J.,
Howa John D.,
Chesson Lesley A.,
Ehleringer James R.
Publication year - 2015
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.7229
Subject(s) - chemistry , thermal decomposition , nitrogen , decomposition , ammonium nitrate , combustion , elemental analysis , mass spectrometry , ammonium , analytical chemistry (journal) , nitrate , inorganic chemistry , ammonia , isotope ratio mass spectrometry , environmental chemistry , organic chemistry , chromatography
Rationale Elemental analyzer systems generate N 2 and CO 2 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 2 – for the analysis of these materials. Methods 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 2 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 2 . Results The δ 13 C VPDB 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, 15 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 δ 15 N AIR values of purchased nitrate salts and ureas were nearer to the known values when analyzed using thermal decomposition than using combustion. Conclusions 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.