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Min, Deullae,Lee, Jin Bok,Lee, Christopher,Lee, Dong Soo,Kim, Jin Seog Korean Chemical Society 2014 Bulletin of the Korean Chemical Society Vol.35 No.8
Absolute isotope ratio is a critical constituent in determination of atomic weight. To measure the absolute isotope ratio using a mass spectrometer, mass discrimination factor, $f_{MD}$, is needed to convert measured isotope ratio to real isotope ratio of gas molecules. If the $f_{MD}$ could be predicted, absolute isotope ratio of a chemical species would be measureable in absence of its enriched isotope pure materials or isotope references. This work employed gravimetrically prepared isotope mixtures of argon (Ar) to obtain $f_{MD}$ at m/z of 40 in the magnetic sector type gas mass spectrometer (gas/MS). Besides, we compare the nitrogen isotope ratio of nitrogen trifluoride ($NF_3$) with that of nitrogen molecule ($N_2$) decomposed from the same $NF_3$ thermally in order to identify the difference of $f_{MD}$ values in extensive m/z region from 28 to 71. Our result shows that $f_{MD}$ at m/z 40 was $-0.044%{\pm}0.017%$ (k = 1) from measurement of Ar artificial isotope mixtures. The $f_{MD}$ difference in the range of m/z from 28 to 71 is observed $-0.12%{\pm}0.14%$ from $NF_3$ and $N_2$. From combination of this work and reported $f_{MD}$ values by another team, IRMM, if $f_{MD}$ of $-0.16%{\pm}0.14%$ is applied to isotope ratio measurement from $N_2$ to $SF_6$, we can determine absolute isotope ratio within relative uncertainty of 0.2 %.
Deullae Min,Jin Bok Lee,Christopher Lee,이동수,JIN SEOG KIM 대한화학회 2014 Bulletin of the Korean Chemical Society Vol.35 No.8
Absolute isotope ratio is a critical constituent in determination of atomic weight. To measure the absolute isotope ratio using a mass spectrometer, mass discrimination factor, fMD, is needed to convert measured isotope ratio to real isotope ratio of gas molecules. If the fMD could be predicted, absolute isotope ratio of a chemical species would be measureable in absence of its enriched isotope pure materials or isotope references. This work employed gravimetrically prepared isotope mixtures of argon (Ar) to obtain fMD at m/z of 40 in the magnetic sector type gas mass spectrometer (gas/MS). Besides, we compare the nitrogen isotope ratio of nitrogen trifluoride (NF3) with that of nitrogen molecule (N2) decomposed from the same NF3 thermally in order to identify the difference of fMD values in extensive m/z region from 28 to 71. Our result shows that fMD at m/z 40 was −0.044 % ± 0.017 % (k = 1) from measurement of Ar artificial isotope mixtures. The fMD difference in the range of m/z from 28 to 71 is observed −0.12 % ± 0.14 % from NF3 and N2. From combination of this work and reported fMD values by another team, IRMM, if fMD of −0.16 % ± 0.14 % is applied to isotope ratio measurement from N2 to SF6, we can determine absolute isotope ratio within relative uncertainty of 0.2 %.
Isotopic signatures of N2O produced by ammonia-oxidizing archaea from soils.
Jung, Man-Young,Well, Reinhard,Min, Deullae,Giesemann, Anette,Park, Soo-Je,Kim, Jong-Geol,Kim, So-Jeong,Rhee, Sung-Keun Nature Publishing Group 2014 The ISME journal Vol.8 No.5
<P>N2O gas is involved in global warming and ozone depletion. The major sources of N2O are soil microbial processes. Anthropogenic inputs into the nitrogen cycle have exacerbated these microbial processes, including nitrification. Ammonia-oxidizing archaea (AOA) are major members of the pool of soil ammonia-oxidizing microorganisms. This study investigated the isotopic signatures of N2O produced by soil AOA and associated N2O production processes. All five AOA strains (I.1a, I.1a-associated and I.1b clades of Thaumarchaeota) from soil produced N2O and their yields were comparable to those of ammonia-oxidizing bacteria (AOB). The levels of site preference (SP), δ(15)N(bulk) and δ(18)O -N2O of soil AOA strains were 13-30%, -13 to -35% and 22-36%, respectively, and strains MY1-3 and other soil AOA strains had distinct isotopic signatures. A (15)N-NH4(+)-labeling experiment indicated that N2O originated from two different production pathways (that is, ammonia oxidation and nitrifier denitrification), which suggests that the isotopic signatures of N2O from AOA may be attributable to the relative contributions of these two processes. The highest N2O production yield and lowest site preference of acidophilic strain CS may be related to enhanced nitrifier denitrification for detoxifying nitrite. Previously, it was not possible to detect N2O from soil AOA because of similarities between its isotopic signatures and those from AOB. Given the predominance of AOA over AOB in most soils, a significant proportion of the total N2O emissions from soil nitrification may be attributable to AOA.</P>