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Carbon and nitrogen isotope analysis of
solids by EA-IRMS |
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Solid
materials including sediments, soil, freeze-dried extracts and biological
samples (plant, fish, invertebrate tissue, feather, blood) are analysed using
a Sercon 20-22 IRMS with integrated elemental analyzer. C and N isotope analysis are commonly performed
simultaneously. Limit
of quantification: 0.03mg N, 0.1mg C Precision
for elemental analysis: 0.5µg for both C and N Precision
for stable isotope analysis: ±0.2‰ for δ15N; ±0.1‰ for δ13C |
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Carbon dioxide and dinitrogen gas isotope
analysis |
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Both CO2
and N2 (in air or headspace samples) at natural abundance level
are analysed on a Sercon 20-22 IRMS with integrated
cryoprep trace gas module. We also accept samples
with 15N-labelled N2. Precision
of the instrument: ±0.3‰ for both δ15N-N2 and
δ13C-CO2 |
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Nitrate
and nitrite isotope analysis with the azide method |
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To analyse N and O
isotopes of dissolved NOx and NO3- in water samples,
NOx/NO3- is converted to NO2-
using cadmium then to N2O using sodium azide.
The resultant N2O is measured using a Sercon
20-22 IRMS interfaced with a cryoprep trace gas
module. A reference N2O peak is used to calculate provisional isotope
ratios of the sample N2O peak. These provisional values are used
to calculate the final δ15N and δ18O of NO3-
using calibration standards (USGS32, USGS34 and USGS35) which are supplied by
NIST (National Institute of Standards and Technology, Gaithersburg, MD). Limit of
quantification: 0.1mg/L NO3-N Precision of the
instrument: ±0.5‰ for δ15N; ±0.3‰ for δ18O Reference: McIlvin and Altabet (2005) http://pubs.acs.org/doi/abs/10.1021/ac050528s |
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Ammonium
isotope analysis with the ammonium diffusion and hypobromide
methods |
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We perform N isotope
analysis for NH4+ at natural abundance level and for
labelled 15N-NH4+. For natural abundance
level, NH4+ is converted to NO2-
using hypobromide then to N2O using
sodium azide. For labelled isotope analysis, NH4+
is converted to N2 using hypobromide.
Both N2O and N2 are analysed on the IRMS interfaced
with a cryprep module. Limit of
quantification: 0.1mg/L NH4-N Reference: Zhang et al. (2007) http://www.ncbi.nlm.nih.gov/pubmed/17567102 |