STABLE ISOTOPE ANALYSIS TECHNIQUES
Analysis: Carbon-13 & Nitrogen-15 of bulk materials
Technique: EA-IRMS (Elemental Analysis - Isotope Ratio Mass Spectrometry)
For determination of carbon-13 and nitrogen-15 the bulk
material must first be converted to pure N2 and CO2 to
permit analysis by IRMS. In this technique, samples are placed in clean tin
capsules and loaded into an automatic sampler. They are then dropped into a combustion
furnace held at 1000 deg. C where they are combusted in the presence of an
excess of oxygen. The tin capsules flash combust causing the temperature in the
vicinity of the sample to rise to ca. 1700 deg. C. The
gaseous products of combustion are swept in a helium stream over a Cr2O3
combustion catalyst, CuO wires to oxidize hydrocarbons
and silver wool to remove sulfur and halides. The resultant gases (N2,
NOx, H2O, O2, and CO2)
are then swept through a reduction stage of pure copper wires held at 600 deg.
C. This removes any remaining oxygen and converts NOx
gases to N2. Water is removed by a magnesium perchlorate
trap, while removal of CO2 is available using a selectable Carbosorb™ trap.
Nitrogen and carbon dioxide are separated
by a packed column gas chromatograph held at an isothermal temperature. The
resultant chromatographic peaks sequentially enter the ion source of the IRMS
where they are ionised and accelerated. Gas species
of different mass are separated in a magnetic field and simultaneously measured
by a Faraday cup universal collector array. For N2, masses 28, 29
and 30 are monitored and for CO2, masses 44, 45 and 46.
Analysis: Sulphur-34 of bulk materials
Technique: EA-IRMS (Elemental Analysis - Isotope Ratio Mass Spectrometry)
For determination of sulphur-34 the bulk material must first
be converted to pure SO2 to permit analysis by IRMS. In this
technique, samples are placed in clean tin capsules and loaded into an
automatic sampler. They are then dropped into a combustion furnace held at 1080
deg. C where they are combusted in the presence of an excess of oxygen. The tin
capsules flash combust causing the temperature in the vicinity of the sample to
rise to ca. 1700 deg. C. The gaseous products of
combustion are then swept in a helium stream through tungstic
oxide and zirconium oxide combustion catalysts and then reduced over high purity copper wires.
Water is removed by a Nafion™
membrane, permeable to only water. Sulphur dioxide is separated by a packed
column gas chromatograph held at an isothermal temperature. The resultant SO2
chromatographic peak enters the ion source of the IRMS where it is ionised
and accelerated. Gas species of different mass are
separated in a magnetic field and simultaneously measured by a Faraday cup
universal collector array. For SO2, masses 64, 65 and 66 are
monitored.
Analysis: Deuterium and Oxygen-18 of bulk materials
Technique: EA-IRMS (Elemental Analysis - Isotope Ratio Mass Spectrometry)
For determination of deuterium and oxygen-18, the bulk
material must first be converted to pure H2 and CO to permit
analysis by IRMS. In this technique, samples are placed in clean silver
capsules and loaded into an automatic sampler. They are then dropped into a
high temperature furnace where they are converted to H2 and CO in
the presence of glassy carbon. Residual water is removed by a magnesium perchlorate
trap, while any traces of CO2 is removed by a Carbosorb™ trap. H2
and CO are separated by a packed column gas chromatograph held at an isothermal
temperature. The resultant chromatographic peak enters the ion source of the
IRMS where it is ionised and accelerated. Gas species
of different mass are separated in a magnetic field then simultaneously
measured on a Faraday cup universal collector array. For CO, masses 28, 29 and
30 are monitored, while for H2 masses 2 and 3 are monitored.
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