Detailed Analytical Capabilities
Equipment
Micromass Optima continuous flow mass
spectrometer with electromagnet and universal triple collectors; capable
of analyzing CO2, O2, N2, CO, N2O,
and SO2. Peripherals include: Carlo Erba
C-N-S elemental analyzer preparation system, diluter, 3-gas reference
box, and separate small-sample and large-sample multi-tray carousels for
solids and dense liquids, for analysis for C, N, and S isotopes; a Eurovector high temperature pyrolysis
unit for the analysis of organics, inorganics
(esp. nitrates and phosphates), and waters for H and O (usually used for
solid samples); and an HP 5890 GC-combustion system for C-N isotopes of
volatiles and gases; a Tekmar 16-port purge and
trap mounted on the GC. All the Micromass
peripherals are mounted on wheels so that they can be used on any of the
three mass specs.
Micromass IsoPrime
continuous flow mass spectrometer (#1) with electromagnet, electrostatic
sector, universal triple collectors, H collectors, Cl
collectors -- capable of analyzing CO2, O2, N2,
CO, N2O, SO2, H2, and MeCl isotopes. Peripherals include: the “AutoScott #1” a custom modified MultiFlow (Gilson-type) automated headspace-gas
analyzer, used for analysis of N2O samples prepared using the Sigman-Casciotti microbial denitrifiers method for
nitrate N and O isotopes, but also useful for H2-H2O
and CO2 - H2O equilibrations (by CF), and analysis
of DIC.
Micromass IsoPrime
dual inlet/continuous flow mass spectrometer (#2) with electromagnet,
electrostatic sector, universal triple collectors, H, Cl,
and Br collectors -- capable of analyzing CO2, O2,
N2, CO, N2O, SO2, H2, MeCl, and MeBr isotopes.
Peripherals include: automatic dual inlet coldfinger,
diluter, 2-gas reference box, valve-top assembly (a 30-port multi-port
for samples in glass tubes), Eurovector high
temperature pyrolysis unit for the CF analysis
of waters for H (either manually or with the Eurovector
liquid autosampler); MultiPrep
used for H2-H2O and CO2 - H2O
equilibrations and analysis of carbonates (by dual inlet analysis); an HP
5890 GC-combustion system for C-N-Cl-Br
isotopes of volatiles and gases; and a TIC-TOC analyzer (from OI,
designed for analyzing DIC and DOC samples) provides automated analyses
of δ13C of DIC and DOC.
Micromass IsoPrime
continuous flow mass spectrometer (#3) with electromagnet, electrostatic
sector, universal triple collectors capable of analyzing CO2,
O2, N2, CO, N2O, SO2; plus
extra collectors for simultaneous analysis of SO and SO2, or N2
and N2/Ar ratios. Peripherals include: Carlo Erba C-N-S elemental analyzer preparation system,
diluter, 2-gas reference box, and multi-tray carousels for solids and
dense liquids, for analysis for C, N, and S isotopes; the “AutoScott #2” a custom modified MultiFlow (Gilson-type) automated headspace-gas
analyzer, used for analysis of N2O samples prepared using the Sigman-Casciotti microbial denitrifier method for
nitrate N and O isotopes, but also useful for H2-H2O
and CO2 - H2O equilibrations (by CF), and analysis
of DIC; and a high-temperature furnace for conversion of N2O
to N2 plus O2 for measurement of δ17O.
Los Gatos Research “laser spec” for analysis of waters for
O and H isotopes (Los Gatos Research DLT-100 Liquid-Water Isotope
Analyzer). This instrument uses
near infrared absorption spectroscopy to determine the isotopic
composition of water samples. 2mL
aliquots of sample are loaded into 2mL glass vials with split-cap septa
and placed into the auto-sampler.
For each sample, 4 to 6 sequential 1.2 µL aliquots of sample are
injected into the instrument through the auto-sampler. Two internal water
standards are measured after every 5th sample. The results for the first aliquot are
discarded, the remaining aliquots examined for additional outliers, and
the acceptable are averaged and corrected for per mil scale
linearity. Precision of this
method based on repeated standard measurements is about 0.2 ‰ for O
and 0.5‰ for H isotopes.
Vacuum lines: carbonate/water extraction line, zinc method preparation
line, "Craig-type" CO2-CH4 line,
reference gas-standard preparation line w/ 400 split capacity.
Tritium lab: 4 liquid scintillation counters for tritium and 35S,
3H extraction systems (distillation and electrolysis).
Capabilities
Waters for 2H and 18O: Standard sample
size for water equilibrations is 2.0 ml per analysis (for both H and O
isotopes); 0.1 ml is the minimum size for automated equilibrator
preparation. We have 3 different types of equilibrators on 3 different
mass specs, a pyrolysis unit (with autosampler) on the dual inlet IsoPrime,
and a laser spec. The pyrolysis unit requires only a few ml per analysis. The new laser
spec requires only a few ml per
analysis. Water is extracted from
soils and plants by distillation with toluene; recommended sample size is
1-5 ml water per analysis. Analytical precision is 0.05 to 0.1 ‰
for 18O, and 0.3 to 2.0 ‰ for 2H, depending
on method and sample matrix.
Waters for 3H: Tritium concentrations are measured
on raw unfiltered (RU) waters collected and stored in either glass or
high density polyethylene bottles. The size of the bottle depends on the
level of precision desired.
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Two sigma
detection limit
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+/- 8 TU
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+/- 1.2 TU
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+/- 0.6 TU
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+/- 0.3 TU
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Suggested
volume
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25 ml
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500 ml
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500 ml
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1000 ml
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Electrolyzed
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No
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Yes
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Yes
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Yes
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13C of DIC:
Most samples these days are analyzed using the automated TIC/TOC. But there are other methods than can be
used. For example, we can use the Multiflow or MultiPrep autosamplers to do headspace analysis of dissolved CO2.
This requires only a few m moles
of C and produces precisions better than 0.1 ‰. Alternatively, samples can be
precipitated with SrCl2 in a NH4OH solution,
filtered, rinsed, acidified, and the purified CO2 analyzed;
recommended sample size is >50 m
moles of C (200 uM DIC concentrations are
sometimes required to get adequate precipitation of SrCO3 with
this method). Alternatively, organic-free precipitates can be combusted
on the elemental analyzer connected to the Optima mass spectrometer, or
organic-bearing precipitates can be baked to remove organics and then
combusted. These combustion methods only require a few umoles of C. Analytical precision: 0.1 to 0.2
‰.
13C/18O of carbonates: Samples are usually analyzed using the MultiFlow or MultiPrep autosamplers, where sample sizes are usually on the
order of a mmole. Manual
single-sample preparation system; samples are acidified, purified, and
the resultant CO2 samples loaded on the automated inlet
manifold and analyzed. Recommended sample size >50 mmoles of C. Analytical precision: 0.05
to 0.1 ‰.
13C/15N of solids and dense liquids: Samples are loaded into tin boats
100-200 samples in a batch, combusted, and analyzed for bulk elemental
and isotopic composition on the elemental analyzer connected (usually) to
the Optima. Recommended sample size is 2-10 m moles of N if both C and N isotopes are to be measured
(this is about 1-2 mg for typical organic samples). Actual minimum sample
size is about 0.01 m moles.
Maximum sample weight is about 300 mg. Both C and N isotopes can be
determined on the same sample if the %C and the C:N
ratio are known (so that the correct sample size is weighed and the
diluter adjusted correctly). Analytical precision: 0.1 to 0.2 ‰.
15N/18O of nitrate: We are no longer using the silver
nitrate method (published in Silva et al., 2000). Currently all samples are analyzed
using the Sigman-Casciotti microbial
denitrifier method to convert nitrate to N2O, which is then
analyzed for 18O and 15N simultaneously. This
method requires only about 50 nanomoles of N
per aliquot, has no interference with other N-bearing substances, and can
be used on saline samples. Our analytical precision is about 0.5 ‰
for N and 1.0 ‰ for O. We
have a prototype system working for δ17O of nitrate.
15N of ammonium: Samples are analyzed using the
micro-diffusion method. Recommended sample size is 50 mmoles, with allows for several
analyses at 2 mmoles per aliquot.
Our analytical precision is about
0.5 ‰.
18O of phosphate: Aqueous samples are collected on
anion exchange resins in the field, and processed similarly to nitrate.
Our method can handle low phosphate, high sulfate, and high DOC
concentrations, and requires about 50 m moles
of PO4 per analysis using sealed tiube
combustions and about 5 m moles
of PO4 for pyrolysis analyses. We
get precisions of about 0.2 ‰ for solid samples and 0.2 to 0.5
‰ for aqueous samples.
18O of organics and inorganics:
Can be analyzed on the automated pyrolysis
system, for samples sizes on the order of a few micromoles of O per
sample.
18O of O2 gas: Samples are
collected in evacuated bottles and are purified and analyzed on an EA
using the Wassenaar method.
13C, 15N, 18O of gases:
Currently, such samples are injected manually into either the elemental
analyzer or GC combustion system, and analyzed for one or more
constituents at a time. Future plans: analyze such samples (and dissolved
gases) using the Microgas automated headspace
system.
13C of hydrocarbon and other gas mixtures: Volatile
materials are injected manually into the GC combustion system where
constituent peaks are separated using the appropriate GC column,
combusted to CO2, purified online, and then each peak is
analyzed for 13C. Minimum sample size is in the range of 1-10 nanomoles per peak, with precisions of 0.1 to 0.3
‰.
15N of volatile organics and gas mixtures: Materials
are handled similarly to above, but the samples are instead combusted to
N2, reduced and purified, and then constituent peaks through
the GC are analyzed for 15N. Minimum sample size is in the
range of 1-10 nanomoles per peak, and
precisions are 0.1 to 0.5 ‰.
34S of solids (organics and inorganics):
Samples are loaded into tin boats 100-200 samples in a batch, combusted,
and analyzed for bulk elemental and isotopic composition on the elemental
analyzer connected to the IsoPrime or Optima.
Recommended sample size is 2-10 m
moles. If needed, C-N-S isotopes can all be measured on the same sample,
but it is much easier to do separate S and C+N determinations. Analytical
precision: <0.2 ‰.
35S of sulfate: Samples are collected on ion
exchange resins in the field. Approximately 20 liters of sample water is
passed thru the resin. The samples are returned to the laboratory for
elution, preparation, and counting in a liquid scintillation counter. For
best analytical results, sulfate concentrations should be less than 0.002 moles/L. For very low concentrations
(0.0001 mole/L and less), a sodium sulfate carrier is provided by the
laboratory.
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