Transcript 18O Analysis of Organic Compounds combining an Elementar PYRO, Interfaced with a  Conflo II - Thermo Delta V -                           Mass Spectrometer

18O analysis of organic compounds
combining an Elementar PYRO
interfaced with a Conflo II and
Thermo Delta V mass spec.
By Paul D. Brooks and Todd E. Dawson.
Univ. of California, Berkeley.
Disclaimer
• The product names used in this presentation are for
information only and do not constitute a promotion
or endorsement by the University of California,
university affiliates or employees.
Acknowledgements
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The authors would like to thank:
Steve Silva, USGS Menlo Park, Ca.
Scott Hughes, Elementar Americas Inc.
Robin Sutka, formally of Elementar Americas Inc.
Mike Seed, Isoprime Ltd
Joy Mathews, UC Davis.
Paul Middlestead, Univ. of Ottawa.
Everyone who has replied to questions on
Isogeochem and/or has attended ASITA or earlier
CF-IRMS conferences.
Why is high precision, reliable 18O needed?
Why is it an advantage to be able to analyze
samples as small as 0.1 mg O?
California coastal redwoods in summer
fog.
Known:
1) California redwoods take up fog water directly in through
their leaves in summer.
2) Fog and soil water have different isotope ratios.
3) The amount of fog in summers is affected by El Niño events
Redwood samples from John Roden, analysis mine.
Arcata Redwood
1998
1999
2000
2001
2002
18
d Ocellulose (‰)
29
28
27
26
Relative distance along core (mm)
2003
NA 1500
VENT TO HOOD
12
VENT
13
1
Main valve
9
To MS
Conflo II
NC
2
8
3
7
Ni wool
VENT
4
6
5
NiC catalyst
1130°C
#1
NO
C
NC
G.C. column
C
NO
14
11
10
He
Sampler
Acid trap
He
Ni wool
#2
He
doped
with chloropentane
Delta V output, old system
IAEA V9 cotton cellulose QC, old system 2005- Jan 2013
0.3 to 0.8 mg O
31.00
delta 18O SMOW
30.00
29.00
28.00
27.00
Average = 28.64
Std Dev = 0.28
26.00
25.00
14-Jan-2004 28-May-2005 10-Oct-2006
22-Feb-2008
6-Jul-2009
analysis date
18-Nov-2010
1-Apr-2012
14-Aug-2013
Problems with the old system
• Custom built system complicated and difficult to
use.
• Results deteriorated below 0.3 mg O.
• Required a large number of standards for drift
correction and normalization.
• Long term QC deteriorated over several years.
• The pyrolysis column had to be re-packed every
300 capsules (198 samples).
• After packing the pyrolysis tube had to be left at
temperature overnight to lower mass 30
background.
Old system linearity
delta value
linearity with size correction
28.000
27.500
27.000
26.500
26.000
25.500
25.000
24.500
0.200
reported
fit
corr
0.400
mg O
0.600
actual
Use a Low Emission Current for CO to
Achieve Better Linearity
75 to 90 mA
Best Filament Current Setting
3
18O "Linear" Results at Different Emmision Currents
2
d 18O (2nd sample = 0)
55 mA
1
75 mA
0
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
90 mA
110 mA
-1
126 mA
-2
90 mA - 2
-3
-4
• Used “Linear Tuning”
method
– Start at extraction and tune
your way out
• Never achieved acceptable
linearity below 5V
• Instrument still must meet
the stability specification
Mass 28 Amplitude (mV)
From Todd Brown, Monsanto, M [AG/1005]" <[email protected]>
Replacing EA
• Old EA was replaced with
Elementar PYRO Cube.
• The existing Thermo Delta V and
Conflo II were used to save on
costs.
PYRO/Delta V O analysis setup
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PYRO was installed with factory specifications for O analysis:
Standard pyrolysis tube packing for O analysis.
Pyrolysis temperature of 1450°C.
Carrier gas flow rate of 125 mL/min.
Trap CO at 40°C, desorb at 100°C.
Carousel temperature set to 60°C to mitigate sample moisture adsorption.
PYRO is method is started by contact closure from Delta V.
• Non-factory spec:
• Using purge flow round glassy carbon tube of 230 mL/min. Using He at
present but plumbing set up to use Ar if necessary.
• Data from Delta V and PYRO must be combined from two different files after
analysis.
• Delta V method drives analysis, so PYRO method must be slightly shorter than
Detla V method.
PYRO ash (molten silver) finger.
PYRO set up in lab.
PYRO TCD output
Delta V output, PYRO.
Standardization Protocol
• Drift is measured with 0.4-0.5 mg O (09 to 1.1 mg material)
sigma cellulose standard at 26.4 δ 18O every 12 samples.
• Linearity is adjusted with 0.1-0.7 mg O variable weight
sigma standards placed evenly throughout the run.
• Normalization is calculated with 5 IAEA-C3 set to 32.2 δ 18O
spaced evenly throughout the run
• QC is 5 IAEA-V9 cotton cellulose standards spaced evenly
throughout the run.
• IAEA-C3 and V9 are in the same size range as the variable
weight sigma standards.
• This was the standardization protocol for the old system
and it may be possible to use less calibration standards.
• Out of 99 total capsules per run 66 are unknown samples.
Old system linearity
delta value
linearity with size correction
28.000
27.500
27.000
26.500
26.000
25.500
25.000
24.500
0.200
reported
fit
corr
0.400
mg O
0.600
actual
Non-linearity with size.
delta value
p2p linearity with size correction
28.000
27.500
27.000
26.500
26.000
25.500
25.000
24.500
0.000
reported
fit
corr
0.200
0.400
mg O
0.600
0.800
actual
Considerations/Observations
• The Conflo II maximum reference gas peak height is 9000 mv
when the sample peaks can range up to 50,000 mv. This limits
the ability to tune the Delta V for linearity. (Buy a Conflo IV?)
• The standards are in a narrow range from 26.4 to 32.2 δ 18O.
This is acceptable for 90% of samples we have analyzed. We are
experimenting with some coastal redwood leaf standards at 22 δ
18O and some Sierra redwood at 41-45 δ 18O.
• There is no memory (carryover) effect.
• The 60°C carousel appears to mitigate any moisture adsorption.
The results have been excellent even with standards left in the
lab air overnight compared to standards kept in a desiccator.
Throughput
• The system analyzes 99 capsules in 24.5 hours.
• At present this is 66 unknowns but this may be
increased as less standards may be required.
• The ash finger is removed and silver plug knocked out
with the system cool on Monday morning.
• The PYRO takes about 1 hour to heat to 1450°C, then
is ready for analysis.
• 495 silver capsules are analyzed during the week
before the ash finger has to be removed.
• After over 1,700 capsules the acid/water trap does not
need replacing.
QC – to present
IAEA V9 cotton cellulose QC, old system 2005- Jan 2013
PYRO Feb-May 2013 0.3 to 0.8 mg O
(PYRO 0.1 to 0.8 mg O stdev=0.21)
delta 18O SMOW
31.00
30.00
29.00
28.00
27.00
Old System Average = 28.64
Std Dev = 0.28
26.00
25.00
1-Aug-2004
14-Dec-2005
28-Apr-2007
9-Sep-2008
22-Jan-2010
analysis date
6-Jun-2011
PYRO
Avg= 28.69
Stdev=0.16
18-Oct-2012
2-Mar-2014
Conclusions
• The PYRO/Conflo II/Delta V combination works
well.
• A sample range of 0.1 to 0.8 mg O is quite usable
with slight non-linearity at the lower weight
range.
• Maintenance has been minimal.
• Throughput is at least 330 unknowns per week.
• QC with a standard deviation of 0.16 δ18O is a
significant improvement on the old system.