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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
• 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
26
27
28
29
Relative distance along core (mm)
d18O
ce
llulo
se (
‰)
20031998 1999 2000 2001 2002
NA 1500
1
3
2
45
76
9
8
10
1112 13
14VENT
VENT TO HOOD
To MS
G.C. column
He
Sampler
N C
CNO
He
Acid trap
Conflo II
Ni wool
Ni wool
NiC catalyst 1130°C
#2
#1
HeCNO
N C
VENT
Main valve doped with chloro-
pentane
Delta V output, old system
14-Jan-2004 28-May-2005 10-Oct-2006 22-Feb-2008 6-Jul-2009 18-Nov-2010 1-Apr-2012 14-Aug-201325.00
26.00
27.00
28.00
29.00
30.00
31.00
IAEA V9 cotton cellulose QC, old system 2005- Jan 20130.3 to 0.8 mg O
analysis date
de
lta
18
O S
MO
W
Average = 28.64Std Dev = 0.28
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
0.200 0.300 0.400 0.500 0.600 0.70023.000
24.000
25.000
26.000
27.000
28.000
linearity with size correction
reported
fit
corr
actual
mg O
del
ta v
alu
e
Use a Low Emission Current for CO to Achieve Better Linearity
75 to 90 mABest Filament Current Setting
• 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
-4
-3
-2
-1
0
1
2
3
0 2000 4000 6000 8000 10000 12000 14000 16000 18000
d18O
(2nd
sam
ple
= 0)
Mass 28 Amplitude (mV)
18O "Linear" Results at Different Emmision Currents
55 mA
75 mA
90 mA
110 mA
126 mA
90 mA - 2
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• 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
0.200 0.300 0.400 0.500 0.600 0.70023.000
24.000
25.000
26.000
27.000
28.000
linearity with size correction
reported
fit
corr
actual
mg O
del
ta v
alu
e
Non-linearity with size.
0.100 0.200 0.300 0.400 0.500 0.600 0.70024.500
25.500
26.500
27.500
p2p linearity with size correction
reported
fit
corr
actual
mg O
del
ta v
alu
e
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
1-Aug-2004 14-Dec-2005 28-Apr-2007 9-Sep-2008 22-Jan-2010 6-Jun-2011 18-Oct-2012 2-Mar-201425.00
26.00
27.00
28.00
29.00
30.00
31.00
IAEA V9 cotton cellulose QC, old system 2005- Jan 2013PYRO Feb-May 2013 0.3 to 0.8 mg O
(PYRO 0.1 to 0.8 mg O stdev=0.21)
analysis date
de
lta
18
O S
MO
W
Old System Average = 28.64 Std Dev = 0.28
PYROAvg= 28.69Stdev=0.16
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.