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This presentation discusses the analysis of organic compounds using an Elemental PYRO interfaced with a Conflo II and Thermo Delta V mass spec. It explores the need for high precision and reliable 18O analysis and the advantages of analyzing samples as small as 0.1 mg O. The presentation also includes information on the California coastal redwoods and the analysis setup using the PYRO Cube.
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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. • RobinSutka, formally of ElementarAmericas 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?
Known: • California redwoods take up fog water directly in through their leaves in summer. • Fog and soil water have different isotope ratios. • The amount of fog in summers is affected by El Niño events
VENT TO HOOD Sampler 12 13 C VENT NO 14 11 #2 10 1 N C He Main valve 9 2 He doped with chloro-pentane 8 3 Ni wool VENT 7 4 NiC catalyst 1130°C To MS 5 6 Conflo II #1 NO C Ni wool He N C G.C. column Acid trap
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.
Use a Low Emission Current for CO to Achieve Better Linearity 75 to 90 mA Best 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 From Todd Brown, Monsanto, M [AG/1005]" <todd.m.brown@monsanto.com>
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.
Standardization Protocol • Drift is measured with 0.4-0.5 mg O (09 to 1.1 mg material) sigma cellulose standard at 26.4 δ18O 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 δ18O 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.
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 δ18O. This is acceptable for 90% of samples we have analyzed. We are experimenting with some coastal redwood leaf standards at 22 δ18O and some Sierra redwood at 41-45 δ18O. • 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.
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.
