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)

d18 O

cellu

lose

(‰)

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

delta

18O

SM

OW

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 0.70023.00024.00025.00026.00027.00028.000

linearity with size correction

reported

fit

corr

actual

mg O

delta

val

ue

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]" <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.

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 0.70023.00024.00025.00026.00027.00028.000

linearity with size correction

reported

fit

corr

actual

mg O

delta

val

ue

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

delta

val

ue

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

delta

18O

SM

OW

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.