measuring δ13c of dissolved organic · 2014. 8. 1. · the evolution of seawater δ 13 c doc 1968...
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Measuring δ13C of dissolved organic carbon in freshwater and seawater
ASITA conference 2014
Karine Lalonde, Paul Middlestead, Yves Gélinas Concordia University, University of Ottawa
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The seawater DOC challenge
• Large active pool of reduced carbon – (700 x 1015 g OC)
• For 1 L of seawater – 35g of salts – As low as 0.5mg OC
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The evolution of seawater δ13CDOC
1968
1992
[Fry 1992] lyophilization V = 25 mL 3 hours Not automated
2003-2008
[Beaupré 2007] UV oxidation V = 30-650mL 4-5 hours Not automated
[Lang 2007], [Panetta 2008] HTC-DOC V = 5-10 mL 45 min Not automated
[St-Jean 2003], [Osburn 2007] Wet oxidation V = 10-25mL 20 min Not automated
NOW
HTC-DOC V = 5-10 mL 20 min automated
[Williams 1968] UV oxidation V = 1.8 L 6 hours Not automated
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The old system
CO2
CO2
N2 (L)
4 Panetta (2008), Analytical Chemistry
6 x 150μL injections 45 minutes
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The new system
CO2
CO2
Electric Cue
Electric Cue
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CO2 trapping system
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Special thanks to
Paul Middlestead G. G. HATCH Laboratory
Graham Hughes Graden Instruments
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Humm
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Benefits of Automation
• Fewer mistakes • Longer sequences
– Higher throughput – More controls – More replicates – Better standard deviations – Better idea of system limitations/capabilities
• Better relationship with your grad students./support staff
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Dissolved organic carbon (DOC) analyzer: Water
and salt traps
IR detector
To IRMS Sam
ple
680oC
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CO2 peak problems
• Peak from the DOC analyzer:
1. Tails due to differing combustion efficiencies
2. About 3 minutes wide 3. CO2 peak is in Oxygen
gas
• Peak requirements for IRMS
1. Peak should be as narrow and as intense as possible
2. Peak must be in He gas
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CO2 Trapping system
CO2 from DOC
Heat to 250oC
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CO2 Trapping system
O2 +CO2 from DOC
He gas
IRMS
O2 + CO2 He gas Not in use
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CO2 Trapping system
CO2 trapped
O2 +CO2 from DOC
He gas
IRMS
O2 + CO2 He gas Not in use
Clean O2
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CO2 Trapping system
CO2 trapped
O2 +CO2 from DOC
He gas
IRMS
O2 + CO2 He gas Not in use
Removed O2
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CO2 Trapping system
CO2 trapped
O2 +CO2 from DOC
He gas
IRMS
O2 + CO2 He gas Not in use
Trap is heated to 250oC
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It works!!
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No matrix effects Little to no carry over from the combustion column
Sample true δ13C values
(‰)
DOC –IRMS δ13C PAUL (‰)
DOC –IRMS δ13C ConU (‰)
Sucrose (In-house) -11.77 -12.1 ± (NA) -11.6 ± (0.2)
KHP* -28.16 -27.8 ± (NA) -28.1 ± (0.2)
β-Alanine -26.18 -25.3 ± (NA) -26.1 ± (0.2)
Suwanee river fulvic acid -27.60 -27.4 ± (NA) -27.8 ± (0.2)
Deep Florida Straight water ? -20.6 ± (0.3) -19.9 ± (0.5)
*KHP = potassium hydrogen phthalate
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How low can you go?
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0 2 4 6 8 10 12
Stan
dard
dev
iatio
n (‰
)
Concentration (ppm)
High blank contribution
Low blank contribution
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Where does the blank come from?
• The blank comes from the column packing
• δ13C of the blank is between -20 & -12‰
• Pretty constant intensity and signature over one sequence
• Variable over many sequences – Must be corrected before
running samples
CO2
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Accounting for the blank
-28
-24
-20
-16
-12
-8
-40 0.1 0.2 0.3 0.4 0.5
raw
δ13
C (‰
)
1/MH (nA-1)
Sucrose (-10.47‰)
β-Alanine (-26.18‰)
KHP(-28.16‰)
δb = (Slope / ηb) + δbc
IRMS blank intensity
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Testing combustion efficiency
KHP, δ13C = -28.2‰
Enriched algae δ13C = +11.6‰
sucrose, δ13C = -10.5‰
Incomplete combustion results in δ13C shifts 100% combustion δ13C = -9 ‰ 5% of KHP is not combusted = -7.6 ‰
Incomplete combustion results in no δ13C shifts δ13C always = -10.5 ‰
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DOC system pressure and combustion
-12
-11
-10
-9
-8
-7
-6
-5
-420 25 30
δ13 C
(‰)
System pressure (PSI)
KHP/algae mix = -9.0‰
IAEA sucrose = -10.5‰
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Injection volume and combustion
-12
-11
-10
-9
-8
-7
-6
-51500 1200 750 500
δ13 C
(‰
)
Injection Volume (μL)
KHP/algae mix = -9.0‰
IAEA sucrose = -10.5‰
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Seawater.. Is it possible?
• Matrix does not affect combustion efficiency • Low concentration of seawater DOC are
problematic – Lowest possible standard deviations are ± 0.5‰ at 0.5
ppm • See Andrew Barber’s poster tonight!
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δ13C signature in the SLE (‰)
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Salinity (psu)
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Acknowledgements
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Yves Gélinas
Alfonso Mucci
Committee members
• Xavier Ottenwaelder
• Cameron Skinner
Lab members
• Andrew Barber
• Mina Ibrahim
• Alexandre Ouellet
• Anja Moritz
• Rob Panetta
Technical Help and Others
• Anssi Vähätalo
• Paul Middlestead (University of Ottawa)
• Graham Hughes (OI technologies)
• Alain Tessier (CBAMS)
• Richard and Aldo (Machine shop)
• Dan (Electronics Shop)