Automation of 13 C/ 12 C ratio measurement for seawater DOC

Automation of 13 C/ 12 C ratio measurement for seawater DOC

Measuring δ13C of dissolved organic
carbon in freshwater and seawater
ASITA conference 2014
Karine Lalonde, Paul Middlestead, Yves Gélinas
Concordia University, University of Ottawa
1
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
2
The evolution of seawater δ13CDOC
[St-Jean 2003],
[Osburn 2007]
Wet oxidation
[Williams 1968]
UV oxidation
V = 1.8 L
6 hours
Not automated
1968
[Beaupré 2007]
V = 10-25mL
UV oxidation
20 min
V = 30-650mL
Not automated
4-5 hours
Not automated
1992
HTC-DOC
V = 5-10 mL
2003-2008
20 min
automated
[Fry 1992]
lyophilization
V = 25 mL
3 hours
Not automated
[Lang 2007],
[Panetta 2008]
HTC-DOC
V = 5-10 mL
45 min
Not automated
NOW
The old system
CO2
N2 (L)
CO2
6 x 150μL injections
45 minutes
Panetta (2008), Analytical Chemistry
4
The new system
Electric Cue
CO2
CO2
Electric Cue
5
CO2 trapping system
6
Special thanks to
Paul Middlestead
G. G. HATCH Laboratory
Graham Hughes
Graden Instruments
Humm
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
Dissolved organic carbon (DOC) analyzer:
Water
and salt
traps
Sample
IR detector
680oC
To IRMS
10
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
11
CO2 Trapping system
CO2 from DOC
Heat to 250oC
12
CO2 Trapping system
He gas
IRMS
O2 +CO2
from DOC
O2 + CO2
He gas
Not in use
13
CO2 Trapping system
He gas
IRMS
CO2 trapped
Clean O2
O2 +CO2
from DOC
O2 + CO2
He gas
Not in use
14
CO2 Trapping system
He gas
IRMS
CO2 trapped
O2 +CO2
from DOC
Removed O2
O2 + CO2
He gas
Not in use
15
CO2 Trapping system
He gas
IRMS
CO2 trapped
Trap is heated to 250oC
O2 +CO2
from DOC
O2 + CO2
He gas
Not in use
16
It works!!
17
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
No matrix effects
Little to no carry over from the combustion column
How low can you go?
0.9
Standard deviation (‰)
0.8
High blank
contribution
0.7
0.6
0.5
Low blank
contribution
0.4
0.3
0.2
0.1
0
0
2
4
6
8
Concentration (ppm)
10
12
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
Accounting for the blank
1/MH (nA-1)
-4
0
0.1
0.2
0.3
0.4
0.5
raw δ13C (‰)
-8
-12
Sucrose (-10.47‰)
-16
-20
β-Alanine (-26.18‰)
KHP(-28.16‰)
-24
-28
δb = (Slope / ηb) + δbc
IRMS blank intensity
Testing combustion efficiency
sucrose, δ13C = -10.5‰
KHP, δ13C = -28.2‰
Enriched algae δ13C = +11.6‰
Incomplete combustion results in no
δ13C shifts
δ13C always = -10.5 ‰
Incomplete combustion results in δ13C shifts
100% combustion δ13C = -9 ‰
5% of KHP is not combusted = -7.6 ‰
DOC system pressure and combustion
System pressure (PSI)
20
25
30
-4
-5
δ13C (‰)
-6
-7
-8
-9
KHP/algae mix = -9.0‰
-10
-11
-12
IAEA sucrose = -10.5‰
Injection volume and combustion
Injection Volume (μL)
1500
1200
750
500
-5
-6
δ13C (‰)
-7
-8
-9
-10
-11
-12
KHP/algae mix = -9.0‰
IAEA sucrose = -10.5‰
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!
δ13C signature in the SLE (‰)
Salinity (psu)
26
Acknowledgements
Yves Gélinas
Technical Help and Others
Alfonso Mucci
• Anssi Vähätalo
Committee members
• Paul Middlestead (University of Ottawa)
• Xavier Ottenwaelder
• Graham Hughes (OI technologies)
• Cameron Skinner
• Alain Tessier (CBAMS)
Lab members
• Richard and Aldo (Machine shop)
• Andrew Barber
• Dan (Electronics Shop)
• Mina Ibrahim
• Alexandre Ouellet
• Anja Moritz
• Rob Panetta
27