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

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

The old system

CO2

CO2

N2 (L)

4 Panetta (2008), Analytical Chemistry

6 x 150μL injections 45 minutes

The new system

CO2

CO2

Electric Cue

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

IR detector

To IRMS Sam

ple

680oC

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

O2 +CO2 from DOC

He gas

IRMS

O2 + CO2 He gas Not in use

13

CO2 Trapping system

CO2 trapped

O2 +CO2 from DOC

He gas

IRMS

O2 + CO2 He gas Not in use

Clean O2

14

CO2 Trapping system

CO2 trapped

O2 +CO2 from DOC

He gas

IRMS

O2 + CO2 He gas Not in use

Removed O2

15

CO2 Trapping system

CO2 trapped

O2 +CO2 from DOC

He gas

IRMS

O2 + CO2 He gas Not in use

Trap is heated to 250oC

16

It works!!

17

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

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

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

-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

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 ‰

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‰

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‰

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 (‰)

26

Salinity (psu)

Acknowledgements

27

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)