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Measuring 13 C of dissolved organic carbon in freshwater and - - PowerPoint PPT Presentation

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Measuring 13 C of dissolved organic carbon in freshwater and seawater ASITA conference 2014 Karine Lalonde , Paul Middlestead, Yves Glinas Concordia University, University of Ottawa 1 The seawater DOC challenge Large active pool of

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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

2

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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)

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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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SLIDE 8

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 Sample 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?

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 2 4 6 8 10 12

Standard deviation (‰) 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
  • 4

0.1 0.2 0.3 0.4 0.5

raw δ13C (‰) 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
  • 4

20 25 30

δ13C (‰) System pressure (PSI)

KHP/algae mix = -9.0‰ IAEA sucrose = -10.5‰

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Injection volume and combustion

  • 12
  • 11
  • 10
  • 9
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  • 6
  • 5

1500 1200 750 500

δ13C (‰) 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)