SLIDE 1 EA-irms of sub-micromolar C samples:
Concentration and δ13C of DOC in sediment pore water
ASITA Conference 2014: Advances in Stable Isotope Techniques and Applications University of California, Davis
Koushik Dutta
Department of Earth and Planetary Sciences Large Lakes Observatory,
Swenson College of Science and Engineering
SLIDE 2 Objectives
- Elemental Analyzers coupled with IRMS in their “standard configuration”
typically require samples with ~ 30 to 600 µg carbon for δ13C analysis. Performances of two commercial EA-irms systems were evaluated analyzing precise amounts of organic C standards in sub-micromolar range
- Evaluation of carbon backgrounds of tin and silver capsules of various sizes
- Application of sub-micromolar EA-irms: Concentration and δ13C of DOC in
sediment pore water (with DOC ~ 2 to 30 mg.L-1 and sample volume < 10 mL)
SLIDE 3 Instrumental setup
LLO-UMD setup:
- Thermo Delta Plus XL IRMS
- Conflo-II interface
- Costech ECS4010 with Pneumatic
autosampler EPS-Northwestern setup:
- Thermo Delta V Plus IRMS
- Conflo-IV interface
- Costech ECS4010 with Zero Blank
autosampler
SLIDE 4 Preparation of primary standard and DOC samples
- Primary DOC standards were prepared by dissolving IAEA CH-6
Sucrose (δ13C –10.45‰) in de-ionized water, to a concentration
- f 0.3 µg C. µL-1
- Between 1 and 40 µL of the primary standard solution were
loaded in tin capsules and oven dried at 60 °C for 8 hours
- 2 to 10 mL of sediment pore water samples were taken in pre-
combusted 10 mL glass vials, acidified to pH ~2 with dilute HCl, and evaporated to dryness in a vacuum oven at 60 °C. The residual organic matter were re-dissolved in 250 µL of de- ionized water, loaded in tin capsules and dried at 60 °C for 8 hours
- DOC concentrations of the pore water samples were measured
independently using a Shimadzu TOC Analyzer
SLIDE 5
Elemental Analyzer (Costech ECS4010) in CHN configuration
Elemental Analyzer Helium flow: 80 mL.min-1 4 m SS GC column @80°C Conflo (II / IV) Helium pressure: 1.2 bar 0% sample dilution MS ion-source Delta Plus XL Delta V Plus Emission 1.00 mA 1.50 mA Trap 20 V 40 V Electron energy 83 V 124 V Extraction 50% 85%
SLIDE 6
EA-irms analysis of IAEA CH-6 Sucrose: C peak areas
y = 5.510x y = 2.6x 10 20 30 40 50 60 70 80 2 4 6 8 10 12 14 16 18 20 22 24
Net area all [mV s] C [µg]
Delta V Plus Delta Plus XL 6 µg C Blank
SLIDE 7
Carbon backgrounds of tin and silver capsules
y = 3.3x y = 7.4x y = 13.0x y = 13.0x
10 20 30 40 50 60 1 2 3 4 5 6
Area all [mV s]
Number of capsules Tin (3 mm) Tin (5 mm) Tin (9 mm) Silver (5 mm)
Capsule type Background [µg C] Tin (3.5×5 mm)
0.6
Tin (5×9 mm)
1.4
Tin (9×10 mm)
2.4
Silver (5×9 mm)
2.4
SLIDE 8 Cleaned or un-cleaned tin capsules?
4.5 4.7 4.9 5.1 5.3 5.5 5.7 5.9
- 27.4
- 27.2
- 27.0
- 26.8
- 26.6
- 26.4
- 26.2
- 26.0
- 25.8
Area all [mV s] δ13C (‰)
SLIDE 9
EA-irms analysis of IAEA CH-6 Sucrose: δ13C results
(blank corrected)
Fitted curves: y = y0 + a*e-bx + c*e-dx
SLIDE 10
EA-irms analysis of IAEA CH-6 Sucrose: δ13C results
(corrected for non-linearity)
1σ (>3 mg C): ±0.11 ‰ (n = 15) ±0.15 ‰ (n = 21)
Correction eqn. : δ13Ccorr = δ13Cmeas – (y0 + a*e-bx + c*e-dx) + δ13CCH-6
SLIDE 11 Measurements of pore water DOC and δ13C
- Measured with Delta Plus XL IRMS with Pneumatic Autosampler
- Only for samples with > 3 µg C
SLIDE 12
DOC concentrations: IRMS vs TOC analyzer
y = 1.30x - 0.84 10 20 30 40 10 20 30 40
TOC Analyzer [mg C.L-1] IRMS [mg C.L-1]
DOC measured with IRMS were 30% lower than those with TOC analyzer (sample volatilization?)
SLIDE 13 Conclusions
- Both C amount and δ13C were analyzed in sub-micromolar range using a
commercial EA-irms without any significant modification
- Precision of δ13C were better than ±0.2‰ for samples with > 3 µg C
- Carbon background in untreated tin capsules range from 0.6 to 2.4 µg C
depending on size; silver capsules have ~ 75% more background C than tin
- Method applied to analyze concentration and δ13C of DOC in sediment
pore water samples
- Potential applications of sub-micromolar EA-irms (δ13C in trace non-
volatile solids):
- aerosols
- pollen grains
- single microfossil shells
SLIDE 14 Acknowledgements
Sincere thanks to:
- The organizing committee, ASITA
- Staffs of the Organic Geochemistry Lab, Large Lakes Observatory
- Staffs of the Dept. of Earth & Planetary Sciences, Northwestern University
