EA-irms of sub-micromolar C samples: Concentration and 13 C of DOC - PowerPoint PPT Presentation

EA-irms of sub-micromolar C samples: Concentration and δ 13 C 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

Objectives Elemental Analyzers coupled with IRMS in their “standard configuration” • typically require samples with ~ 30 to 600 µ g carbon for δ 13 C 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 δ 13 C of DOC in • sediment pore water (with DOC ~ 2 to 30 mg.L -1 and sample volume < 10 mL)

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

Preparation of primary standard and DOC samples Primary DOC standards were prepared by dissolving IAEA CH-6 • Sucrose ( δ 13 C –10.45‰) in de-ionized water, to a concentration of 0.3 µ g C. µ L -1 Between 1 and 40 µ L 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 µ L 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

Elemental Analyzer (Costech ECS4010) in CHN configuration Helium flow: 80 mL.min -1 Elemental Analyzer 4 m SS GC column @80°C Helium pressure: 1.2 bar Conflo (II / IV) 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%

EA-irms analysis of IAEA CH-6 Sucrose: C peak areas 80 Delta V Plus Delta Plus XL 70 60 Net area all [mV s] 50 y = 2.6x 40 y = 5.510x 30 20 6 µ g C 10 0 0 2 4 6 8 10 12 14 16 18 20 22 24 Blank C [ µ g]

Carbon backgrounds of tin and silver capsules 60 Tin (3 mm) Tin (5 mm) y = 13.0x 50 Tin (9 mm) y = 13.0x Silver (5 mm) 40 Area all [mV s] y = 7.4x 30 Capsule Background [ µ g C] type 20 Tin (3.5×5 mm) 0.6 y = 3.3x Tin (5×9 mm) 1.4 10 Tin (9×10 mm) 2.4 0 Silver (5×9 mm) 2.4 0 1 2 3 4 5 6 Number of capsules

Cleaned or un-cleaned tin capsules? 5.9 5.7 5.5 Area all [mV s] 5.3 5.1 4.9 4.7 4.5 -27.4 -27.2 -27.0 -26.8 -26.6 -26.4 -26.2 -26.0 -25.8 δ 13 C (‰)

EA-irms analysis of IAEA CH-6 Sucrose: δ 13 C results (blank corrected) Fitted curves: y = y 0 + a*e -bx + c*e -dx

EA-irms analysis of IAEA CH-6 Sucrose: δ 13 C results (corrected for non-linearity) 1 σ (>3 mg C): ±0.11 ‰ (n = 15) ±0.15 ‰ (n = 21) Correction eqn. : δ 13 C corr = δ 13 C meas – (y 0 + a*e -bx + c*e -dx ) + δ 13 C CH-6

Measurements of pore water DOC and δ 13 C Measured with Delta Plus XL IRMS with Pneumatic Autosampler • Only for samples with > 3 µ g C •

DOC concentrations: IRMS vs TOC analyzer 40 30 TOC Analyzer [mg C.L -1 ] DOC measured with IRMS were 30% lower than those with TOC 20 analyzer (sample volatilization?) y = 1.30x - 0.84 10 0 0 10 20 30 40 IRMS [mg C.L -1 ]

Conclusions Both C amount and δ 13 C were analyzed in sub-micromolar range using a • commercial EA-irms without any significant modification Precision of δ 13 C were better than ±0.2‰ for samples with > 3 µ g C • Carbon background in untreated tin capsules range from 0.6 to 2.4 µ g C • depending on size; silver capsules have ~ 75% more background C than tin Method applied to analyze concentration and δ 13 C of DOC in sediment • pore water samples Potential applications of sub-micromolar EA-irms ( δ 13 C in trace non- • volatile solids): aerosols • pollen grains • single microfossil shells •

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 •