RADIOCARBON IN DISSOLVED ORGANIC CARBON BY UV OXIDATION: PROCEDURES AND BLANK CHARACTERIZATION AT NOSAMS

Radiocarbon ◽  
2020 ◽  
pp. 1-18
Author(s):  
Li Xu ◽  
Mark L Roberts ◽  
Kathryn L Elder ◽  
Mark D Kurz ◽  
Ann P McNichol ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Photochemical Oxidation ◽  
Oxidation Method ◽  
Procedural Blank ◽  
Ocean Sciences ◽  
Mass Spectrometry Facility ◽  
Best Fit ◽  
Uv Oxidation

ABSTRACT This study describes a procedural blank assessment of the ultraviolet photochemical oxidation (UV oxidation) method that is used to measure carbon isotopes of dissolved organic carbon (DOC) at the National Ocean Sciences Accelerator Mass Spectrometry Facility (NOSAMS). A retrospective compilation of Fm and δ13C results for secondary standards (OX-II, glycine) between 2009 and 2018 indicated that a revised blank correction was required to bring results in line with accepted values. The application of a best-fit mass-balance correction yielded a procedural blank of 22.0 ± 6.0 µg C with Fm of 0.30 ± 0.20 and δ13C of –32.0 ± 3.0‰ for this period, which was notably higher and more variable than previously reported. Changes to the procedure, specifically elimination of higher organic carbon reagents and improved sample and reactor handling, reduced the blank to 11.0 ± 2.75 µg C, with Fm of 0.14 ± 0.10 and δ13C of –31.0 ± 5.5‰. A thorough determination of the entire sample processing blank is required to ensure accurate isotopic compositions of seawater DOC using the UV oxidation method. Additional efforts are needed to further reduce the procedural blank so that smaller DOC samples can be analyzed, and to increase sample throughput.

scholarly journals Total Uncertainty of Radiocarbon Measurements of Marine Dissolved Organic Carbon and Methodological Recommendations

Radiocarbon ◽  
2013 ◽  
Vol 55 (3) ◽  
pp. 1135-1141 ◽  
Author(s):  
Ellen R M Druffel ◽  
Sheila Griffin ◽  
Brett D Walker ◽  
Alysha I Coppola ◽  
Danielle S Glynn
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Water Systems ◽  
Energy Agency ◽  
Total Uncertainty ◽  
Oxidation Method ◽  
Sample Water ◽  
Pvc Pipe ◽  
Carbon Concentrations ◽  
Uv Oxidation

We report results of duplicate measurements of dissolved organic carbon concentrations ([DOC] as μM) and Δ14C in seawater in order to assess the total uncertainty of reported [DOC] and Δ14C measurements via the UV oxidation method. In addition, pure International Atomic Energy Agency standards analyzed over a 4-yr period are evaluated. We find the total uncertainty of Δ14C measurements to be ±4.0. However, in samples that were thawed, subsampled, and refrozen prior to UV oxidation, the total uncertainty of Δ14C measurements is on the order of ±10. The [DOC] measurements of these samples were also higher by 1.8 ± 0.3 μM. The reason(s) for these documented increases in total [DOC] and Δ14C uncertainty are unclear. In order to minimize any effects on sample measurements, we recommend the following: 1) regular monitoring of duplicate samples, DOC standards, and diluent (Milli-Q™) water for Δ14C and [DOC] measurements; 2) thawing a sample immediately and only once prior to UV oxidation; 3) avoid the use of DOC-leachable plumbing (such as PVC pipe) in both water systems feeding and within Milli-Q systems; and 4) consider the use of DOC-free diluents (i.e. pre-UV oxidized Milli-Q or sample water).

scholarly journals An Alternate Method of Diluting Dissolved Organic Carbon Seawater Samples for 14C Analysis

Radiocarbon ◽  
2010 ◽  
Vol 52 (3) ◽  
pp. 1224-1229 ◽  
Author(s):  
Sheila Griffin ◽  
Steven R Beaupré ◽  
Ellen R M Druffel
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Small Volume ◽  
High Concentration ◽  
Preparation Time ◽  
Time Saving ◽  
Oxidation Method ◽  
Doc Concentration ◽  
Seawater Samples ◽  
Uv Oxidation

We present a time-saving modification to the ultraviolet (UV) oxidation method for analyzing dissolved organic carbon (DOC) concentration, Δ14C, and δ13C measurements in seawater and standard materials. A low background (∼0.2 ± 0.2 μM) was reported for pre-irradiated Milli-Q (MQ) water that was used to dilute samples for DOC 14C analysis (Beaupré et al. 2007). We use MQ water without pre-irradiation (background ∼0.9 ± 0.2 μM) to dilute the sample. This method is suitable for small-volume, high-concentration samples (mass of sample DOC overwhelms mass of MQ water DOC). An acceptable precision of Δ14C measurements (5–9‰) is maintained. This revised method reduces the preparation time for diluted DOC Δ14C samples from 2 days to 1 day.

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