Rapid ¹⁴C Analysis of Dissolved Organic Carbon in Non-Saline Waters

Abstract

23The 14 C content of dissolved organic carbon (DOC) in rivers, lakes, and other non-saline waters 24 can provide valuable information on carbon cycling dynamics in the environment. DOC is 25 typically prepared for 14 C analysis by accelerator mass spectrometry (AMS) either by UV 26 oxidation or by freeze-drying and sealed tube combustion. We present here a new method for the 27 rapid analysis of 14 C of DOC using wet chemical oxidation (WCO) and automated headspace 28 sampling of CO2. The approach is an adaption of recently developed methods using aqueous 29 persulfate oxidant to determine the δ 13 C of DOC in non-saline water samples and the 14 C content 30 of volatile organic acids. One advantage of the current method over UV oxidation is higher 31 throughput: 22 samples and 10 processing standards can be prepared in one day and analyzed in a 32 second day, allowing a full suite of 14 C processing standards and blanks to be run in conjunction 33 with samples.

Comprehensive radiocarbon analysis of benzene polycarboxylic acids (BPCAs) derived from pyrogenic carbon in environmental samples

“…Further precautionary steps, such as UV oxidation of water immediately prior to use, are therefore recommended to minimize this potential source of contamination. Lang et al (2016) showed that the contamination from WCO can be as low as 0.68 µg C which is at least consistent with blank values reported for the other combustion techniques and would result in a total contamination of 1.33 µg C if attained in this study. Additionally, this study used the same experimental setup as Lang et al (2013) of 5 mL solvent (sample and oxidant in water) in 12 mL Exetainer vials yet, this could possibly be reduced to 3 mL solvent.…”

“…The screwcapped vials were then purged with ultra high purity helium at 100 mL min -1 for 8 min. Oxidation of the samples is achieved by placing the vials in a heating block at 95°C for 1 hr (Lang et al 2016). Measurement: Gas Ion Source AMS Gaseous samples were measured with a MIni CArbon DAting System (MICADAS, Ionplus, Switzerland) AMS fitted via a carbonate handling system modified with a needle for sparging solutions Wacker et al 2013).…”

“…Briefly, sample CO 2 (10-100 µg C) was sparged from the solution in septa-sealed vials onto a zeolite molecular sieve trap. The CO 2 gas was subsequently thermally desorbed and transferred to a gas-tight syringe with helium, then slowly injected into the gas-accepting ion source of the AMS at a constant rate (Lang et al 2016). The measurement time was set to a maximum of 8 min in order to attain a precision of better than 1% on modern standard.…”

“…In small-scale 14 C analyses, the total mass measured comprises the mass of the sample and the mass of the contaminant, the latter of which can be assessed via external process standards of known F 14 C, as well as via spiked process blanks (Lang et al 2016;Pearson et al 1998;Ziolkowski and Druffel 2009). Encompassing the entire BPCA 14 C analysis, the process standard charcoals yield a constant contamination of 3.50 ± 0.35 µg C and 0.443 ± 0.044 F A few studies have previously reported extraneous carbon in CSRA using either a different methodological setup or only certain subprocedures of multistep analyses.…”

“…Encompassing the entire BPCA 14 C analysis, the process standard charcoals yield a constant contamination of 3.50 ± 0.35 µg C and 0.443 ± 0.044 F A few studies have previously reported extraneous carbon in CSRA using either a different methodological setup or only certain subprocedures of multistep analyses. For example, Lang and collaborators reported a total contamination for the same WCO procedure of 0.68 ± 0.26 to 1.05 ± 0.23 µg C and 0.027 ± 0.015 to 0.107 ± 0.051 F 14 C (Lang et al 2016). The feasibility study by Gierga and collaborators that provides the foundation for the present approach assessed the uncertainties from AMS as well as WCO, found a contamination of 1.6 ± 0.2 µg C and 0.90 ± 0.14 F 14 C (Gierga et al 2014).…”