title: Carbon isotope analysis of dissolved organic carbon in fresh and saline (NaCl) water via continuous flow cavity ring-down spectroscopy following wet chemical oxidation.
abstract: This work examines the performance and limitations of a wet chemical oxidation carbon analyser interfaced with a cavity ring-down spectrometer (WCO-CRDS) in a continuous flow (CF) configuration for measuring δ(13)C of dissolved organic carbon (δ(13)C-DOC) in natural water samples. Low-chloride matrix (<5 g Cl/L) DOC solutions were analysed with as little as 2.5 mg C/L in a 9 mL aliquot with a precision of 0.5 ‰. In high-chloride matrix (10-100 g Cl/L) DOC solutions, bias towards lighter δ(13)C-DOC was observed because of incomplete oxidation despite using high-concentration oxidant, extended reaction time, or post-wet chemical oxidation gas-phase combustion. However, through a combination of dilution, chloride removal, and increasing the oxidant:sample ratio, high-salinity samples with sufficient DOC (>22.5 µg C/aliquot) may be analysed. The WCO-CRDS approach requires more total carbon (µg C/aliquot) than conventional CF-isotope ratio mass spectrometer, but is nonetheless applicable to a wide range of DOC concentration and water types, including brackish water, produced water, and basinal brines.
authors.affiliation: a USGS National Research Program , Menlo Park , CA , USA.
authors.forename: Christopher H
authors.initials: CH
authors.lastname: Conaway
authors.forename: Burt
authors.initials: B
authors.lastname: Thomas
authors.forename: Nabil
authors.initials: N
authors.lastname: Saad
authors.forename: James J
authors.initials: JJ
authors.lastname: Thordsen
authors.forename: Yousif K
authors.initials: YK
authors.lastname: Kharaka
mesh_terms: D002247:Carbon Isotopes / Q000032:analysis; D005618:Fresh Water / Q000032:analysis*; D006812:Humic Substances / Q000032:analysis*; D013058:Mass Spectrometry / Q000379:methods*; D010084:Oxidation-Reduction; D012623:Seawater / Q000032:analysis*
chemical_list: D002247:Carbon Isotopes; D006812:Humic Substances
keywords: carbon-13; cavity ring-down spectroscopy; isotope hydrology; isotope measurements; methods and equipment; wet chemical oxidation