title: An Ultrahigh Precision, High-Frequency Dissolved Inorganic Carbon Analyzer Based on Dual Isotope Dilution and Cavity Ring-Down Spectroscopy.
abstract: We present a novel method for continuous and automated shipboard measurements of dissolved inorganic carbon concentration ([DIC]) in surface water. The method is based on dual isotope dilution and cavity ring-down spectroscopy (DID-CRDS). In this method, seawater is continuously sampled and mixed with a flow of NaH(13)CO3 solution that is also enriched in deuterated water (the spike). The isotopic composition of CO2 (δ(13)C(spiked_sample)) derived from the DIC in the mixture, and the D/H ratio of the mixed water (δD(spiked_sample)), are measured by CRDS analyzers. The D/H of the water in the mixture allows accurate estimates of the mixing ratio of the sample and the spike. [DIC] of the sample is then calculated from the mixing ratio, [DI(13)C] of the spike, and δ(13)C(spiked_sample). In the laboratory, the precision of the method is <0.02% (±0.4 μmol kg(-1) when [DIC] = 2000 μmol kg(-1)). A shipboard test was conducted in the Delaware Bay and Estuary. For 2 min average [DIC], a precision of <0.03% was achieved. Measurements from the DID-CRDS showed good agreement with independent measurements of discrete samples using the well-established coulometric method (mean difference = -1.14 ± 1.68 μmol kg(-1)), and the nondispersive infrared(NDIR)-based methods (mean difference = -0.9 ± 4.73 μmol kg(-1)).
authors.affiliation: †Earth and Ocean Science Division, Duke University, Durham, North Carolina 27708, United States.|‡Department of Geosciences, Princeton University, Princeton, New Jersey 08544, United States.|§Picarro Inc., Santa Clara, California 95054, United States.
authors.forename: Kuan
authors.initials: K
authors.lastname: Huang
authors.affiliation: †Earth and Ocean Science Division, Duke University, Durham, North Carolina 27708, United States.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Cassar
authors.affiliation: ‡Department of Geosciences, Princeton University, Princeton, New Jersey 08544, United States.
authors.forename: Bror
authors.initials: B
authors.lastname: Jonsson
authors.affiliation: ∥College of Earth, Ocean and Environment, Delaware University, Newark, Delaware 19716, United States.
authors.forename: Wei-jun
authors.initials: WJ
authors.lastname: Cai
authors.affiliation: ‡Department of Geosciences, Princeton University, Princeton, New Jersey 08544, United States.
authors.forename: Michael L
authors.initials: ML
authors.lastname: Bender
mesh_terms: D002244:Carbon / Q000032:analysis*; D002247:Carbon Isotopes; D007201:Indicator Dilution Techniques; D007287:Inorganic Chemicals / Q000032:analysis*; D054712:Salinity; D012623:Seawater / Q000737:chemistry; D012995:Solubility; D013057:Spectrum Analysis / Q000379:methods*; D013227:Steam / Q000032:analysis
chemical_list: D002247:Carbon Isotopes; D007287:Inorganic Chemicals; D013227:Steam; D002244:Carbon