Article pubs.acs.org/est
An Ultrahigh Precision, High-Frequency Dissolved Inorganic Carbon Analyzer Based on Dual Isotope Dilution and Cavity Ring-Down Spectroscopy Kuan Huang,*,†,‡,§ Nicolas Cassar,† Bror Jonsson,‡ Wei-jun Cai,∥ and Michael L. Bender‡ †
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 ∥ College of Earth, Ocean and Environment, Delaware University, Newark, Delaware 19716, United States ‡
S Supporting Information *
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 NaH13CO3 solution that is also enriched in deuterated water (the spike). The isotopic composition of CO2 (δ13Cspiked_sample) derived from the DIC in the mixture, and the D/H ratio of the mixed water (δDspiked_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, [DI13C] of the spike, and δ13Cspiked_sample. In the laboratory, the precision of the method is
