An autonomous instrument for time series analysis of TCO2 from oceanographic moorings
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The design and testing of a robotic analyzer for autonomous TCO2 measurement from oceanographic moorings is described. The analyzer employs a conductimetric method of TCO2 measurement wherein CO2 from an acidified sample diffuses across a semi-permeable membrane into a NaOH solution decreasing the conductivity of the base. The instrument is capable of ~850 analyses over a period of at least six months. It is designed to operate to depths of at least 1000m. TCO2 calibration is based on in situ standardization throughout a deployment. We report both laboratory and in situ tests of the analyzer. In the laboratory automated analyses over a period of 38 days at temperatures ranging from 8° to 25° C yielded a TCO2 accuracy and precision of ±2.7 μmol/kg. In situ tests were conducted at the WHOI dock with a deployment of 8 weeks at in situ temperatures of 5°-13°C. The accuracy and precision of TCO2 analyses over the deployment period, based on in situ calibration, was ±3.6 μmol/kg. Laboratory tests of reagent and standard solution stability are also reported. Standards, based on Certified Reference Material were followed for periods of up to 2 years. In all cases TCO2 increased. Drift of the standards was the equivalent of ~1 to μmol/kg per 6 months. The conductivity indicator solution was found to be stable for at least 2 months.
Author Posting. © Elsevier B.V., 2009. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part I: Oceanographic Research Papers 56 (2009): 1590-1603, doi:10.1016/j.dsr.2009.04.006.
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