Dissolved inorganic carbon (DIC) is defined as the sum of the concentrations of dissolved CO2, carbonic acid, bicarbonate, and carbonate. DIC concentration, [DIC], is reported as micromoles carbon per kilogram of seawater (μmol kg-1). Seawater [DIC] typically range from 1800 to 2300 μmol kg-1 , but can reach 4300 μmol kg-1 in extreme marine environments (e.g. the Black Sea). For investigating the oceanic component of the global carbon cycle the consensus analytical goal is 0.05% for accuracy and precision, or 1.0 μmol kg-1 for seawater.
A new system requiring greatly reduced operator intervention has been developed for the determination of dissolved inorganic carbon concentration in marine waters. Based on a coulometric method, the system has an accuracy and precision comparable to more complex and expensive methods currently employed. A syringe pump equipped with a 12-port distribution valve is used to precisely dispense an acid solution and sample into a gas stripper. The system can autonomously measure eight discrete samples in duplicate or triplicate with no operator input. The best precision (%RSD) obtained was 0.022% (n = 14) or less than 1.0 μmol kg-1. The system is calibrated against a certified reference material (CRM). Average offset from the CRM was 1.2 μmol kg-1. Sample throughput was 4 samples per h. Carryover effects are negligible.
The Multi-sample Automated Natural sample Analyzer (MANA) and the interior of
the temperature regulated chamber housing the syringe and sample bottles.
(1) Amornthammarong, N.; Ortner, P.B.; Hendee, J.; Woosley, R. Analyst, 2014, 139, 5263 - 5270.