Simplified coulometric method for multi-sample measurements of total dissolved inorganic carbon concentration in marine waters

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. Analyst2014, 139, 5263 - 5270.