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

Abstract

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 but field sample analyses suggest that prefiltering may be necessary in highly turbid waters.