Practical steps for improved estimates of calcium carbonate concentrations in deep sea sediments using coulometry

Carl-Magnus Mörth, Jan Backman

Limnol. Oceanogr. Methods 9:565-570 (2011) | DOI: 10.4319/lom.2011.9.565

ABSTRACT: Coulometric titration is a commonly used method for determination of carbonate carbon, and hence calcium carbonate concentrations, in geological materials. Analyzes of 460 samples of pure CaCO3 powder demonstrate that the coulometer output data need to be recalculated using a multi-point regression analysis. These analyses also demonstrate that to generate a precision of ±0.8%, at least 7 mg of 100% calcite is needed. A precision of ± 0.5% requires 12 mg pure calcite. We recommend that 35 mg samples are used for most deep sea sediment samples, which gives a precision of ±0.8% down to 20% calcite contents in the sample. Calcite contents <10% in samples require multiple runs to improve precision.