Measurement of organic and inorganic carbon in dolomite-containing samples

It is still open to question which method is the best for quantifying organic carbon (OC) and inorganic carbon (IC) in soils containing dolomite. The aims of this study were (1) to compare the accuracy of a novel thermal gradient (ThG), the classical calcimeter (CALC) and the loss-on-ignition (LOI) methods on a reference sample set with known proportions of OC present as soil organic matter (SOM) and IC present as dolomite and (2) to compare the results of the different methods on a set of soil samples with different dolomite and SOM contents. The CALC and LOI methods rely on separate quantification or removal of IC by acid or heat, whereas IC and OC can be quantified in a single run by the ThG analysis. The ThG method was the most accurate method for the reference sample set, especially when dolomite contents were high. On the soil sample set, the ThG and CALC methods performed equally well, but only when two outliers were eliminated. The LOI method was not satisfactory for either sample set. Overall, ThG was the most reliable method for measuring IC and OC in dolomite-containing samples over a wide range of concentrations, but the more widely used CALC method was also acceptable.