Total, Organic and Inorganic carbon concentration data

This dataset supports the manuscript "Comparing accuracy and precision of Loss on Ignition and Elemental Analysis when quantifying organic carbon concentrations" by Sparkes et al.

Accurate and precise measurements of sedimentary carbon concentrations, including total carbon (TC) and the organic (OC) and inorganic (IC) fractions, are vital foundations of research across the Earth and environmental sciences, and are also critical for regulatory monitoring, reporting and verification of carbon stocks. Multiple methods exist for measuring carbon concentrations in complex solid mixtures, but many disciplines lack a consensus approach, which restricts cross-study comparisons. This study rigorously tested three common protocols using a combination of certified reference materials (CRM) and real-world samples (agricultural soil and intertidal sediments). Total carbon was measured by loss-on-ignition (LoI) and elemental analysis (EA); LoI results were precise but required calibration when converting mass loss to organic and inorganic carbon content, and calibrations including addition or subtraction of a constant value were not appropriate at low carbon concentrations. EA was precise and accurate method when measuring total carbon. To differentiate OC and IC using the elemental analyser, two pre-treatments were tested. Combustion of organic matter (500 °C, 12 hours) prior to EA gave accurate and precise IC and OC measurements but pre-treating with 1N hydrochloric acid to remove carbonate also led to organic carbon loss, giving reduced accuracy and precision. Nine independent measurements on a homogenised soil sample showed that combustion-EA and LoI were precise and repeatable, with relative standard deviations <3%, whilst OC and IC results from acid decarbonation-EA showed greater variability between repeats (>5%) and a loss of OC during decarbonation.
Paired EA measurements using both pre-treatment techniques were carried out on saltmarsh sediment samples from around England to test the relationship between OC measurement protocols. Acid decarbonation-EA reported significantly lower OC values than combustion-elemental analysis, by 1.09 ± 0.73 wt%. No consistent absolute or relative differences were observed, therefore a universal equation to align results from the two techniques was not derivable.
Overall, we recommend that elemental analysis is used as the standard method for TC quantification in soil and sediment samples. When separate IC and OC values are required, combustion-EA is the preferred technique, due to its high accuracy and precision.