Improved Characterization of Soil Organic Matter by Thermal Analysis Using CO2/H2O Evolved Gas Analysis

Simultaneous thermal analysis [i.e., thermogravimetry (TG) and differential scanning calorimetry (DSC)] is frequently used in materials science applications and is increasingly being used to study soil organic matter (SOM) stability. Yet, important questions remain, especially with respect to how the soil mineral matrix affects TG-DSC results, which could confound the interpretation of relationships between thermal and biogeochemical SOM stability. The objective of this study was to explore the viability of using infrared gas analyzer (IRGA) based CO2/H2O evolved gas analysis (EGA) as a supplement or alternative to TG-DSC to improve the characterization of SOM. Here, we subjected reference samples and a set of 28 diverse soil samples from across the U.S. to TG-DSC coupled with IRGAbased EGA. The results showed the technical validity of coupling TG-DSC and CO2-EGA, with more than 80% of the theoretically evolved CO2-C recovered during pure cellulose and CaCO3 analysis. CO2-EGA and DSC thermal profiles were highly similar, with correlation coefficients generally >0.90. Additionally, CO2/H2O-EGA proved useful to improve the accuracy of baseline correction, detect the presence of CaCO3 in soils, and identify SOM oxidative reactions normally hidden in DSC analysis by simultaneous endothermic reactions of soil minerals. Overall, this study demonstrated that IRGA-based CO2/H2O-EGA constitutes a valuable complement to conventional TG-DSC analysis for SOM characterization.