Determination of Organic Carbon in Soil and Sediment by the Elemental Analyzer with Silver Cup Digestion Method

Soil organic carbon (SOC) is an important indicator of soil health and ecosystem functioning and is of great significance for agricultural production and environmental protection. Accurate determination of SOC content is essential for assessing soil quality, optimizing fertilizer management, improving crop yields, and contributing greatly in the research of tackling climate change as well as the carbon cycle. A rapid and accurate method for the determination of organic carbon in soil and sediment was established to support scientific research and agricultural production. The silver cup digestion-elemental analyzer method was used to process soil samples using 81-porosity copper plates and silver cups by optimizing sample pretreatment, including acid concentration and volume, sample weight as well as digestion temperature. The specific procedure was initially weighing 25mg of sample using Φ5mm×9mm silver cups, then adding 80µL of 2mol/L hydrochloric acid to remove inorganic carbon, followed by drying the sample on an electric hot plate at 70℃. Samples with high inorganic carbon were treated by repeated acid addition. Low and high content standards were used to form a mixed standard curve to quantify the organic carbon with a daily calibration method. The method demonstrated excellent linearity in the range of 21.2−6704.3μg of organic carbon content with a linear correlation coefficient of 0.9998. The limits of detection (LOD) and quantification (LOQ) of the method were 0.07% and 0.23%, respectively, based on a sample weight of 25mg. The precision of organic carbon determined for six standard substances (GBW07406, GBW07385, GBW07391, GBW07544, GBW07544, GBW07546 and GBW07365) ranged from 0.67% to 5.14%, with all measured values falling within the range of the standard values. The method demonstrates high precision and accuracy, which meets the requirements for the determination of organic carbon in soil and sediment and is suitable for the analysis of large quantities of samples.