Standard operating procedure for soil total carbon Dumas dry combustion method Global Soil Laboratory Network GLOSOLAN-SOP-03 GLOSOLAN SOIL TOTAL CARBON Version number : 1 Page 1 of 10 Dumas dry combustion method Effective date : October 28, 2019 SOIL TOTAL CARBON Dumas dry combustion method VERSION HISTORY N° Date Description of the modification Type of modification 01 30 July 2019 Finalization of the draft version Compilation of all inputs received by RESOLANs 02 28 October 2019 Final review of the SOP at the 3rd Revision of SOP steps, final GLOSOLAN meeting discussion and agreement 03 04 Etc. Modify by Revision Approved Date Validated Date GLOSOLAN SOP Tech. W.G. 3rd GLOSOLAN 3rd GLOSOLAN 27 October 2019 Leaders: F. Bertsch, Costa Rica, and M. meeting meeting Ostinelli, Argentina Global Soil Laboratory Network GLOSOLAN-SOP-03 GLOSOLAN SOIL TOTAL CARBON Version number : 1 Page 2 of 10 Dumas dry combustion method Effective date : October 28, 2019 Contents 1. Brief introduction to total carbon..................................................................................................... 3 2. Scope and field of application ........................................................................................................... 3 3. Principle .............................................................................................................................................. 3 4. Apparatus ........................................................................................................................................... 4 5. Materials ............................................................................................................................................. 4 6. Health and safety ............................................................................................................................... 4 7. Sample preparation ........................................................................................................................... 4 8. Procedure ........................................................................................................................................... 5 8.1. Calibration of the apparatus ...................................................................................................... 5 8.2. Determination of the total carbon (TC) content ....................................................................... 5 9. Calculation .......................................................................................................................................... 5 10. Quality assurance/Quality control ................................................................................................. 5 10.1. Precision test ............................................................................................................................. 5 10.2. Trueness test ............................................................................................................................. 6 10.3. Control chart ............................................................................................................................. 7 11. Reference documents ...................................................................................................................... 7 12. Appendix I.—Acknowledgments .................................................................................................... 8 13. Appendix II.—List of authors .......................................................................................................... 8 14. Appendix III.—Contributing laboratories ..................................................................................... 8 Modify by Revision Approved Date Validated Date GLOSOLAN SOP Tech. W.G. 3rd GLOSOLAN 3rd GLOSOLAN 27 October 2019 Leaders: F. Bertsch, Costa Rica, and M. meeting meeting Ostinelli, Argentina Global Soil Laboratory Network GLOSOLAN-SOP-03 GLOSOLAN SOIL TOTAL CARBON Version number : 1 Page 3 of 10 Dumas dry combustion method Effective date : October 28, 2019 1. Brief introduction to total carbon Analysis and quantification of total soil carbon (TC) is necessary to estimate soil organic matter content, which is a useful parameter when evaluating the productivity of a natural system. Quantification of TC can be used to monitor soil carbon (C) stocks and to evaluate the role and effectiveness of C sequestration to mitigate climate change. Several methods are used to quantify soil C. The Dumas dry combustion method determines total carbon, representing all chemical forms of C in the soil. Other methods may be used to quantify the various forms of carbon. For example, the Walkley & Black method measures oxidizable organic carbon. For analysis of TC by dry combustion, an automatic chemical analyser, commonly known as an autoanalyzer, is used. Advantages of using an autoanalyzer are increased accuracy and versatility. An autoanalyzer can be used to quantify carbon, nitrogen, and sulfur. Disadvantages of using an autoanalyzer are equipment initial cost, operating and maintenance costs, and the lower number of labs using an autoanalyzer worldwide. Additional care must be taken during sample preparation if quantifying TC by the Dumas dry combustion method. A very small sample is used, which requires the samples to be well homogenized. 2. Scope and field of application This standard operating procedure (SOP) describes, in general terms, quantification of TC content in soil samples by an autoanalyzer. The procedure measures both organic C and inorganic C together. To quantify the organic C fraction only, the inorganic C fraction must be removed or quantified prior to autoanalyzer analysis. Alternatively, the inorganic C can be quantified separately and then subtracted from the TC. 3. Principle This method is based on the Dumas dry combustion principle. The sample is burned at high temperature (between 900 and 1000 °C or 1400 and 1600 °C) in an atmosphere of pure oxygen. Under these conditions, all C-containing compounds are completely decomposed and converted into carbon oxides (mainly carbon dioxide). The autoanalyzer measures and reports the TC value based on the concentration of carbon oxides present using various procedures (for example, a C gas detector and thermal differences between gas columns). Modify by Revision Approved Date Validated Date GLOSOLAN SOP Tech. W.G. 3rd GLOSOLAN 3rd GLOSOLAN 27 October 2019 Leaders: F. Bertsch, Costa Rica, and M. meeting meeting Ostinelli, Argentina Global Soil Laboratory Network GLOSOLAN-SOP-03 GLOSOLAN SOIL TOTAL CARBON Version number : 1 Page 4 of 10 Dumas dry combustion method Effective date : October 28, 2019 4. Apparatus 1. Autoanalyzer for C, with all specific accessories and consumables, including appropriate detection system. The equipment might also analyse N and S, depending on the manufacturer and model. 2. Analytical balance, ±0.0001 g, to weigh samples and reference materials. 3. Milling system that meets the requirements of the autoanalyzer manufacturer. 4. Crucible set (if needed), depending on the sample size used by the autoanalyzer. 5. Materials 1. Certified Reference Material (CRM) with known C content to calibrate the autoanalyzer. The CRM may vary depending on autoanalyzer manufacturer. Aspartic acid, EDTA, acetanilide, or soil samples with certified total C content may be used. 2. Oxygen gas (O2), along with reference or carrier gases (He, for example), of very high purity (greater than 99.99%). 3. Consumables specific to the autoanalyzer. 6. Health and safety This SOP does not imply the direct use of dangerous chemical reagents, but appropriate safety precautions are necessary. Catalyser residues are toxic and must be disposed of properly. Gloves, lab coats, and eye protection must be worn when handling reagents and samples. When a special reagent is used (for example, a reference material for equipment control), consult the material safety data sheet (MSDS) and conduct a risk assessment. Take necessary precautions when handling compressed gasses and high-temperature equipment. Follow the manufacturer’s safety guidelines when operating the autoanalyzer. 7. Sample preparation Follow the sample preparation instructions provided by the manufacturer for use of the autoanalyzer. Probably, a representative portion of the soil sample that was previously treated (dried and sieved to 2 mm) must be porfirised (grind fine and homogeneously) until the entire fraction passes through a sieve of inferior size. Typically, a representative subsample is taken from the bulk sample and milled to a sufficiently fine mesh size. Ensure that milling equipment and sieves do not introduce contamination to the samples. Modify by Revision Approved Date Validated Date GLOSOLAN SOP Tech. W.G. 3rd GLOSOLAN 3rd GLOSOLAN 27 October 2019 Leaders: F. Bertsch, Costa Rica, and M. meeting meeting Ostinelli, Argentina Global Soil Laboratory Network GLOSOLAN-SOP-03 GLOSOLAN SOIL TOTAL CARBON Version number : 1 Page 5 of 10 Dumas dry combustion method Effective date : October 28, 2019 8. Procedure 8.1. Calibration of the apparatus Calibrate the equipment as described in the autoanalyzer instruction manual. Use a CRM provided or recommended by the manufacturer (soil, acetanilide, calcium carbonate, EDTA, glucose anhydrous, etc). The CRM should cover the range of TC typically found in test samples. Store all CRM as indicated by the manufacturer label. Replicated blanks must also be analysed to determine the baseline according the specific equipment