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Total Carbon, Nitrogen and Protein - Combustion Method

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Total Carbon, Nitrogen and Protein - Combustion Method

Summary

This analytical method quantitatively determines the total amount of nitrogen and carbon using an instrument that utilizes a combustion system with an induction furnace coupled with a thermal conductivity detector (TCD) system and an IR detector system. The method is based on the oxidation of the sample by “flash combustion” which converts all organic and inorganic substances into combustion gases (N2, NOx, CO2, and H2O). The method has a detection limit of approximately 0.02% for nitrogen and 0.02% for carbon.

Total crude protein is calculated from the nitrogen content of the material, based on sample type. The protein factor applied to the nitrogen result is 6.25 unless a different factor is requested. The method has a detection limit of 0.1% protein.

If total organic carbon is requested (only appropriate for compost), total inorganic carbon (TIC) is quantitatively determined by measuring the calcium carbonate content using gravimetric analysis and then using a factor of 0.12 to convert calcium carbon to total inorganic carbon (TIC). Total organic carbon (TOC) is calculated as the difference between total carbon and total inorganic carbon. The method has a detection limit of approximately 0.02% carbon.

Sample preparation is dependent on matrix. Contact the lab for further information.

  • Sample amount requested: CN, Protein - 5 g dry / 10 mL liquid; CN, TOC - 30 g dry
  • Questions concerning limited sample size can be answered by the UC Davis Analytical Laboratory.

References:

  • AOAC Official Method 972.43, Microchemical Determination of Carbon, Hydrogen, and Nitrogen, Automated Method, in Official Methods of Analysis of AOAC International, 16th Edition (1997), Chapter 12, pp. 5-6, AOAC International, Arlington, VA.
  • Western Region Method S 9.30, Total Nitrogen and Organic Carbon – Combustion Method); Soil, Plant and Water Reference Methods for the Western Region, WREP-125, 4th Edition, 2013.
  • AOAC Official Method 990.03, Protein (Crude) in Animal Feed, Combustion Method, in Official Methods of Analysis of AOAC International, 18th edition Revision 1, 2006. Chapter 4, pp. 30-31, AOAC International, Gaithersburg, MD.
  • Western Region Method S 13.10, Soil Carbonate – Gravimetric Determination); Soil, Plant and Water Reference Methods for the Western Region, WREP-125, 4th Edition, 2013.