The Total Kjeldahl Nitrogen (TKN) method is based on the wet oxidation of soil organic matter and botanical materials using sulfuric acid and digestion catalyst and conversion of organic nitrogen to the ammonium form. Ammonium is determined using the diffusion-conductivity technique. The procedure does not quantitatively digest nitrogen from heterocyclic compounds (bound in a carbon ring), oxidized forms such as nitrate and nitrite, or ammonium from within mineral lattice structures. The method has a detection limit of approximately 0.001 % N.
Sample material must be ground to a powder fine enough to pass through a 60 mesh screen (<0.25 mm).
Sample amount requested: 3 g
Questions concerning limited sample size can be answered by the UC Davis Analytical Laboratory.
Note: SOP 315 (Soil Method) and SOP 515 (Plant Method) are identical.
Horneck, D. A. and Miller, R. O. 1998. Determination of Total Nitrogen in Plant Tissue pp. 75-83. In: Kalra, Y. P. (ed.) Handbook of Reference Methods for Plant Analysis, CRC Press, New York.
Isaac, R. A. and Johnson, W. C. 1976. Determination of total nitrogen in plant tissue, using a block digestor. J. Assoc. Off. Anal. Chem. 59:1 98-100.