Kjeldahl Digestion for Total Nitrogen
- DIGESTION MIXTURE - 3 kg K2S04 and 600 g CuS04.5H20 (or 384 g CuS04 anhydrous) (use CuS04.5H20 if available). (This mixture can be purchased as Kjeltab catalyst tablets.)
- CONC H2S04.
- NITROGEN STANDARD - Accurately weigh 4.7166 g (NH4)2S04 (dried and stored in the desiccator), dissolve in deionized water, then dilute to 100 mL. This will give you a 1% N solution. To check distillation procedure, pipet 1 mL into digestion tube, dilute with about 80 mL deionized water and follow the distillation procedure. For calculations, 1 mL = 1 g.
- Glycine - Weigh 0.1000 mg (stored in desiccator) and digest along with samples. Value should be 18.66 + 0.9% N.
- DIGESTION BLOCK
- FUME MANIFOLD
- 250 mL DIGESTION TUBES
- Weigh 0.500 g plant tissue or 0.500 g feed sample into a 250 mL digestion tube.
- Add 2 Kjeltab catalyst tablets.
- Add 12 mL of conc. H2S04.
- Place on digestion block with front and back shields.
- Heat at 400oC for 45 min. (should be 30 min. after samples have cleared).
- Remove from block and allow to cool 15 - 20 min. with shields off.
- Add approximately 75 mL dH20.
- Sample is ready for distillation.
- Ash 0.1 g glycine along with samples on first set. Ensure value of N is 18.66 + 0.9%.
- Prior to distilling samples, pipet 1 mL of (NH4)2SO4 solution into a digestion tube for each distillation unit, dilute each with 80 mL deionized water, and distill to ensure each sample is 1.00 + 0.05% N.
- Brenner, J. M. 1965. Total Nitrogen. In C. A. Black (ed) Methods of Soil Analysis, Part II, SSSA., Madison, Wis. p.1149-1178.
- Horwitz, W. (ed). 1970. Official Methods of Analysis of the AOAC, 11th Edition, Washington, D. C. p.16-17.
- Tecator Manual. Kjeltec System 2300 Distilling Unit. Tecator, Hoganas, Sweden.