Kjeldahl’s method

Example Figure 3.1, represents the absolute errors in nitrogen analysis by means of micro Kjeldahl s Method. Here, each vertical line labelled (xj - xt) designates the absolute deviation of the mean of the set from the true value. In Figure 3.1, A represents (xj - xf) the absolute error obtained by analyst-1 for the assay of benzyl-iso-thioureahydrochloride, whereas B represents (x2 - x() the absolute error obtained by analyst-2 for the assay of the same compound. 

Figure 3.1 Absolute Errors in N Analysis by a Micro Kjeldahl s Method.

Example 3 Nitrogen containing compounds—They are estimated by micro Kjeldahl s Method. 

Nitrogenous Substances.—These are determined by Kjeldahl s method, as follows ... 

Hydrogen fluoride was identifled by vacuum distillation, formation of NaF.HF, and titration. Hydrogen chloride was identifled through formation of silver chloride. Ammonia was determined quantitatively by Kjeldahl s method. The oxynitrogen acids or oxychlorine acids were identified qualitatively by Lunge s reagent. Anions of the oxychlorine acids—i.e., chlorite, chlorate, or perchlorate— were identified by reduction with zinc to chloride ion. 

Kjeldahl flask. A round bottom flask with a long wide neck that is used in the determination of nitrogen by Kjeldahl s method. 

All protein determination methods described are not absolute and demand some form of calibration. The Kjeldahl s method remains the only official method currently available for calibration purposes and maintains its position as the most frequently used technique for the determination of organic nitrogen in food products. CE and immunochemical (enzyme-linked immunosorbent assay) techniques are most suitable for rapid separation and quantification of individual food proteins and are promising for widespread use in food protein analysis due to their high sensitivity, specificity, and simplicity of operation. There are numerous methods for the evaluation of the nutritional quality of food proteins. 

The mycelium was washed with Isotonic saline, resuspended In mineral salts medium with glucose (1% w/v) and mixed with a suspension of activated support. The mixture was stirred at 20 0 for 20 h and free mycelial forms were separated. The amount of bound dry weight per gram of carrier (the efficiency of Immobilization) was determined on the basis of nitrogen quantity by Kjeldahl s method. 

The total nitrogen is found by Kjeldahl s method, in which a known weight of material is boiled with concentrated sulphuric acid until all its nitrogen has been fixed as ammonium sulphate. Excess of sodium hydroxide is then added to liberate the ammonia, which is distilled over into a known volume of standard acid. From the amount of acid neutralised, the volume of liberated ammonia can be calculated and expressed in terms of nitrogen. 

Total nitrogen of the non-modified and modified seaweed polysaccharides and their blend was estimated by Kjeldahl s method [cf. 60], on a KEL PLUS-KES 20L Digestion unit attached to a KEL PLUS-CLASSIC DX Distillation unit (M/s PELICAN Equipments, Chennai, India). Crude protein content was calculated multiplying the nitrogen content by the factor 6.25 [cf. 60]. The results are the mean and standard deviation of 4 replicates. 

Kjeldahl s method A method used for the determination of nitrogen in organic compounds. The nitrogenous substance is converted to ammonium sulfate by boiling with concentrated sulfuric acid (often with a catalyst such as CUSO4) in a specially designed long-necked Kjeldahl flask. The mixture is then made alkaline and the ammonia distilled off into standard acid for measurement by titration. It is named for the Danish chemist Johan Kjeldahl (1849-1900). 

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