Kjeldahl analysis

Kjeldahl analysis an acid-base titrimetric method for determining the amount of nitrogen in organic compounds, (p. 302)... 

Figure 10.7. Setup for performing Kjeldahl analysis of soil. On the left are two different types of Kjeldahl flask to the right of the flask is a heating block used to heat the test tube-shaped flask during digestion and on the right, a steam distillation unit.

A steam distillation apparatus is shown on the right-hand side of Figure 10.7. This same apparatus can be used to determine ammonia in soil as described previously. A flow diagram for the determination of ammonia in soil using a Kjeldahl analysis is given in Figure 10.8 [6],... 

Sulfuric acid h2so4 Commercially available concentrated solution is 96% (18 M) H2S04 a dense, syrupy liquid reacts on contact with skin and clothing evolves much heat when mixed with water Organic samples, such as for Kjeldahl analysis (see Chapter 5) also oxides of Al and Ti... 

The boiling point of ethyl phenylacetate is near that of benzyl cyanide. However, a Kjeldahl analysis of the product shows that only a trace of nitrogen compounds is present. 

In order to chemically analyse a sample of com for its protein content, a rather complex analytical procedure (e.g. Kjeldahl analysis) is required, a slow and expensive process. In our example, the PCR/PLS group of methods replaces this procedure with a much faster spectroscopic analysis. First, a mathematical relationship is established from a calibration set, comprising a matrix of NIR-spectra of the collection of samples and the vector of... 

Although this product cannot be purified by distillation, it contains almost the theoretical amount of nitrogen as shown by Kjeldahl analysis. 

Protein dispersibility index Dry product is dispersed in water by blending, then centrifuged at 880 x g for I0 min Protein dispersibility index (%) = (% water-dispersible prolein/% total protein) x 100 Advantages Tested in a collaborative study and found to be reproducible between laboratories. Disadvantages Limited to soy products protein is determined by Kjeldahl analysis, which can be a lengthy procedure. AOCS Method B a 10-65 (AOCS, 1999) AACC Method 46-24 (AACC, 2000)... 

These concentrations are determined by volumetric ammonia uptake measurements, Kjeldahl analysis and titrimetrical Cl analysis. The trichlorosilylation occurred at standard conditions and the ammoniation was performed for 5 h in excess ammonia. 

Kjeldahl analysis consists of adding various reagents to the sample in a glass tube, performing a digestion and developing a coloured complex whose concentration is determined spectrophotometrically. 

In papers dedicated to side reactions to nitration, no attention has been paid to the formation of ammonia in the course of the reaction. It is formed from hydrogen cyanide produced by drastic decomposition of nitro compounds. This was discussed in detail in Vol. I, pp. 76—77. The mechanism of the formation of HCN from C-nitro compounds also explains the fact that these nitro compounds yield ammonia in Kjeldahl analysis, where the substance is subjected to the action of oleum at high temperature. 

Fig. 12 gives an overview of the variables in the reactor model. In accordance with what was demonstrated by lacobucci et al. (18) it is assumed that the concentration of solubilized, permeable protein is equal on both sides of the membrane. This assumption is substantiated by the fact that the protein hydroly-zate consists mainly of smaller, soluble peptides and unconverted protein ( ). The concentration of accessible protein in the feed stream, SR, will be smaller than PR, as it is likely that a small, constant percentage of the protein is undegradable, in accordance with what was found by lacobucci et al. (18). This fraction counts as protein in a Kjeldahl analysis, but is otherwise consi-... 

---