kjeldhal method to determine the nitrogen content in food

Kjeldahl apparatus to determine the nitrogen content and presence of protein in food

1. Kjeldahl Method

2. Table of Contents Introduction Equipment and Apparatus The Process of  Kjeldahl Method Formula For Calculation Limitations of  Kjeldahl Method 2 Kjeldhal Method

3. Introduction The Kjeldahl method first came into existence in 1883 and was developed by a  Danish chemist named Johan Kjeldahl This method was specifically developed for  determining the nitrogen contents  in  organic substances 3 Kjeldhal Method

4. Equipment and Apparatus 4 Kjeldhal Method

5. The Process of  Kjeldahl Method T he Kjeldahl method is divided into three main steps The method has to be carried out in proper sequence The steps include digestion, distillation, and titration 5 Kjeldhal Method

6. D igestion In this method, a certain substance or sample is heated in the presence of sulphuric acid The acid breaks down the organic substance via oxidation and reduced nitrogen in the form of ammonium sulphate is liberated Potassium sulphate is usually added to increase the boiling point of the medium The sample is fully decomposed when we obtain a clear and colourless solution 6 Kjeldhal Method

7. 7 Kjeldhal Method

8. Distillation The distillation of the solution now takes place and a small quantity of sodium hydroxide is added to convert the ammonium salt to ammonia The distilled vapours are then trapped in a special trapping solution of HCl (hydrochloric acid) and water (NH4)2SO4+2NaOH→Na2SO4+2H2O+2NH3 8 Kjeldhal Method

9. Kjeldhal Method 9

10. Titration The amount of ammonia or the amount of nitrogen present in the sample is then determined by back titration As the ammonia dissolves in the acid trapping solution some HCl is neutralized. The acid that is left behind can be back titrated with a standard solution of a base such as NaOH or other bases. B(OH)2+H2O+Na2CO3→NaHCO3+CO2+H2O+NH3+HCl→NH4Cl 10 Kjeldhal Method

11. Formula For Calculation The percentage of nitrogen can be determined using the given formula: Percentage of nitrogen in the sample=1.4V∗NW Where, V = acid used in titration (ml) N = normality of standard acid W = weight of sample (g) 11 Kjeldhal Method

12. Advantages  Can be used in protein analysis of all foods. The operation is relatively simple. The experiment cost is low. The results are accurate and it is a classic method for protein determination. A modified method (micro  Kjeldahl  method) can be used to determine trace amounts of protein in the sample 12 Kjeldhal Method

13. Limitations of  Kjeldahl Method While the Kjeldahl method of nitrogen analysis has become the worldwide standard this method is not suitable for compounds containing nitrogen in azo and  nitro groups or in rings (quinoline, pyridine, etc.). In these cases, the nitrogen cannot be converted to ammonium sulphate by following the Kjeldahl method. 13 Kjeldhal Method

14. References https://byjus.com/chemistry/kjeldahl-method/ https://www.velp.com/en-ww/kjeldahl-method-1.aspx https://www.labconco.com/articles/a-brief-introduction-to-kjeldahl-nitrogen-determ https://pubs.acs.org/doi/10.1021/ed200863p 14 Kjeldhal Method