Principles of Biochemistry (2+1)

Estimation of total nitrogen and protein content

Principle

• Nitrogen in the sample is converted into NH₄SO₄ by boiling with Conc.H₂SO₄ in the presence of a catalyst. 
• The digest is neutralized with alkali and the NH₄SO₄ is decomposed by heating with alkali (NaOH) and the liberated NH₃ is distilled and collected in a boric acid solution. 
• It is titrated against a very dilute H₂SO₄ and the N content is determined. 
• The protein content is then calculated by multiplying the N value with 6.25 (protein conversion factor).

                                          ∆                            ∆ Distilliation

Protein  + Conc. H₂SO₄    →   NH₄SO₄+NaOH  →  NH₃ ↑

                                      Catalyst