Principles of Biochemistry

Procedure

1. Preparation of the sample

• Weigh 0.5 g of dried sample into a Micro-kjeldahl digestion flask.
• Add 10ml of conc. H₂SO₄ and a pinch of digestion mixture and digest in a heating mantle till the solution becomes clear.
• Add a few drops of perchloric acid towards the end of the digestion and complete the digestion.
• Digest 5 ml of conc. H₂SO₄ and a pinch of the digestion mixture as blank.
• Cool the digested sample and blank and make up to 100 ml with distilled water in a volumetric flask separately.

2. Estimation

• Pipette out 5 ml of the above into the micro kjeldahl distillation chamber followed by 10 ml of 40% NaOH.
• Wash down the solution with 5 ml of distilled water and steam for 10 minutes.
• Collect the liberated NH₃ in a receiver flask containing 10 ml of 2% boric acid solution with a few drops of the indicator solution.
• Titrate the liberated NH₃ against 0.01N H₂SO₄.
• Calculate the N content and protein content in 100 g of the given sample.