Method for the estimation of Protein content

Method for the estimation of  Protein content

Reagents Required:

Potassium sulphate or anhydrous sodium sulphate.

Copper sulphate

Sulphuric acid --0.5N

      Sodium hydroxide pelletes

Distilled water

Zinc granulated

Apparatus Required:

Conical flask 250mL x 2

Beaker  - 250mL

Kjeldahl flask – 500mL

Procedure:

Weigh accurately about 1gm of sample in 500mL kjeldahl flask. Add 10gm of powdered K₂SO₄ or  anhydrous sodium sulphate (Na₂SO₄), 0.5gm of copper sulphate and 20mL Concentrated sulphuric Acid & incline the flask at an angle of about 45⁰C and gently  heat the mixture, keeping  below the boiling point of the mixture until forthing has ceased. Increase the heat until the acid boil and continue the heating until the solution has been clear green in color. Heat continuously for 4 hours.

Allow the mixture to cool add 150mL of water and  mix thoroughly the contents of the flask and cool again. Add 100mL of a 30% w/v solution of sodium hydroxide in water into flask. Add a few pieces of granulated zinc and connect the flask by  means of a kjeldahl connecting bulb with a condenser the delivery tube from which dips beneath the surface of a mixture of 50mL of 0.5N sulphuric acid, contained in a conical flask ( 250mL) and distill about 2/3 of the content of the flask have distilled over. Add about 3 drops of solution of methyl red to the content of the receiving flask and determine the excess of acid by titration with 0.5N NaOH.

The difference between the two titrations represent the acid required to neutralize the ammonia. Each mL of 0.5N sulphuric acid  is equivalent to 0.007004gm of Nitrogen

Calculation:

Percentage of Protein content (w/w) is calculated as :

(Blank titre – Sample titre)  X  0.007004  X Normality of  0.5N NaOH X 100x 6.25 

       

                                    Sample taken X 0.5