This document describes the Kjeldahl method for determining protein content using nitrogen analysis. The process involves digesting the sample using sulfuric acid and a catalyst to convert organic nitrogen into ammonium sulfate. The ammonia is then distilled and collected, followed by titration to determine the nitrogen content. The percentage of nitrogen is calculated using the titration results and sample weight. This nitrogen percentage can then be converted to a crude protein percentage by multiplying by 6.25. The method involves several steps - sample preparation, digestion to convert nitrogen, distillation to isolate ammonia, and titration to quantify the nitrogen.

1. BASIC
TRAINING:
DETERMINATIO
N OF PROTEIN
USING
KJELDAHL
METHOD

2. STEPS THROUGHOUT PROTEIN DETERMINATION
SAMPLE PREPARATION
•a) Grind dry the Soy
Beans to fineness grind
and do the Moisture
Analysis as per
FN/QAL/W07.
a.b) Mix liquids to
uniformity for the liquid
sample.
DIGESTION PROCESS
Organic nitrogen is
converted into
NH4+
DISTILLATION PROCESS
NH3 is distilled and
retained in a
receiver vessel.
TITRATION
Nitrogen is
determined.

3. ANALYTICAL PROCEDURE
DIGESTION PROCESS
i)1. Weigh 1 to 2 gram of samples into weighing
boat/small beaker and transfer into digestion flask.
i)2. Add 2 tablets of Kjeldahl Catalyst and 20mL of H2S04
Concentrated.
i)3. Place the digestion tube on the digestion block and placed the
suction module with the fitted gasket on the digestion tube.
Always remember to
conduct blank
sample

4. ANALYTICAL PROCEDURE
DIGESTION PROCESS
i)4. Digest the sample by setting the controller
at position 8~9 (approx. 470°C - 520°C) for ~90
minutes.
i)5. Let the digestion flask cool to room
temperature.
Thing to wonder:
Why need to
digest for 90
minutes?

5. ANALYTICAL PROCEDURE
DISTILLATION PROCESS
1. Add 50mL H2O into digestion tube
2. Connect the digestion flask to Distillation Unit and press “Reagent” to add 32% NaOH Solution.
i)3. Measure 60mL H3B03 4% into 500mL Erlenmeyer flask and 2 to 3 drops of Methyl Red/ Protein indicator.
What is the
purpose of
adding H2O?

6. ANALYTICAL PROCEDURE
DISTILLATION PROCESS
4. Place the (iii) Erlenmeyer flask at the distillate outlet and “On” the distillation unit.
5. Collect the distillate until ≥ 180mL.
i)6. Proceed for titration.
Ensure the tip
of distillate
outlet immerse
in Boric Acid.

7. ANALYTICAL PROCEDURE
TITRATION PROCESS
i)Fill the Burette
with H2SO4
0.25 mol/L.
i)Titrate the
distillate until
pH for receiver
end-point
changes
greenish to
pinkish.
i)Record the
volume of
the titrant.

8. CALCULATION:
 % Nitrogen = (ml-blank) x N x 1.401
Sample weight
 ml = sample titre
 blank = Blank titre
 N = Acid conc.
 % Protein (wet) = % Nitrogen X 6.25
 Conversion Factor (ƒ): refer to Food
 Regulation 1985 sub regulation 7
– crude protein 6.25