In this presentation I have mentioned whatever the possible relevant content is required for this method Citation Is done at the end of slide. Content is up to date & true to my belief. Thanks & Best Regards. Anurag Pandey B.Pharm (FACULTY OF PHARMACY, INVERTIS UNIVERSITY) M.Pharm (INSTITUTE OF PHARMACY, NIRMA UNIVERSITY) Email :- anurag.dmk05@gmail.com

1. NAME :- ANURAG PANDEY
COUSRE :- B.PHARM
YEAR :- 2ND YEAR (IVTH SEMSTER)
PRESENTED DATE :- 19-JANUARY-2015
PRESENTATION GIVEN BY :-
MR. SUNIL SINGH
(ASST. PROFESSOR
AT
INVERTIS INSTITUTE OF PHARMACY)

2.  INTRODUCTION
 THEORY
DIGESTION
DISTILLATION
TITRATION
 PROCEDURE
REAGENTS
MATERIAL AND EQUIPMENT
METHOD
 CYCLIC PROCESS OF THE PROCEDURE
 CALCULATION
 LIMITATION

3. Introduction
Kjeldahl's method is a faster method than Dumas' method. However, this method is used only for
those organic compounds that are converted quantitatively to ammonium sulphate on heating
strongly with concentrated sulphuric acid.
As the determination of the relative proportions (as percentage) of various elements present in an
organic compound is termed as quantitative analysis.
Theory :-
Kjeldahl's method involves three steps:
Digestion
A known mass (0.3 to 0.5 g) of the given organic compound is digested with concentrated H2SO4, in
presence of a small quantity of potassium sulphate and copper sulphate in a Kjeldahl's flask.
Potassium sulphate raises the boiling point of sulphuric acid and copper sulphate catalyzes the
digestion. In 3 to 4 hours, the organic compound is completely decomposed to form ammonium
sulphate.
Reaction :-
Distillation
The digested reaction mixture, on cooling, is transferred to a round bottomed distillation flask, and
distilled with a concentrated alkali solution (NaOH). Ammonia produced is absorbed in a known
volume of HCl solution of a known strength.
Reaction :-
Kjeldhal’s
method of
Nitrogen
estimation
1. Digestion 2. Distillation 3. Titration

4. The un-neutralised HCl is then back-titrated against a standard alkali. From the acid consumed, the
amount of ammonia produced and hence the mass of nitrogen is calculated.
Titration
Titration quantifies the amount of ammonia in the receiving solution. The amount of nitrogen in a
sample can be calculated from the quantified amount of ammonia ion in the receiving solution.
The are two types of titration :-
1. Back titration
2. Direct titration
Fig:16.17 Apparatus for the estimation of nitrogen by Kjeldahl's method
Procedure:-
Reagents :-
 Mercuric oxide, reagent grade.
 Potassium sulphate or anhydrous sodium sulphate, reagent grade.
 Sulphuric acid (98%), nitrogen free.
 Paraffin wax.
 40% solution of sodium hydroxide; dissolve 400 g of sodium hydroxide in water and dilute
to 1,000 ml.

5.  4% sodium sulphate solution.
 Boric acid indicator solution; add 5 ml of a solution with 0.1% methyl red and
 0.2% bromocresyl green to a saturated boric acid solution.
 Standard solution of 0.1N chlorhydric acid.
Material and equipment:-
 Kjeldahl digestion and distillation apparatus.
 500 ml Kjeldahl flasks.
 250 ml Erlenmeyer flasks.
 Glass beads.
Method
i. To milligram precision, weigh out 1 g of sample and place in the Kjeldahl flask; add 10g
potassium sulphate, 0.7 g mercuric oxide and 20 ml concentrated sulphuric acid.
ii. Place the flask tilted at an angle in the digester, bring to boiling point and retain until the
solution is clear; continue to heat 30 minutes more. If foam is too abundant, add a little
paraffin wax.
iii. Leave to cool, gradually adding approximately 90 ml distilled, de-ionized water. When
cold add 25 ml sodium sulphate solution and stir.
iv. Add one glass bead and 80 ml of 40% sodium hydroxide solution, keeping the flask tilted.
Two layers will form.
v. Quickly connect the flask to the distillation unit, heat and collect 50 ml of distillate
containing ammonia in 50 ml of indicator solution.
vi. At the end of distillation, remove the receptor flask, rinse the end of the condenser and
titrate the solution with the standard chlorhydric acid solution.
Cyclic process of the procedure

6. Figure:- Determination of Nitrogen by Kjeldahl's method.
Calculation :-
Let,
Mass of the organic compound = W g
Volume of the standard acid required for complete neutralization of the evolved ammonia = V mL
Normality of the standard solution of acid = N
From the law of equivalence (normality equation),
1000 mL of 1 N acid = 1000 mL of 1 N NH 3 = 17g NH 3 = 14 g nitrogen
Then,
V mL of N acid = V mL of NH 3
NV milli equivalent of acid = NV milli equivalent of ammonia
Therefore,
Then,
Percentage of nitrogen in the sample =
Or,
% of the nitrogen in the sample = 1.4 V*N
W
Where:
V = Acid used in titration (ml)
N = Normality of standard acid
W = Weight of sample (g)

7. Limitation
Kjeldahl's method cannot be used for the organic compounds :-
Containing nitrogen in the ring, e.g., pyridine, quinoline etc.
Containing nitro (-NO 2) and diazo (-N = N-) groups.