Page 64 - Feed Lab

Estimation of Crude Protein- Macro Kjeldhal Method Suguna Management System Ver 1.0 / SOP / FQL / P2 - 03 Page 2 of 3

250 ml of distilled water, AR grade

FNitrogen free concentrated sulphuric acid, AR
Grade.

BLANK
FTake 5gm activated sodium sulphate + 0.5gm of
cupric sulphate and 25 ml of concentrated
sulphuric acid to the Kjeldhal flask and do digestion
Picture-5 Picture-6
and distillation as per the crude protein procedure.
This is reagent blank. The reagent blank and direct
blank should be identical.

RECOVERY
FTake 0.1 gm of urea and add 5gm activated sodium
sulphate + 0.5gm of cupric sulphate and 25 ml of
concentrated sulphuric acid to the Kjeldhal flask
and do digestion and distillation as per the crude
protein procedure.
Picture-7 Picture-8
Calculation:
A = (28/60.06)x100
B = % of Nitrogen after distillation
Then (A/B) x 100 =recovery should
be 100+/- 1%

PROCEDURE
FTake accurately 2gm of ground sample on butter
paper. Fold the above sample and transfer to
Kjeldhal flask. (Picture-11)
Picture-9 Picture-10
FAdd 10gm activated sodium sulphate + 0.5gm of
cupric sulphate and 25 ml of concentrated
REAGENTS
F40% sodium hydroxide w/v, AR grade sulphuric acid to Kjeldhal flask. (Picture-12)

FSodium Sulphate , AR grade FDigest for 90 minutes to 105 minutes, till the
solution turns green/straw yellow colour. Cool the
FCupric Sulphate flask and add approximate 100 ml to 200 ml water.
Then shake well. (Picture-13)
F0.25 N sodium hydroxide (10.1g of sodium
hydroxide in one litre of water). FAfter cooling the flask, it is fitted to Kjeldhal
distillation apparatus and fit to all glassware's
F0.5 N sulphuric acid (14 ml of sulphuric acid in 1 litre
of water). properly without any leakage. (Picture-14)
FTake 20 ml of 0.5N sulphuric acid with 2 drops of
FMethyl red indicator.
methyl red indicator in the conical flask, which is
FPhenolphthalein indicator. receiver solution. (Picture-15)

F0.1 N Potassium Hydrogen Phthalate - 5.1055 g /

Prepared by : Approved by :
52 Director - Technical