Method
for the estimation of Tannin content
Reagent
Required:
Indigo carmine solution, Potassium
permanganate
Glass
wares and Apparatus Required:
1000mL conical flask, Burette and measuring
cylinder.
Procedure:
Weigh accurately about 0.10gm of sample and
dissolve it in 50mL of distilled water, add 750mL of distilled water and shake
well. Add 25mL indigo carmine solution. Shake well and titrate against N/10
KMnO4 up to golden yellow colour end point. Repeat the experiment with the same
quantity of reagents and in the same manner but omitting the substance. The
difference between the two titration represent the indigo carmine solution
required to neutralize the tannin. Each mL of 0.1N KMnO4 is
equivalent to 0.004157 gm of Tannin (as gallotannic acid).
Calculation:
Calculate the percentage of Tannin (as
gallotannic acid) (w/w) as :
(A – B) X 0.004157 X 100 x N
-------------------------------------------
W X 0.1
A =
Volume of 0.1N KMnO4 consumed in titration (Test)
B = Volume
of 0.1N KMnO4 consumed in titration (Blank)
W = Weight of material taken in gm
N =
Normality of Potassium permanganate
Reagent
Preparation:
Indigo
Carmine Solution:
Dissolve 1.5 gm Indigo carmine in 1000mL of
distilled water containing 50mL Sulphuric acid.
N/10
KMnO4 Solution :
Dissolve
about 3.3 gm KMnO4 in 1000mL of water, heat on a water bath for one hour
and allow to stand for two days and filter through whatman No.1 filter paper.
Standardize the solution as follows.
Standardize
the solution as follows:
Weigh accurately about 0.200 gm of sodium oxalate,
previously dried at 110oC, and dissolve it in 250mL of distilled water. Add 7mL
of sulphuric acid, heat to about 70oC and then slowly add the permanganate
solution from a burette, with constant shaking, until a pale pink colour which
persists for 15 seconds, is produced. The temperature should not be less than
60oC during titration. Calculate the normality of 0.1N KMnO4. Each 6.70 mg of sodium oxalate is equivalent
to 1mL of 0.1 N KMnO4.
For Raw
material :
Take 10mL of the filtrate from the estimation of water soluble extractive. Rest
the method is same as above.
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