GENERAL TESTING PROCEDURE
TITLE: COLORIMETRIC SOLUTIONS (CS)
GTP No.
GTP020-00
Effective Date
Reference
USP
Page No.
1 of 4
1.0 PROCEDURE:
Cobaltous chloride CS (Red solution)
(Mol. Formula: CoCl2.6H2O, Mol. Wt: 237.93)
Reagents:
(1) Hydrogen peroxide TS: Pipette 10 mL of 30% hydrogen peroxide solution into a 100 mL volumetric
flask, dilute to volume with purified water.
(2) Sodium hydroxide solution (1 in 5) : Mix 10 g of sodium hydroxide with 50 mL of purified water.
(3) Dilute sulfuric acid (1 in 4) : Mix 10 mL of sulfuric acid with 40 mL of purified water.
(4) Hydrochloric acid and Purified water mixture (25 : 975) : Mix 25 mL of hydrochloric acid with 975
mL of purified water.
(5) Starch TS: Mix 1 g of soluble starch with 10 mg of red mercuric iodide and sufficient cold water to
make a thin paste. Add 200 mL of boiling water and boil for 1 minute with continuous stirring. Cool,
and use only the clear solution.
(6) 0.1N Sodium thiosulfate VS: Prepare and standardize as directed in the current version of General
Test Procedure: Preparation and Standardization of 0.1N Sodium Thiosulfate VS (GTP029).
Preparation: Transferred about 16.25 g of cobaltous chloride, accurately weighed to a 250 mL
volumetric flask, dissolved and diluted to volume with hydrochloric acid and purified water mixture (25:975).
Standardization:
(a) Pipette 5 mL of this solution into a 250 mL iodine flask, add 5 mL of hydrogen peroxide TS and 15 mL
of sodium hydroxide solution (1 in 5), boil for 10 minutes on a hot plate, cool and add 2 g of potassium
iodide and 20 mL of dilute sulfuric acid (1 in 4).
(b) When the precipitate has dissolved, add 3 mL of starch TS as the indicator, titrate the liberated iodine
with 0.1N sodium thiosulfate VS.
(c) Perform the blank determination with the same quantities of the same reagents.
GENERAL TESTING PROCEDURE
TITLE: COLORIMETRIC SOLUTIONS (CS)
GTP No.
GTP020-00
Effective Date
Reference
USP
Page No.
2 of 4
Calculations:
(V2 ~ V1) x N x 23.79
Contents of CoCl2. 6H2O = ------------------------------in mg per mL
0.1 x 5
Where,
V1 = Volume of 0.1N sodium thiosulfate consumed by the sample in mL,
V2 = Volume of 0.1N sodium thiosulfate consumed by the blank in mL,
N = Normality of 0.1N sodium thiosulfate VS.
Adjust the final volume of the solution by the addition of enough of the hydrochloric acid and purified water
mixture (25:975) so that each mL contains 59.5 mg of CoCl2. 6H2O.
Cupric sulfate CS
(Mol. formula: CuSO4.5H2O, Mol. Wt. :249.69)
Reagents:
(1) Hydrochloric acid and Purified water mixture (25 : 975) : Mix 25 mL of hydrochloric acid with 975
mL of purified water.
(2) Starch TS : Mix 1 g of soluble starch with 10 mg of red mercuric iodide and sufficient cold water to
make a thin paste. Add 200 mL of boiling water and boil for 1 minute with continuous stirring. Cool,
and use only the clear solution.
(3) 0.1N Sodium thiosulfate VS: Prepare and standardize as directed in the General Test Procedure;
Preparation and Standardization of 0.1N Sodium Thiosulfate VS.
Preparation : Transferred about 16.25g of Cupric sulphate, accurately weighed to a 250 mL
volumetric flask, dissolved and diluted to volume with hydrochloric acid and purified water mixture
(25:975)
Standardization :
GENERAL TESTING PROCEDURE
TITLE: COLORIMETRIC SOLUTIONS (CS)
GTP No.
GTP020-00
Effective Date
Reference
USP
Page No.
3 of 4
(a) Pipet 10 mL of this solution into a 250-mL iodine flask, add 40 mL of purified water, 4 mL of acetic acid,
3 g of potassium iodide and 5 mL of hydrochloric acid.
(b) Titrate the liberated iodine with 0.1N sodium thiosulfate VS by adding 3 mL of starch TS as indicator.
(c) Perform the blank determination with the same quantities of the same reagents.
Calculations :
(V2 ~ V1) x N x 24.97
Contents of CuSO4.5H2O = --------------------------------in mg per mL
0.1 x 10
Where,
V1 = Volume of 0.1N sodium thiosulfate consumed by the sample in mL,
V2 = Volume of 0.1N sodium thiosulfate consumed by the blank in mL,
N = Normality of 0.1N sodium thiosulfate VS.
Adjust the final volume of the solution by the addition of enough of the hydrochloric acid and purified water
mixture (25:975) so that each mL contains 62.4 mg of CuSO4.5H2O.
Ferric Chloride CS
(Mol. formula : FeCl3.6H2O, Mol. Wt. :270.3)
Reagents:
(1) Hydrochloric acid and Purified water mixture (25 : 975) : Mix 25 mL of hydrochloric acid with 975 mL
of purified water.
(2) Starch TS : Mix 1 g of soluble starch with 10 mg of red mercuric iodide and sufficient cold water to
make a thin paste. Add 200 mL of boiling water and boil for 1 minute with continuous stirring. Cool, and
use only the clear solution.
(3) 0.1N Sodium thiosulfate VS: Prepare and standardize as directed in the General Test Procedure;
Preparation and Standardization of 0.1N Sodium Thiosulfate VS.
Preparation: Transferred about 13.75g of ferric chloride, accurately weighed to 250 ml volumetric flask,
dissolve in 6.25 ml of HCl and dilute to volume with purified water.
GENERAL TESTING PROCEDURE
TITLE: COLORIMETRIC SOLUTIONS (CS)
GTP No.
GTP020-00
Effective Date
Reference
USP
Page No.
4 of 4
Standardization:
(a) Pipet 10 mL of this solution into a 250-mL iodine flask, add 15 mL of purified water, 3 g of potassium
iodide and 5 mL of hydrochloric acid, allow the mixture to stand for 15 minutes and add 100 mL of
purified water.
(b) Titrate the liberated iodine with 0.1N sodium thiosulfate VS by adding 3 mL of starch TS as indicator.
(c) Perform the blank determination with the same quantities of the same reagents.
Calculations:
(V2 ~ V1) x N x 27.03
Contents of FeCl3.6H2O = ----------------------------in mg per mL
10
Where,
V1 = Volume of 0.1N sodium thiosulfate consumed by the sample in mL,
V2 = Volume of 0.1N sodium thiosulfate consumed by the blank in mL,
N = Normality of 0.1N sodium thiosulfate VS.
Adjust the final volume of the solution by the addition of enough of the hydrochloric acid and purified water
mixture (25:975) so that each mL contains 45.0 mg of FeCl3.6H2O.