SODIUM CHLORIDE—
Transfer an accurately weighed quantity of about 5 g of Low-Substituted Carboxymethylcellulose Sodium to a 250-mL conical flask, add 50 mL of water and 5 mL of 30% hydrogen peroxide, and heat on a water bath for 20 minutes, stirring occasionally to ensure hydration. Cool, add 100 mL of water and 10 mL of nitric acid, and titrate while stirring constantly with 0.05 N silver nitrate VS, determining the endpoint potentiometrically using a silver electrode and a mercurous sulfate electrode with a potassium sulfate bridge. Calculate the percentage of sodium chloride (NaCl) in the Low-Substituted Carboxymethylcellulose Sodium taken by the formula:
584.4VN/(100 – b)W,
in which 584.4 is the equivalence factor for sodium chloride;
V is the volume, in mL, of silver nitrate;
N is the normality of silver nitrate;
b is the percentage obtained from the test for
Loss on drying, determined separately; and
W is the weight, in g, of the Low-Substituted Carboxymethylcellulose Sodium taken.
SODIUM GLYCOLATE—
Test solution—
Transfer an accurately weighed quantity of about 500 mg of Low-Substituted Carboxymethylcellulose Sodium to a beaker, moisten thoroughly with 5 mL of glacial acetic acid, add 5 mL of water, and stir with a glass rod to ensure proper hydration (about 30 minutes). Add 80 mL of acetone while stirring, add 2 g of sodium chloride, and stir for several minutes to ensure the complete precipitation of carboxymethylcellulose. Pass through a fast filter paper, previously wetted with a small amount of acetone, and collect the filtrate in a 100-mL volumetric flask. Rinse the beaker and filter with acetone, and add the washings to the flask. Dilute the filtrate with acetone to volume, and mix. Allow to stand for 24 hours without shaking, and use the clear supernatant.
Standard stock solution—
Transfer 100 mg of glycolic acid, previously dried overnight in a vacuum desiccator over phosphorus pentoxide and accurately weighed, to a 100-mL volumetric flask, dissolve in and dilute with water to volume, and mix.
Standard solutions—
Into four identical 100-mL volumetric flasks, transfer 0.5-mL, 1.0-mL, 1.5-mL, and 2.0-mL portions of the Standard stock solution, respectively. To each flask, add water to make 5 mL, add 5 mL of glacial acetic acid, dilute with acetone to volume, and mix.
Blank—
Use an acetone solution containing 5% of glacial acetic acid and 5% water.
Procedure—
Transfer 2.0 mL of the
Test solution and 2.0 mL of each
Standard solution to separate 25-mL volumetric flasks. Place the uncovered flasks in a boiling water bath to remove the acetone, remove from the bath, and allow to cool. To each flask, add 5.0 mL of 2,7-dihydroxynaphthalene TS, mix, add an additional 15 mL of
2,7-dihydroxynaphthalene TS, and mix again. Cover the mouth of each flask with a small piece of aluminum foil, place the flasks upright in a boiling water bath for 20 minutes, remove from the bath, cool, dilute with sulfuric acid to volume, and mix. Determine the absorbance of each solution at 540 nm with a suitable spectrophotometer against the
Blank, and prepare a standard curve using the absorbances obtained from the
Standard solutions. From the standard curve and the absorbance of the
Test solution, determine the weight
(w), in mg, of glycolic acid in the
Test solution, and calculate the percentage of sodium glycolate in the Low-Substituted Carboxymethylcellulose Sodium taken by the formula:
(1.29)10w/[(100 – b)W],
in which 1.29 is a factor converting glycolic acid to sodium glycolate;
w is the weight, in mg, of glycolic acid from the standard curve;
b is the percentage obtained from the
Loss on drying test, determined separately; and
W is the weight, in g, of the Low-Substituted Carboxymethylcellulose Sodium taken. The sum of the percentages from the tests for
Sodium chloride and
Sodium glycolate is not more than 0.5%.
191
.
: it is between 6.5% and 13.5%, calculated on the dried basis.