Packaging and storage—
Preserve in tight containers.
Labeling—
Label it to indicate its viscosity and its nominal phthalyl content.
Viscosity 
911
—
Dissolve 10 g, previously dried at 105
for 1 hour, in 90 g of a mixture of equal weights of methanol and methylene chloride by mixing and shaking: the viscosity, determined at 20 ± 0.1
(see
Procedure for Cellulose Derivatives under
Viscosity 911), is not less than 80% and not more than 120% of that indicated by the label.
Chloride 221—
Dissolve 1.0 g in 40 mL of 0.2 N sodium hydroxide, add 1 drop of phenolphthalein TS, and add 2 N nitric acid dropwise, with stirring, until the red color is discharged. Add an additional 20 mL of 2 N nitric acid with stirring. Heat on a water bath, with stirring, until the gel-like precipitate formed becomes granular. Cool the mixture, and centrifuge. Separate the liquid phase, and wash the residue with three successive 20-mL portions of water, separating the washings by centrifuging. Dilute the combined liquids with water to 200 mL, mix, and filter. A 50-mL portion of the filtrate so obtained shows no more chloride than a control solution made by treating 0.50 mL of 0.01 N hydrochloric acid with 10 mL of 0.2 N sodium hydroxide, adding 7 mL of 2 N nitric acid, and diluting with water to 50 mL (0.07%).
Limit of free phthalic acid—
Mobile phase—
Prepare a filtered and degassed mixture of 0.1 M cyanoacetic acid and acetonitrile (85:15). Make adjustments if necessary (see
System Suitability under
Chromatography 621).
Standard solution—
Transfer about 12.5 mg of phthalic acid, accurately weighed, to a 250-mL volumetric flask, add about 125 mL of acetonitrile, and mix to dissolve. Add 25 mL of water, dilute with acetonitrile to volume, and mix.
Test solution—
Transfer about 200 mg of Hypromellose Phthalate, accurately weighed, to a 100-mL volumetric flask, add about 50 mL of acetonitrile, and sonicate to dissolve partially. Add 10 mL of water, and sonicate to dissolve. Cool to room temperature, dilute with acetonitrile to volume, and mix.
Chromatographic system—
The liquid chromatograph is equipped with a 235-nm detector and a 4.6-mm × 25-cm column that contains packing L1 with a high carbon load. The flow rate is about 2.0 mL per minute. Chromatograph the Standard solution, and record the peak responses as directed for Procedure: the relative standard deviation for replicate injections is not more than 1.0%.
Procedure—
Separately inject equal volumes (about 10 µL) of the
Standard solution and the
Test solution into the chromatograph, record the chromatograms, and measure the peak responses. Calculate the percentage of phthalic acid in the portion of Hypromellose Phthalate taken by the formula:
10(C / W)(rU / rS),
in which
C is the concentration, in µg per mL, of phthalic acid in the
Standard solution; W is the weight, in mg, on the anhydrous basis, of Hypromellose Phthalate taken to prepare the
Test solution; and
rU and
rS are the phthalic acid peak responses obtained from the
Test solution and the
Standard solution, respectively: not more than 1.0% is found.
Phthalyl content—
Transfer about 1 g, accurately weighed, to a conical flask, dissolve in 50 mL of a mixture of alcohol, acetone, and water (2:2:1), add
phenolphthalein TS, and titrate with 0.1 N sodium hydroxide VS. Perform a blank determination, and make any necessary correction. Calculate the percentage of phthalyl taken by the formula:
0.01(149.1)(
V/
W)
2(149.1/166.1)(
P),
in which 149.1 and 166.1 are the molecular weights of the phthalyl group and phthalic acid, respectively;
V is the volume, in mL, of 0.1 N sodium hydroxide consumed after correction for the blank;
W is the weight, in g, calculated on the anhydrous basis, of Hypromellose Phthalate taken; and
P is the percentage of free phthalic acid found as directed in the test for
Limit of free phthalic acid.
