Limit of cyanide—
Dissolve 1.0 g in 10 mL of warm alcohol, and add 3 drops of
ferrous sulfate TS, 1 mL of 1 N sodium hydroxide, and a few drops of
ferric chloride TS. Warm gently, and finally acidify with 2 N sulfuric acid: no blue precipitate or blue color is formed within 15 minutes.
Ordinary impurities 
466
—
Test solution:
200 mg of phensuximide per mL in methylene chloride.
Standard solutions:
1.0, 2.0, and 4.0 mg per mL in methylene chloride.
Application volume:
5 µL.
Eluant:
a mixture of ethyl acetate and hexanes (1:1).
Visualization:
6.
Assay—
Transfer about 200 mg of Phensuximide, accurately weighed, to a 50-mL volumetric flask. Dissolve in 40 mL of alcohol, dilute with alcohol to volume, and mix. Transfer 5.0 mL of this solution to a 50-mL volumetric flask, dilute with alcohol to volume, and mix. Concomitantly determine the absorbances of this solution and of a Standard solution of
USP Phensuximide RS, in the same medium having a known concentration of about 400 µg per mL, in 1-cm cells at the wavelength of maximum absorbance at about 258 nm, with a suitable spectrophotometer, using alcohol as the blank. Calculate the quantity, in mg, of C
11H
11NO
2 in the Phensuximide taken by the formula:
0.5C(AU / AS),
in which
C is the concentration, in µg per mL, of
USP Phensuximide RS in the Standard solution, and
AU and
AS are the absorbances of the solution from Phensuximide and the Standard solution, respectively.
;)
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