Limit of cyanide—
Dissolve 1.0 g in 10 mL of 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 develops within 15 minutes.
Chromatographic purity—
Mobile phase
and Chromatographic system—Proceed as directed in the Assay. To evaluate the system suitability requirements, use the Standard preparation as prepared in the Assay.
Standard solution—
Dissolve an accurately weighed quantity of
USP Methsuximide RS in
Mobile phase, and dilute quantitatively, and stepwise if necessary, with
Mobile phase to obtain a solution having a known concentration of about 6.0 µg per mL.
Test solution—
Transfer about 300 mg of Methsuximide, accurately weighed, to a 50-mL volumetric flask, dissolve in and dilute with Mobile phase to volume, and mix.
Procedure—
Separately inject equal volumes (about 20 µL) of the
Standard solution and the
Test solution into the chromatograph, record the chromatograms, and measure all of the peak responses. Calculate the percentage of each impurity in the portion of Methsuximide taken by the formula:
0.1(CS / CU)(ri / rS),
in which
CS is the concentration, in µg per mL, of
USP Methsuximide RS in the
Standard solution; CU is the concentration, in mg per mL, of Methsuximide in the
Test solution; ri is the peak response for each impurity obtained from the
Test solution; and
rS is the peak response for methsuximide obtained from the
Standard solution: not more than 0.1% of any individual impurity is found; and not more than 2.0% of total impurities is found.
Assay—
Mobile phase—
Prepare a filtered and degassed mixture of water and acetonitrile (11:9). Make adjustments if necessary (see
System Suitability under
Chromatography 
621
).
Standard preparation—
Dissolve an accurately weighed quantity of
USP Methsuximide RS in
Mobile phase, and dilute quantitatively, and stepwise if necessary, with
Mobile phase to obtain a solution having a known concentration of about 0.6 mg per mL.
Assay preparation—
Transfer about 120 mg of Methsuximide, accurately weighed, to a 200-mL volumetric flask, dissolve in and dilute with Mobile phase to volume, and mix.
Chromatographic system—
The liquid chromatograph is equipped with a 254-nm detector and a 3.9-mm × 30-cm column that contains packing L1. The flow rate is about 1 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the column efficiency is not less than 5800 theoretical plates; the tailing factor is not more than 1.3; and the relative standard deviation for replicate injections is not more than 0.6%.
Procedure—
Separately inject equal volumes (about 20 µL) of the
Standard preparation and the
Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of C
12H
13NO
2 in the portion of Methsuximide taken by the formula:
200CS(rU / rS),
in which
CS is the concentration, in mg per mL, of
USP Methsuximide RS in the
Standard preparation; and
rU and
rS are the peak responses obtained from the
Assay preparation and the
Standard preparation, respectively.
;)
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