Identification—
A:
Dissolve about 500 mg in 10 mL of water in a separator, add 10 mL of 3 N hydrochloric acid, and extract the liberated thiopental with two 25-mL portions of chloroform. Evaporate the combined chloroform extracts to dryness. Add 10 mL of ether, evaporate again, and dry at 105
for 2 hours: the IR absorption spectrum of a potassium bromide dispersion of the residue so obtained exhibits maxima only at the same wavelengths as that of a similar preparation of
USP Thiopental RS.
B:
Ignite about 500 mg: the residue responds to the tests for
Sodium 
191
.
C:
Dissolve about 200 mg in 5 mL of 1 N sodium hydroxide, and add 2 mL of
lead acetate TS: a white precipitate is formed, and it gradually darkens when the mixture is boiled. Acidify the darkened mixture with hydrochloric acid: hydrogen sulfide is evolved, and it is recognizable by its darkening of moistened lead acetate test paper held in the vapor.
Ordinary impurities 466—
Test solution:
10 mg of Thiopental Sodium per mL of methanol.
Application volume:
40 µL.
Eluant:
a mixture of toluene and methanol (85:15).
Visualization:
1.
Assay—
Transfer about 100 mg of Thiopental Sodium, accurately weighed, to a 200-mL volumetric flask, add sodium hydroxide solution (1 in 250) to volume, and mix. Pipet 5 mL of the solution into a 500-mL volumetric flask, add sodium hydroxide solution (1 in 250) to volume, and mix. Dissolve an accurately weighed quantity of
USP Thiopental RS in sodium hydroxide solution (1 in 250), and dilute quantitatively and stepwise with sodium hydroxide solution (1 in 250) to obtain a Standard solution having a known concentration of about 5 µg per mL. Concomitantly determine the absorbances of both solutions in 1-cm cells at the wavelength of maximum absorbance at about 304 nm, with a suitable spectrophotometer, using sodium hydroxide solution (1 in 250) as the blank. Calculate the quantity, in mg, of C
11H
17N
2NaO
2S in the Thiopental Sodium taken by the formula:
20C(1.091AU / AS),
in which
C is the concentration, in µg per mL, of
USP Thiopental RS in the Standard solution, 1.091 is the ratio of the molecular weight of thiopental sodium to that of thiopental, and
AU and
AS are the absorbances of the solution of Thiopental Sodium and the Standard solution, respectively.
;)
