Ordinary impurities 
466
—
Test solution—
Prepare a solution in methanol having a known concentration of 2 mg per mL.
Standard solutions—
Prepare solutions in methanol having known concentrations of 2, 10, 20, and 40 µg per mL.
Eluant:
a mixture of butyl alcohol, glacial acetic acid, and water (5:3:2).
Visualization—
Expose the plate to chlorine gas for about 15 minutes, air-dry until the chlorine has dissipated (about 15 minutes), and follow with visualization technique 20.
Assay—
Transfer about 40 mg of Primidone, accurately weighed, to a 100-mL volumetric flask. Add 70 mL of alcohol, and boil gently to dissolve. Cool, and add alcohol to volume. Determine the absorbances in a 2-cm cell, with a suitable spectrophotometer, using alcohol as the blank, at the minima that occur at about 254 nm and 261 nm and at the maximum that occurs at about 257 nm. Concomitantly determine the absorbances of a Standard solution in alcohol of
USP Primidone RS, similarly prepared to have a known concentration of about 400 µg per mL. Calculate the quantity, in mg, of C
12H
14N
2O
2 in the Primidone taken by the formula:
0.1C(2A257 – A254 – A261)U / (2A257 – A254 – A261)S,
in which
C is the concentration, in µg per mL, of
USP Primidone RS in the Standard solution, and the parenthetic expressions are the differences in the absorbances of the two solutions at the wavelengths indicated by the subscripts for the solution of Primidone (
U) and the Standard solution (
S), respectively.
;)
for 2 hours: it loses not more than 0.5% of its weight.