Packaging and storage—
Preserve in tight, light-resistant containers.
pH 
791
:
between 4.8 and 6.0, in a solution (1 in 100).
Loss on drying 731—
Dry it in vacuum at 65
for 16 hours: it loses not more than 1.0% of its weight.
Selenium 291—
The absorbance of the solution from the
Test Solution, prepared with 100 mg of Methdilazine Hydrochloride and 100 mg of magnesium oxide, is not greater than one-half that from the
Standard Solution (0.003%).
Heavy metals, Method II 231:
0.002%.
Ordinary impurities 466—
Test solution:
methanol.
Standard solution:
methanol.
Application volume:
10 µL.
Eluant:
a mixture of toluene, isopropyl alcohol, and ammonium hydroxide (70:29:1), in a nonequilibrated chamber.
Visualization:
5.
Organic volatile impurities, Method I 467:
meets the requirements.
Assay—
Transfer about 100 mg of Methdilazine Hydrochloride, accurately weighed, to a 1000-mL volumetric flask, add water to volume, and mix. Transfer 5.0 mL of this solution to a 100-mL volumetric flask, dilute with water to volume, and mix. Concomitantly determine the absorbances of this solution and of a Standard solution of
USP Methdilazine Hydrochloride RS in the same medium having a known concentration of about 5 µg per mL, in 1-cm cells at 252 and 275 nm, with a suitable spectrophotometer, using water as the blank. Calculate the quantity, in mg, of C
18H
20N
2S·HCl in the portion of Methdilazine Hydrochloride taken by the formula:
20
C(
A252 
A275)
U / (
A252 A275)
S,
in which
C is the concentration, in µg per mL, of
USP Methdilazine Hydrochloride 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 Methdilazine Hydrochloride (
U) and the Standard solution (
S), respectively.
