Identification—
Transfer a portion of finely powdered Tablets, equivalent to about 8 mg of methdilazine hydrochloride, to a 60-mL separator, add 10 mL of sodium bicarbonate solution (1 in 10), and extract with 3 mL of chloroform. Filter the extract through a pledget of cotton. Evaporate the chloroform, carefully removing the last trace of solvent in a small vacuum flask: the IR absorption spectrum of a potassium bromide dispersion of the methdilazine so obtained exhibits maxima only at the same wavelengths as that of a similar preparation of
USP Methdilazine Hydrochloride RS, similarly treated and measured.
Dissolution 
711
—
Medium:
water; 900 mL.
Apparatus 1:
100 rpm.
Time:
45 minutes.
Procedure—
Determine the amount of C
18H
20N
2S·HCl dissolved from UV absorbances at the wavelength of maximum absorbance at about 252 nm of filtered portions of the solution under test, suitably diluted with
Dissolution Medium, if necessary, in comparison with a Standard solution having a known concentration of
USP Methdilazine Hydrochloride RS in the same
Medium.
Tolerances—
Not less than 75% (Q) of the labeled amount of C18H20N2S·HCl is dissolved in 45 minutes.
Assay—
Standard preparation—
Dissolve a suitable quantity of
USP Methdilazine Hydrochloride RS, accurately weighed, in chloroform, and dilute quantitatively with chloroform to obtain a solution having a known concentration of about 400 µg per mL.
Assay preparation—
Weigh and finely powder not fewer than 20 Tablets, and transfer an accurately weighed portion of the powder, equivalent to about 80 mg of methdilazine hydrochloride, to a 200-mL volumetric flask. Add 60 mL of chloroform, shake for 20 minutes, dilute with chloroform to volume, and mix. Filter, discarding the first 15 mL of the filtrate. Use the subsequent filtrate as directed in the Procedure.
Procedure—
Into three separate 100-mL volumetric flasks transfer 10.0 mL each of the
Standard preparation, the
Assay preparation, and chloroform to provide the blank. To each flask add 20 mL of chloroform and 4.0 mL of buffered palladium chloride TS, dilute with alcohol to volume, and mix. Concomitantly determine the absorbances of the solutions in 1-cm cells at the wavelength of maximum absorbance at about 460 nm, with a suitable spectrophotometer, using the blank to set the instrument. Calculate the quantity, in mg, of methdilazine hydrochloride (C
18H
20N
2S·HCl) in the portion of Tablets taken by the formula:
0.2C(AU / AS),
in which
C is the concentration, in µg per mL, of
USP Methdilazine Hydrochloride RS in the
Standard preparation; and
AU and
AS are the absorbances of the solutions from the
Assay preparation and the
Standard preparation, respectively.
