Identification—
The UV absorption spectrum of the solution employed for measurement of absorbance in the
Assay exhibits maxima and minima at the same wavelengths as that of a similar solution of
USP Phenoxybenzamine Hydrochloride RS, concomitantly measured. The ratio
A268/
A272 of the maximum at 268 ± 2 nm and the minimum at 272 ± 2 nm is between 1.75 and 1.95.
Dissolution 
711
—
Medium:
0.1 N hydrochloric acid; 500 mL.
Apparatus 1:
100 rpm.
Time:
45 minutes.
Procedure—
Determine the amount of C
18H
22ClNO·HCl dissolved from UV absorbances at the wavelength of maximum absorbance at about 267 nm on 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 Phenoxybenzamine Hydrochloride RS in the same
Medium.
Tolerances—
Not less than 75% (Q) of the labeled amount of C18H22ClNO·HCl is dissolved in 45 minutes.
Assay—
Remove, as completely as possible, the contents of not fewer than 20 Capsules, and weigh. Transfer an accurately weighed portion of the mixed powder, equivalent to about 50 mg of phenoxybenzamine hydrochloride, to a 50-mL volumetric flask, add about 25 mL of a 1 in 1000 solution of hydrochloric acid in alcohol, and shake. Add the alcoholic hydrochloric acid to volume, mix, and filter, discarding the first 10 mL of the filtrate. Transfer 15.0 mL of the subsequent filtrate to a 100-mL volumetric flask, dilute with the alcoholic hydrochloric acid to volume, and mix. Concomitantly determine the absorbances of this solution and of a Standard solution of
USP Phenoxybenzamine Hydrochloride RS in the same medium having a known concentration of about 150 µg per mL in 1-cm cells at the wavelength of maximum absorbance at about 275 nm, with a suitable spectrophotometer, using a 1 in 1000 solution of hydrochloric acid in alcohol as the blank. Calculate the quantity, in mg, of C
18H
22ClNO·HCl in the portion of Capsules taken by the formula:
0.333C(AU / AS),
in which
C is the concentration, in µg per mL, of
USP Phenoxybenzamine Hydrochloride RS in the Standard solution, and
AU and
AS are the absorbances of the solution from the Capsules and the Standard solution, respectively.
