Identification—
Transfer a portion of finely powdered Tablets, equivalent to about 10 mg of isoxsuprine hydrochloride, to a 60-mL beaker, add about 20 mL of water, mix, and filter. Transfer the clear filtrate to a 60-mL separator, add 10 mL of pH 9.0 alkaline borate buffer (see
Buffer Solutions in the section
Reagents, Indicators, and Solutions), and shake vigorously to mix. Extract with 2 mL of chloroform, filter the extract through a pledget of cotton, and mix the filtrate with 500 mg of potassium bromide. 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 isoxsuprine so obtained exhibits maxima only at the same wavelengths as that of a similar preparation of
USP Isoxsuprine Hydrochloride RS that has been treated in the same manner.
Dissolution 
711
—
Medium:
water; 900 mL.
Apparatus 1:
100 rpm.
Time:
45 minutes.
Procedure—
Determine the amount of C
18H
23NO
3·HCl dissolved from UV absorbances at the wavelength of maximum absorbance at about 269 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 Isoxsuprine Hydrochloride RS in the same medium.
Tolerances—
Not less than 75% (Q) of the labeled amount of C18H23NO3·HCl is dissolved in 45 minutes.
Assay—
Buffer solution—
Transfer about 1.32 g of anhydrous dibasic ammonium phosphate to a 1-liter volumetric flask, add about 950 mL of water, and mix. Adjust with phosphoric acid to a pH of 7.5, dilute with water to volume, and mix.
Mobile phase—
Prepare a filtered and degassed mixture of methanol and
Buffer solution (2:1). Make adjustments if necessary (see
System Suitability under
Chromatography 621).
Standard preparation—
Dissolve an accurately weighed quantity of
USP Isoxsuprine Hydrochloride RS in
Mobile phase, and dilute quantitatively, and stepwise if necessary, with
Mobile phase to obtain a solution having a known concentration of about 0.4 mg per mL.
Assay preparation—
Weigh and finely powder not fewer than 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 20 mg of isoxsuprine hydrochloride, to a 50-mL volumetric flask, and add about 25 mL of Mobile phase. Shake by mechanical means for 30 minutes, sonicate for ten minutes to dissolve, dilute with Mobile phase to volume, mix, and filter.
Chromatographic system
(see
Chromatography 621)—The liquid chromatograph is equipped with a 274-nm detector and a 3.9-mm × 30-cm column that contains packing L1. The flow rate is about 1.5 mL per minute. Chromatograph the
Standard preparation, and record the peak responses as directed for
Procedure: the column efficiency is not less than 1800 theoretical plates, and the relative standard deviation for replicate injections is not more than 2.0%.
Procedure—
Separately inject equal volumes (about 20 µL) of the
Standard preparation and the
Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of C
18H
23NO
3·HCl in the portion of Tablets taken by the formula:
50C(rU / rS),
in which
C is the concentration, in mg per mL, of
USP Isoxsuprine Hydrochloride RS in the
Standard preparation; and
rU and
rS are the peak responses obtained from the
Assay preparation and the
Standard preparation, respectively.
