Assay
Mobile phase
Prepare a suitable filtered and degassed mixture of 0.01 M sodium acetate with a mixture of acetic acid having a concentration of 33 mL per L, acetonitrile, and 2-aminoheptane (50:50:0.5). Make adjustments if necessary (see
System Suitability under
Chromatography
621
).
Assay preparation
Agitate the container of Oral Suspension for 30 minutes on a rotating mixer, remove a 5-mL sample, store in a clear glass vial at 70

until analyzed. At time of analysis, remove the sample from the freezer, allow it to reach room temperature, and mix on a vortex mixer for 30 seconds. Pipet 1.0 mL of the sample solution into a 10-mL volumetric flask, and dilute with
Mobile phase to volume.
Chromatographic system (see Chromatography
621
)
The liquid chromatograph is equipped with a 278-nm detector and a 4.6-mm × 25-cm analytical column that contains 5-µm packing L1. The flow rate is about 0.5 mL per minute. Chromatograph the
Standard preparation, and record the peak responses as directed for
Procedure: the retention time for verapamil hydrochloride is about 4.8 minutes, and the relative standard deviation for replicate injections is not more than 0.7%.
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 verapamil hydrochloride (C
27H
38N
2O
4·HCl) in the volume of Oral Suspension taken by the formula:
100(C/V)(rU / rS)
in which
C is the concentration, in µg per mL, of
USP Verapamil Hydrochloride RS in the
Standard preparation; V is the volume, in mL, of Oral Suspension taken; and
rU and
rS are the peak responses obtained from the
Assay preparation and the
Standard preparation, respectively.
USP31