Assay—
pH 7.5 Phosphate buffer—
Dissolve 8.71 g of dibasic potassium phosphate in about 800 mL of water, adjust with dilute phosphoric acid (1 in 10) to a pH of 7.5 ± 0.1, add water to make 1000 mL, and mix.
Mobile phase—
Prepare a filtered and degassed mixture of acetonitrile and
pH 7.5 Phosphate buffer (55:45). Make adjustments if necessary (see
System Suitability under
Chromatography 
621
).
Standard preparation—
Dissolve an accurately weighed quantity of
USP Pramoxine Hydrochloride RS in
Mobile phase to obtain a solution having a known concentration of about 0.5 mg per mL.
Assay preparation—
Transfer about 50 mg of Pramoxine Hydrochloride, accurately weighed, to a 100-mL volumetric flask, dissolve in and dilute with Mobile phase to volume, and mix.
Chromatographic system (see Chromatography 621)—
The liquid chromatograph is equipped with a 224-nm detector and a 4.6-mm × 25-cm column that contains packing L1. The column temperature is maintained at 40
, and the flow rate is about 2 mL per minute. Chromatograph the
Standard preparation, and record the peak responses as directed for
Procedure: the column efficiency is not less than 1500 theoretical plates; the tailing factor is not more than 1.5; and the relative standard deviation for replicate injections is not more than 1.5%.
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
17H
27NO
3· HCl in the portion of Pramoxine Hydrochloride taken by the formula:
100C(rU / rS),
in which
C is the concentration, in mg per mL, of
USP Pramoxine Hydrochloride RS in the
Standard preparation; and
rU and
rS are the peak responses obtained from the
Assay preparation and the
Standard preparation, respectively.
;)
