note—Throughout the following procedures, protect test or assay specimens, the Reference Standard, and solutions containing them, by conducting the procedures without delay, under subdued light, or using low-actinic glassware.

Phosphate buffer— Transfer about 2.68 grams of dibasic sodium phosphate, heptahydrate to a 1-L volumetric flask, add 950 mL of water, and adjust to a pH of 3.0 with phosphoric acid, dilute to volume, and mix.

Mobile phase— Prepare a filtered and degassed mixture of acetonitrile and Phosphate buffer (7:3). Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparation— Dissolve an accurately weighed quantity of USP Prochlorperazine Maleate RS in Mobile phase, and dilute quantitatively, and stepwise if necessary, with Mobile phase to obtain a solution having a known concentration of prochlorperazine of about 0.1 mg per mL.

Assay preparation— Transfer an accurately measured portion of Injection, equivalent to about 10 mg of prochlorperazine, to a 100-mL volumetric flask, dissolve in Mobile phase, and dilute with Mobile phase to volume.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 254-nm detector and a 3.9-mm × 30-cm column that contains packing L1. The flow rate is about 1.5 mL per minute. The column temperature is maintained at 40. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the column efficiency is not less than 3000 theoretical plates, the tailing factor is not more than 2.5, and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 10 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 prochlorperazine (C20H24ClN3S) in the portion of Injection taken by the formula: in which 373.94 and 606.09 are the molecular weights of prochlorperazine and prochlorperazine maleate, respectively, C is the concentration, in mg per mL, of USP Prochlorperazine Maleate RS in the Standard preparation, and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.