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

A: To 2 mL of Oral Solution add 3 mL of water and 3 or 4 drops of ferric chloride TS: a stable red color is produced.

B: To 1 mL of Oral Solution add 10 mL of bromine TS, previously warmed to room temperature: essentially no color change occurs (distinction from chlorpromazine hydrochloride, which immediately produces a green color).

for oral solution packaged in single-unit containers: meets the requirements.

for oral solution packaged in multiple-unit containers: meets the requirements.

Ion-pairing solution— Transfer 4.33 g of sodium 1-octanesulfonate, accurately weighed, to a 1-L volumetric flask. Dissolve in 500 mL of water, add 4.0 mL of glacial acetic acid, dilute with water to volume, and mix.

Mobile phase— Prepare a filtered and degassed mixture of Ion-pairing solution, acetonitrile, and methanol (50:40:10). Make adjustments if necessary (see System Suitability under Chromatography 621).

Diluting solution— Prepare a mixture containing 1000 mL of distilled water, 8.6 mL of concentrated hydrochloric acid, and 1000 mL of methanol.

Standard stock solution— Dissolve an accurately weighed quantity of USP Prochlorperazine Maleate RS in Diluting solution; and dilute quantitatively, and stepwise if necessary, with Diluting solution to obtain a solution having a known concentration of about 1.0 mg per mL.

Internal standard solution— Prepare a solution of trifluoperazine hydrochloride in Diluting solution containing about 0.9 mg per mL.

Standard preparation— Pipet 10.0 mL of the Standard stock solution and 10.0 mL of the Internal standard solution into a 100-mL volumetric flask. Dilute with Diluting solution to volume, and mix.

Assay preparation— Transfer a quantity of Oral Solution, equivalent to about 10.0 mg of prochlorperazine, to a 100-mL volumetric flask; add 10.0 mL of Internal standard solution; dilute with Diluting solution to volume; and mix.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 254-nm detector and a 3.9-mm × 15-cm column that contains 10-µm 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 relative retention times are about 1.3 for trifluoperazine and 1.0 for prochlorperazine; the resolution, R, between prochlorperazine and the internal standard is not less than 2.0; the tailing factor is not more than 2.0; 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 Oral Solution 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 ratios of the prochlorperazine peak to the internal standard peak obtained from the Assay preparation and the Standard preparation, respectively.