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.

A: Place a quantity of Suppositories, equivalent to about 5 mg of prochlorperazine, in a test tube, add 4 mL of dilute hydrochloric acid (1 in 2), warm on a steam bath to melt the solid, and swirl to mix: a pink color develops in the aqueous layer.

B: To the solution from Identification test A add 10 mL of bromine TS, and mix: essentially no color change occurs (distinction from chlorpromazine, which immediately produces a green color).

(Official January 1, 2007)

Standard preparation— Transfer about 40 mg of USP Prochlorperazine Maleate RS, accurately weighed, to a 250-mL separator containing 75 mL of ether. Add 0.5 mL of 6 N ammonium hydroxide, and proceed as directed for Assay preparation, beginning with “Extract with four 65-mL portions of dilute hydrochloric acid (1 in 100).”

Assay preparation— Weigh, mash, and then mix not less than 15 Suppositories. Transfer an accurately weighed quantity of the mass, equivalent to about 25 mg of prochlorperazine, to a 100-mL beaker. Dissolve in 50 mL of ether, and transfer to a 250-mL separator with the aid of three 25-mL portions of ether. Extract with four 65-mL portions of dilute hydrochloric acid (1 in 100), collecting the aqueous extracts in a 500-mL volumetric flask. Aerate the combined extracts for 15 to 20 minutes to remove dissolved ether. Add dilute hydrochloric acid (1 in 100) to volume, and mix. Filter a portion of the solution through filter paper, discarding the first 25 mL of the filtrate. To 25.0 mL of the subsequent filtrate add dilute hydrochloric acid (1 in 100) to make 200.0 mL, and mix.

Procedure— Concomitantly determine the absorbances of the Standard preparation and the Assay preparation in 1-cm cells at 254 nm and at 278 nm, with a suitable spectrophotometer, using dilute hydrochloric acid (1 in 100) as the blank. Calculate the quantity, in mg, of C20H24ClN3S in the portion of Suppositories taken by the formula: in which 0.617 is the ratio of the molecular weight of prochlorperazine to that of prochlorperazine maleate, W is the weight, in mg, of USP Prochlorperazine Maleate RS in the Standard preparation, and the parenthetic expressions are the differences in the absorbances of the two solutions at the wavelengths indicated by the subscripts, for the Assay preparation (U) and the Standard preparation (S), respectively.