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.

Medium: 0.01 N hydrochloric acid; 1000 mL.

Apparatus 1: 120 rpm.

Time: 30 minutes.

Procedure— Determine the amount of C22H29N3S2·2C4H4O4 dissolved by employing UV absorption at the wavelength of maximum absorbance at about 263 nm on filtered portions of the solution under test, suitably diluted with Dissolution Medium, if necessary, in comparison with a Standard solution having a known concentration of USP Thiethylperazine Maleate RS in the same Medium.

Tolerances— Not less than 75% (Q) of the labeled amount of C22H29N3S2·2C4H4O4 is dissolved in 30 minutes.

Mobile phase— Proceed as directed under the Assay for Thiethylperazine Maleate Suppositories.

Diluent— Prepare a mixture of acetonitrile and water (9:1).

Standard preparation— Dissolve an accurately weighed quantity of USP Thiethylperazine Maleate RS in Diluent by sonicating for about 5 minutes, and dilute quantitatively, and stepwise if necessary, with Diluent to obtain a solution having a known concentration of about 0.2 mg per mL.

Assay preparation— Weigh and finely powder not less than 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 50 mg of thiethylperazine maleate, to a 250-mL volumetric flask. Add 150 mL of Diluent, and shake to disperse the powder. Sonicate the mixture for 10 minutes, then shake by mechanical means for 1 hour. Dilute with Diluent to volume, and mix. Filter through a 0.45-µm filter, discarding the first portion of the filtrate.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 265-nm detector and a 4.6-mm × 25-cm column that contains 5-µm, base-deactivated packing L1. The flow rate is about 2 mL per minute, and the column temperature is maintained at 45. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the resolution, R, between the thiethylperazine peak and adjacent peaks is not less than 1.5, the column efficiency is not less than 1000 theoretical plates, the tailing factor for thiethylperazine 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 C22H29N3S2·2C4H4O4 in the portion of Tablets taken by the formula: in which C is the concentration, in mg per mL, of USP Thiethylperazine Maleate RS in the Standard preparation, and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.