A: Transfer a quantity of finely powdered Tablets, equivalent to about 10 mg of loperamide hydrochloride, to a test tube, add 20.0 mL of isopropyl alcohol, shake by mechanical means for 1 minute, and allow to settle. Pipet 9.0 mL of the supernatant into a 10-mL volumetric flask, and dilute with 0.1 N hydrochloric acid to volume. The solution so obtained meets the requirements for Identification test B under Loperamide Hydrochloride.

B: The retention time of the major peak in the chromatogram of the Assay preparation corresponds to that in the chromatogram of the Standard preparation, as obtained in the Assay.

Medium: 0.01 N hydrochloric acid; 900 mL.

Apparatus 2: 50 rpm.

Time: 30 minutes.

Mobile phase and Chromatographic system— Proceed as directed in the Assay.

Procedure— Separately inject equal volumes (about 50 µL) of a filtered portion of the solution under test into the chromatograph, record the chromatogram, and measure the response for the major peak. Calculate the quantity of C29H33ClN2O2·HCl dissolved in comparison with a Standard solution having a known concentration of USP Loperamide Hydrochloride RS in the same Medium and similarly chromatographed.

Tolerances— Not less than 80% (Q) of the labeled amount of C29H33ClN2O2·HCl is dissolved in 30 minutes.

(Official January 1, 2007)

Buffer solution— Transfer 3.0 g of triethylamine hydrochloride and 1.0 mL of phosphoric acid to a 1-L flask, add 550 mL of water, and mix.

Mobile phase— Prepare a filtered and degassed mixture of acetonitrile and Buffer solution (45:55). Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparation— Dissolve an accurately weighed quantity of USP Loperamide Hydrochloride RS in methanol to obtain a solution having a known concentration of about 2 mg per mL. Quantitatively dilute this solution with water to obtain a solution having a known concentration of about 0.2 mg per mL. Transfer 10.0 mL of this solution to a 250-mL volumetric flask, add 5.0 mL of 5% phosphoric acid solution and 25 mL of methanol, dilute with water to volume, and mix.

Assay preparation— Weigh and finely powder not fewer than 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 16 mg of loperamide hydrochloride, to a 2000-mL volumetric flask. Add 40 mL of 5% phosphoric acid solution and 200 mL of methanol, dilute with water to volume, and mix.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 214-nm detector and a 4-mm × 8-cm column that contains 5-µm packing L7. The flow rate is about 2 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: 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 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 loperamide hydrochloride (C29H33ClN2O2·HCl) in the portion of Tablets taken by the formula: in which C is the concentration, in mg per mL, of USP Loperamide Hydrochloride RS in the Standard preparation; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.