for oral solution packaged in single-unit containers: meets the requirements with respect to diphenoxylate hydrochloride.

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

Solution A— Transfer 192 mg of sodium 1-pentanesulfonate monohydrate to a suitable container, add 200 mL of water, and sonicate to dissolve. Add 800 mL of water and 1.0 mL of phosphoric acid, and mix.

Solution B— Transfer 192 mg of sodium 1-pentanesulfonate monohydrate to a suitable container, add 200 mL of water, and sonicate to dissolve. Add 800 mL of acetonitrile, 1.0 mL of phosphoric acid, and mix.

Mobile phase— Prepare a filtered and degassed mixture of Solution B and Solution A (66:34). Make adjustments if necessary (see System Suitability under Chromatography 621).

Atropine stock preparation— Dissolve an accurately weighed quantity of USP Atropine Sulfate RS in dehydrated alcohol, and dilute quantitatively, and stepwise if necessary, with dehydrated alcohol to obtain a solution having a known concentration of about 0.04 mg per mL.

Standard preparation— Transfer about 20 mg of USP Diphenoxylate Hydrochloride RS to a 200-mL volumetric flask, add about 100 mL of dehydrated alcohol, and sonicate to dissolve. Accurately add 5.0 mL of Atropine stock preparation and 34 mL of water, and mix. Allow the solution to reach room temperature, and then dilute with dehydrated alcohol to volume. This solution contains about 0.1 mg of diphenoxylate hydrochloride and about 0.001 mg of atropine sulfate per mL.

Assay preparation— Transfer an accurately measured volume of the Oral Solution, equivalent to about 2.5 mg of diphenoxylate hydrochloride, based on the label claim, to a 25-mL volumetric flask, wash inside of the pipet with small portions of dehydrated alcohol, add the washings to the flask, dilute with dehydrated alcohol to volume, and mix. Pass a portion of the solution obtained through a 0.45-µm PTFE filter, discarding the first few mL, and use the clear filtrate.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 220-nm detector and a 4.6-mm × 25-cm column that contains 5-µm packing L10. The flow rate is about 1.7 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the relative retention times are about 0.35 for atropine and 1.0 for diphenoxylate; the resolution, R, between atropine and diphenoxylate is not less than 5.0; the tailing factor is not more than 1.5 for atropine; and the relative standard deviation for replicate injections is not more than 2.0% for diphenoxylate and not more than 5.0% for atropine. [note—If a significant tailing of the diphenoxylate peak is observed (greater than 2.5), it is recommended to maintain the column temperature at 25, to stabilize the system.]

Procedure— Separately inject equal volumes (about 50 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 diphenoxylate hydrochloride (C30H32N2O2·HCl) in the portion of Oral Solution taken by the formula: in which 25 is the volume, in mL, of the Assay preparation; CD is the concentration, in mg per mL, of USP Diphenoxylate Hydrochloride RS in the Standard preparation; and rU and rS are the diphenoxylate peak responses obtained from the Assay preparation and the Standard preparation, respectively.