A: The retention time of the major peak in the chromatogram of the Assay preparationcorresponds to that in the chromatogram of the Standard preparation,as obtained in the Assay for diphenoxylate hydrochloride.

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

Medium: 0.2Macetic acid;500mL.

Apparatus 1: 150rpm.

Time: 45minutes.

Mobile phase— Prepare a suitable degassed mixture of acetonitrile and 0.05Mmonobasic potassium phosphate (65:35).

Standard solution— Dissolve an accurately weighed quantity of USP Diphenoxylate Hydrochloride RSin methanol to obtain a solution having a known concentration of about 250µg per mL.Pipet 10mLof this solution into a 500-mLvolumetric flask,dilute with Dissolution Mediumto volume,mix,and filter.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 210-nm detector and a 3.9-mm ×30-cm column that contains packing L11.The flow rate is about 1.0mLper minute.Chromatograph replicate injections of the Standard solution,and record the peak responses as directed for Procedure:the tailing factor is not more than 1.5;and the relative standard deviation is not more than 2.0%.

Procedure— Separately inject equal volumes (about 50µL)of the Standard solutionand of filtered portions of the solution under test into the chromatograph,record the chromatograms,measure the response for the major peak,and determine the amount of C30H32N2O2·HCl dissolved.

Tolerances— Not less than 75%(Q)of the labeled amount of C30H32N2O2·HCl is dissolved in 45minutes.

pH2.7Triethylamine phosphate buffer— Transfer approximately 18mLof triethylamine to a 2000-mLvolumetric flask containing about 1000mLof water,and mix.Add about 11.4mLof phosphoric acid,mix,and dilute with water to volume.

Mobile phase— Prepare a filtered and degassed mixture of acetonitrile and pH2.7Triethylamine phosphate buffer(55:45).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard preparation— Dissolve an accurately weighed quantity of USP Diphenoxylate Hydrochloride RSin Mobile phaseto obtain a solution having a known concentration of about 0.25mg per mL.

Assay preparation— Transfer an accurately counted number of Tablets,equivalent to about 25mg of diphenoxylate hydrochloride,to a 100-mLvolumetric flask,add Mobile phase,and shake by mechanical means for about 30minutes until the Tablets have disintegrated completely.Dilute with Mobile phaseto volume,and mix.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 254-nm detector and a 4.6-nm ×15-cm column that contains packing L7.The flow rate is about 1mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the relative standard deviation for diphenoxylate hydrochloride is not more than 2.0%.

Procedure— Separately inject equal volumes (about 25µL)of the Standard preparationand the Assay preparationinto 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 Tablets taken by the formula: in which Cis the concentration,in mg per mL,of USP Diphenoxylate Hydrochloride RSin the Standard preparation;Lis the labeled amount,in mg,of diphenoxylate hydrochloride in each Tablet;Dis the concentration,in mg per mL,of diphenoxylate hydrochloride in the Assay preparation;and rUand rSare the peak responses for diphenoxylate obtained from the Assay preparationand the Standard preparation,respectively.

pH2.7Triethylamine phosphate buffer— Prepare as directed in the Assay for diphenoxylate hydrochloride.

Mobile phase— Prepare a filtered and degassed mixture of pH2.7Triethylamine phosphate buffer,methanol,and acetonitrile (78:18:4).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard preparation— Dissolve an accurately weighed quantity of USP Atropine Sulfate RSin Mobile phase,and dilute quantitatively and stepwise with Mobile phaseto obtain a solution having a known concentration of about 5µg per mL.

Assay preparation— Transfer an accurately counted number of Tablets,equivalent to about 0.5mg of atropine sulfate,to a 100-mLvolumetric flask,add Mobile phase,and shake by mechanical means for about 30minutes until the Tablets have disintegrated completely.Dilute with Mobile phaseto volume,and mix.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 206-nm detector and a 4.6-mm ×15-cm column that contains packing L7.The flow rate is about 1mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the tailing factor for the atropine peak 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 25µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the quantity,in mg,of atropine sulfate [(C17H23NO3)2·H2SO4·H2O]in the portion of Tablets taken by the formula: in which 694.85and 676.83are the molecular weights of atropine sulfate monohydrate and anhydrous atropine sulfate,respectively;Cis the concentration,in µg per mL,of USP Atropine Sulfate RSin the Standard preparation;Lis the labeled amount,in mg,of atropine sulfate in each Tablet;Dis the concentration,in µg per mL,of atropine sulfate in the Assay preparation,based on the labeled quantity per Tablet and the extent of dilution;and rUand rSare the peak responses for atropine obtained from the Assay preparationand the Standard preparation,respectively.