Mobile phase— Prepare a filtered and degassed mixture of 7mMammonium acetate and acetonitrile (1:1).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard preparation— Dissolve an accurately weighed quantity of USP Docusate Sodium RSin alcohol,and dilute quantitatively,and stepwise if necessary,with water to obtain a solution having a known concentration of about 1.0mg per mL.

System suitability solution— Transfer about 15mg of methylparaben,accurately weighed,to a 100-mLvolumetric flask,dissolve in and dilute with water to volume,and mix.Transfer 0.1mLof this solution to a suitable container,add 10mLof Standard preparation,and mix.

Assay preparation— Transfer 10Tablets to a 1-liter volumetric flask,add 200mLof alcohol and 300mLof water,and shake by mechanical means for not less than 90minutes to completely disintegrate the Tablets.Dilute with water to volume,mix,and filter,discarding the first 3mLof the filtrate.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 210-nm detector and a 4.6-mm ×10-cm column that contains packing L1.The flow rate is about 1mLper minute.The column temperature is maintained at 40.Chromatograph the System suitability solution,and record the peak responses as directed for Procedure:the relative retention times are about 0.74for methylparaben and 1.0for docusate,and the resolution,R,between methylparaben and docusate is not less than 2.0.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the tailing factor is not more than 2.5;and the relative standard deviation for replicate injections is not more than 1.8%.

Procedure— Separately inject equal volumes (about 40µL)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 C20H37NaO7Sin the portion of Tablets taken by the formula: in which Cis the concentration,in mg per mL,of USP Docusate Sodium RSin the Standard preparation;and rUand rSare the peak responses obtained from the Assay preparationand the Standard preparation,respectively.