Test solution: 20mg per mL,in alcohol.

Mobile phase— Proceed as directed in the Assay.

Standard stock solution— Prepare as directed for Standard preparationin the Assay.

Standard solution— Transfer 1.0mLof the Standard stock solutionto a 50-mLvolumetric flask,dilute with Mobile phaseto volume,and mix.

Test solution— Prepare as directed for the Assay preparation.

Chromatographic system— Proceed as directed in the Assay.Chromatograph the Test solution,and record the peak responses as directed for Procedure:the resolution,R,between dinoprost tromethamine and any other adjacent peak is not less than 1.0.

Procedure— Separately inject equal volumes (about 10µL)of the Standard solutionand the Test solutioninto the chromatograph,record the chromatograms,and measure the peak responses.Calculate the percentage of each impurity in the portion of Dinoprost Tromethamine taken by the formula: in which Cis the concentration,in µg per mL,of USP Dinoprost Tromethamine RSin the Standard solution;Wis the weight,in mg,of Dinoprost Tromethamine taken to prepare the Test solution;Fis the relative response factor and is equal to 0.25for any peak at a relative retention time of about 0.30,1.7for any peak at a relative retention time of about 1.15,and 1.0for any other peak;riis the peak response of each impurity obtained from the Test solution;and rSis the peak response of dinoprost tromethamine obtained from the Standard solution:not more than 2.0%of any impurity having a relative retention time of about 0.94is found;not more than 1.5%of any impurity having a relative retention time of about 0.84is found;not more than 0.5%of any other impurity is found;and not more than 2.0%of all other impurities is found.

Mobile phase— Prepare a filtered and degassed mixture of water,acetonitrile,and phosphoric acid (750:250:1).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard preparation— Dissolve an accurately weighed quantity of USP Dinoprost Tromethamine RSin Mobile phase,and dilute quantitatively,and stepwise if necessary,with Mobile phaseto obtain a solution having a known concentration of about 1.0mg per mL.

Assay preparation— Transfer about 25.0mg of Dinoprost Tromethamine,accurately weighed,to a 25-mLvolumetric flask,dissolve in and dilute with Mobile phaseto volume,and mix.

Chromatographic system (see Chromatography á621ñ)— The liquid chromatograph is equipped with a 200-nm detector and a 3.9-mm ×15-cm column that contains packing L1.The flow rate is about 2mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the column efficiency is not less than 6000theoretical plates,and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 10µL)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 C20H34O5·C4H11NO3in the portion of Dinoprost Tromethamine taken by the formula: in which Cis the concentration,in mg per mL,of USP Dinoprost Tromethamine RSin the Standard preparation;and rUand rSare the peak responses obtained from the Assay preparationand the Standard preparation,respectively.