A:Infrared Absorption á197Kñ.

B: The retention time of the major peak in the chromatogram of the Test solutioncorresponds to that in the chromatogram of the Standard solution,as obtained in the test for Chromatographic purity.

pH7.5Phosphate buffer— Dissolve 2.7g of dibasic potassium phosphate in 800mLof water,add 2.4mLof triethylamine,adjust with phosphoric acid to a pHof about 7.5,and mix.

Mobile phase— Prepare a filtered and degassed mixture of pH7.5Phosphate bufferand acetonitrile (80:20).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard stock solution— Dissolve an accurately weighed quantity of USP Milrinone RSin Mobile phaseto obtain a solution having a known concentration of about 2mg per mL,heat in a water bath at approximately 80,and/or sonicate,if necessary.

Standard solution— Dilute an appropriate volume of Standard stock solutionquantitatively,and stepwise if necessary,with Mobile phaseto obtain a solution having a known concentration of 0.006mg per mL.

System suitability solution— Dissolve an accurately weighed quantity of USP Milrinone Related Compound A RSin Mobile phaseto obtain a solution having a known concentration of about 0.2mg per mL.Heat in a water bath at approximately 80,and/or sonicate,if necessary,to dissolve.Transfer 10.0mLof this solution and 1.0mLof the Standard stock solutionto a 100-mLvolumetric flask,dilute with Mobile phaseto volume,and mix.

Test solution— Transfer about 100mg of Milrinone,accurately weighed,to a 50-mLvolumetric flask,dissolve in and dilute with Mobile phaseto volume,and mix.Heat in a water bath at approximately 80,if necessary.

Chromatographic system (see Chromatography á621ñ)— The liquid chromatograph is equipped with a 220-nm detector and a 4.6-mm ×25-cm column that contains packing L7.The flow rate is about 1mLper minute.Chromatograph the System suitability solution,and record the peak responses as directed for Procedure:the relative retention times are about 0.6for milrinone related compound Aand 1.0for milrinone;the resolution,R,between milrinone related compound Aand milrinone is not less than 4.0;and the relative standard deviation for replicate injections of milrinone is not more than 5.0%.

Procedure— Separately inject equal volumes (about 20µL)of the Test solutionand the Standard solutioninto the chromatograph,record the chromatograms,and measure all the peak responses.Calculate the percentage of each impurity in the portion of Milrinone taken by the formula: in which Cis the concentration,in mg per mL,of USP Milrinone RSin the Standard solution;Wis the weight,in mg,of milrinone taken to prepare the Test solution;riis the peak response for each impurity obtained from the Test solution;and rSis the peak response obtained from the Standard solution:not more than 0.3%of any individual impurity is found;and not more than 1.0%of total impurities is found.

Solvent— Use dimethyl sulfoxide.