Chromatographic purity—
pH 7.5 Phosphate buffer—
Dissolve 2.7 g of dibasic potassium phosphate in 800 mL of water, add 2.4 mL of triethylamine, adjust with phosphoric acid to a pH of about 7.5, and mix.
Mobile phase—
Prepare a filtered and degassed mixture of
pH 7.5 Phosphate buffer and acetonitrile (80:20). Make adjustments if necessary (see
System Suitability under
Chromatography 
621
).
Standard stock solution—
Dissolve an accurately weighed quantity of
USP Milrinone RS in
Mobile phase to obtain a solution having a known concentration of about 2 mg per mL, heat in a water bath at approximately 80
, and/or sonicate, if necessary.
Standard solution—
Dilute an appropriate volume of Standard stock solution quantitatively, and stepwise if necessary, with Mobile phase to obtain a solution having a known concentration of 0.006 mg per mL.
System suitability solution—
Dissolve an accurately weighed quantity of
USP Milrinone Related Compound A RS in
Mobile phase to obtain a solution having a known concentration of about 0.2 mg per mL. Heat in a water bath at approximately 80
, and/or sonicate, if necessary, to dissolve. Transfer 10.0 mL of this solution and 1.0 mL of the
Standard stock solution to a 100-mL volumetric flask, dilute with
Mobile phase to volume, and mix.
Test solution—
Transfer about 100 mg of Milrinone, accurately weighed, to a 50-mL volumetric flask, dissolve in and dilute with
Mobile phase to volume, and mix. Heat in a water bath at approximately 80
, if necessary.
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 packing L7. The flow rate is about 1 mL per minute. Chromatograph the
System suitability solution, and record the peak responses as directed for
Procedure: the relative retention times are about 0.6 for milrinone related compound A and 1.0 for milrinone; the resolution,
R, between milrinone related compound A and 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 20 µL) of the
Test solution and the
Standard solution into 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:
5000(C/W)(ri / rS),
in which
C is the concentration, in mg per mL, of
USP Milrinone RS in the
Standard solution; W is the weight, in mg, of milrinone taken to prepare the
Test solution; ri is the peak response for each impurity obtained from the
Test solution; and
rS is 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.
;)
