Identification—
A:
Thin-Layer Chromatographic Identification Test 
201
—
Test solution—
Use the Injection.
Standard solution:
5 mg per mL in a mixture of methanol, water, and 0.1 N hydrochloric acid (5:4:1).
Developing solvent system:
a mixture of butyl alcohol, water, and glacial acetic acid (34:10:5).
Procedure—
Proceed as directed in the chapter. Locate the yellow spots on the plate: the RF value of the principal spot obtained from the Test solution corresponds to that of the principal spot obtained from the Standard solution. Spray the plate lightly with a spray reagent prepared as follows. Transfer 1 g of iodine and 3 g of potassium iodide to a 100-mL volumetric flask. Add 10 mL of alcohol to dissolve (heat gently). Add 20 mL of 2 N sulfuric acid, dilute with water to volume, and mix. Store in a dark place. Observe the plate, and locate the brown spots: the RF value of the principal spot obtained from the Test solution corresponds to that of the principal spot obtained from the Standard solution.
B:
The retention time of the major peak in the chromatogram of the Assay preparation corresponds to that in the chromatogram of the Standard preparation, as obtained in the Assay.
Chromatographic purity—
[NOTE—Protect dipyridamole solutions from exposure to light.
]
Mobile phase and Chromatographic system—
Proceed as directed in the Assay.
Test solution—
Use the Assay preparation prepared as directed in the Assay.
Procedure—
Inject a volume (about 10 µL) of the
Test solution into the chromatograph, record the chromatogram, and measure the peak responses. Calculate the percentage of each impurity in the portion of Injection taken by the formula:
100(ri / rs),
in which
ri is the peak response for each impurity; and
rs is the sum of the responses of all of the peaks: not more than 2.0% of any individual impurity is found; and not more than 4.5% of total impurities is found.
Assay—
[NOTE—Protect dipyridamole solutions from exposure to light.
]
Acetate buffer—
Dissolve a quantity of sodium acetate in water to obtain a concentration of about 6.8 mg per mL. Adjust with acetic acid to a pH of 5.1 ± 0.1.
Mobile phase—
Prepare a filtered and degassed mixture of methanol and
Acetate buffer (65:35). Make adjustments if necessary (see
System Suitability under
Chromatography 621).
Standard preparation—
Dissolve an accurately weighed quantity of
USP Dipyridamole RS in
Mobile phase, and dilute quantitatively, and stepwise if necessary, with
Mobile phase to obtain a solution having a known concentration of about 1.0 mg per mL.
Assay preparation—
Transfer an accurately measured volume of Injection, equivalent to about 25 mg of dipyridamole, to a 25-mL volumetric flask, dilute with Mobile phase to volume, and mix.
Chromatographic system (see Chromatography 621)—
The liquid chromatograph is equipped with a 276-nm detector and a 3.9-mm × 30-cm column that contains packing L1. The flow rate is about 1.0 mL per minute. Chromatograph the
Standard preparation, and record the peak responses as directed for
Procedure: the column efficiency is not less than 2000 theoretical plates; the tailing factor is not greater than 1.7; and the relative standard deviation for replicate injections is not greater than 2.0%.
Procedure—
Separately inject equal volumes (about 10 µL) of the
Standard preparation and the
Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of dipyridamole (C
24H
40N
8O
4) in the portion of Injection taken by the formula:
25C(rU / rS),
in which
C is the concentration, in mg per mL, of
USP Dipyridamole RS in the
Standard preparation; and
rU and
rS are the peak responses obtained from the
Assay preparation and the
Standard preparation, respectively.
