NOTE—Throughout the following procedures, protect test or assay specimens, the Reference Standards, and solutions containing them by conducting the procedures immediately under subdued light or using low-actinic glassware.

A: Infrared Absorption 197K.

B: The retention time of the major peak in the chromatogram of the Test solution corresponds to that in the chromatogram of Standard solution 1, as obtained in the test for Chromatographic purity.

Test solution: 50 mg per mL, in acetone.

Mobile phase— Prepare a filtered and degassed mixture of water, methanol, and tetrahydrofuran (3:1:1).

Standard solution 1— Transfer about 40 mg of USP Nimodipine RS, accurately weighed, to a 25-mL volumetric flask, dissolve in 2.5 mL of tetrahydrofuran, dilute with Mobile phase to volume, and mix. Transfer 1.0 mL of this solution to a 100-mL volumetric flask, dilute with Mobile phase to volume, and mix. Transfer 2.0 mL of this second solution to a 10-mL volumetric flask, dilute with Mobile phase to volume, and mix.

Standard solution 2— Transfer about 20.0 mg of USP Nimodipine Related Compound A RS, accurately weighed, to a 25-mL volumetric flask, dissolve in 2.5 mL of tetrahydrofuran, dilute with Mobile phase to volume, and mix. Transfer 5.0 mL of this solution to a 100-mL volumetric flask, dilute with Mobile phase to volume, and mix.

Standard solution 3— Transfer 2.5 mL of Standard solution 1 to a 100-mL volumetric flask, dilute with Mobile phase to volume, and mix.

Standard solution 4— Transfer 1.0 mL of Standard solution 2 and 1.0 mL of Standard solution 3 to a 25-mL volumetric flask, dilute with Mobile phase to volume, and mix.

Test solution— Transfer about 40 mg of Nimodipine, accurately weighed, to a 25-mL volumetric flask, dissolve in 2.5 mL of tetrahydrofuran, dilute with Mobile phase to volume, and mix.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 235-nm detector and a 4.6-mm × 12.5-cm column that contains packing L1. The flow rate is about 2 mL per minute. The column temperature is maintained at 40. Chromatograph Standard solution 4, and record the peak responses as directed for Procedure: the relative retention times are about 0.9 for nimodipine related compound A and 1.0 for nimodipine; the resolution, R, between nimodipine related compound A and nimodipine is not less than 1.5; and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 20 µL) of Standard solution 1, Standard solution 4, and the Test solution into the chromatograph, record the chromatograms, and measure the peak responses. [NOTE—Record the chromatogram of the Test solution for a period of time equivalent to four times the retention time of nimodipine.] Calculate the percentage of each impurity in the portion of Nimodipine taken by the formula: in which C is the concentration, in mg per mL, of USP Nimodipine Related Compound A RS in Standard solution 4; ri is the peak response of each impurity obtained from the Test solution; and rS is the peak response of nimodipine related compound A obtained from Standard solution 4: not more than 0.1% of nimodipine related compound A is found; not more than 0.2% of any other individual impurity is found; and not more than 0.5% of total impurities is found.

(Official January 1, 2007)