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 Related compounds.

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 an accurately weighed quantity of USP Nimodipine RS to a suitable volumetric flask, dissolve in a volume of tetrahydrofuran equivalent to about 10% of the volume of the volumetric flask, and dilute with Mobile phase to volume to obtain a solution containing about 1.6 mg per mL. Dilute an aliquot of this solution with Mobile phase to obtain a solution having a known concentration of about 3.2 µg per mL.

Standard solution 2— Transfer accurately weighed quantities of USP Nimodipine RS and USP Nimodipine Related Compound A RS to a suitable volumetric flask, dissolve in a volume of tetrahydrofuran equivalent to about 10% of the volume of the volumetric flask, and dilute with Mobile phase to volume to obtain a solution containing 0.8 mg per mL each of USP Nimodipine RS and USP Nimodipine Related Compound A RS. Dilute an aliquot of this solution with Mobile phase to obtain a solution having a known concentration of about 1.6 µg per mL each of USP Nimodipine RS and USP Nimodipine Related Compound A RS.

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 2, and record the peak responses as directed for Procedure: 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%. [note—For the purpose of identification, the relative retention times are about 0.9 for nimodipine related compound A and 1.0 for nimodipine.]

Procedure— Separately inject equal volumes (about 20 µL) of Standard solution 1, Standard solution 2, 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 nimodipine related compound A in the portion of Nimodipine taken by the formula: in which CS is the concentration, in µg per mL, of USP Nimodipine Related Compound A RS in Standard solution 2; CT is the concentration, in mg per mL, of Nimodipine in the Test solution; and rU and rS are the peak responses of nimodipine related compound A obtained from the Test solution and Standard solution 2, respectively: not more than 0.1% of nimodipine related compound A is found. Calculate the percentage of any other impurity in the portion of Nimodipine taken by the formula: in which CS is the concentration, in µg per mL, of USP Nimodipine RS in Standard solution 1; CT is the concentration, in mg per mL, of Nimodipine in the Test solution; ri is the peak response of each impurity obtained from the Test solution; and rS is the peak response of nimodipine obtained from Standard solution 1: not more than 0.2% of any other impurity is found; and not more than 0.5% of total impurities is found.