A: Ultraviolet Absorption 197U—

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.

Medium: 0.1% aqueous solution of lauryl dimethyl amine oxide (prepared by transferring 500 mL of deaerated water into the dissolution vessel, adding 1.65 mL of 30% lauryl dimethyl amine oxide, and mixing); 500 mL.

Apparatus 2: 50 rpm.

Time: 45 minutes.

Procedure— Determine the amount of C19H21N3O5 dissolved by employing UV absorption at the wavelength of maximum absorbance at about 328 nm on filtered portions of the solution under test, suitably diluted with Medium, if necessary, in comparison with a Standard solution having a known concentration of USP Isradipine RS in the same Medium.

Tolerances— Not less than 75% (Q) of the labeled amount of C19H21N3O5 is dissolved in 45 minutes.

note—Isradipine is light sensitive. Throughout the following procedures, protect test or assay specimens, the Reference Standards, and solutions containing them from unnecessary exposure to light. Use low-actinic glassware, unless otherwise directed.

Mobile phase, Resolution solution, and Chromatographic system— Proceed as directed in the test for Chromatographic purity under Isradipine.

Standard solution— Dissolve an accurately weighed quantity of USP Isradipine RS in Mobile phase, with the aid of sonication if necessary, and dilute quantitatively, and stepwise if necessary, with Mobile phase to obtain a solution having a known concentration of about 1 µg per mL. [note—If necessary, use 1 mL of methanol per 20 mL of Mobile phase to dissolve the Reference Standard prior to diluting with Mobile phase.]

Test solution— Use the Assay preparation.

Procedure— Separately inject equal volumes (about 25 µL) of the Standard solution and the Test solution into the chromatograph, record the chromatograms, and measure the responses for all the peaks: the sum of all peak responses, other than that of isradipine, from the Test solution is not more than four times the isradipine response obtained from the Standard solution (2.0%); and no single peak response is greater than that of the isradipine peak response obtained from the Standard solution (0.5%).

Mobile phase, Standard preparation, and Chromatographic system— Proceed as directed in the Assay under Isradipine.

Assay preparation— Remove, as completely as possible, the contents of not fewer than 20 Capsules, and mix the combined contents. Transfer an accurately weighed quantity, equivalent to about 25 mg of isradipine, to a 100-mL volumetric flask. Add 5.0 mL of methanol and 5.0 mL of Mobile phase, and sonicate at room temperature for 15 minutes. Shake for 15 minutes in a mechanical shaker. Dilute with Mobile phase to volume, mix, and filter, discarding the first 5 mL of the filtrate.

Procedure— Separately inject equal volumes (about 25 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 isradipine (C19H21N3O5) in the portion of Capsules taken by the formula: in which C is the concentration, in mg per mL, of USP Isradipine RS in the Standard preparation; and rU and rS are the isradipine peak responses obtained from the Assay preparation and the Standard preparation, respectively.