A: Ultraviolet Absorption á197Uñ—

B: The retention time of the major peak in the chromatogram of the Assay preparationcorresponds 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 500mLof deaerated water into the dissolution vessel,adding 1.65mLof 30%lauryl dimethyl amine oxide,and mixing);500mL.

Apparatus 2: 50rpm.

Time: 45minutes.

Procedure— Determine the amount of C19H21N3O5dissolved by employing UVabsorption at the wavelength of maximum absorbance at about 328nm 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 RSin the same Medium.

Tolerances— Not less than 75%(Q)of the labeled amount of C19H21N3O5is dissolved in 45minutes.

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 RSin Mobile phase,with the aid of sonication if necessary,and dilute quantitatively,and stepwise if necessary,with Mobile phaseto obtain a solution having a known concentration of about 1µg per mL.[NOTE—If necessary,use 1mLof methanol per 20mLof Mobile phaseto dissolve the Reference Standard prior to diluting with Mobile phase.]

Test solution— Use the Assay preparation.

Procedure— Separately inject equal volumes (about 25µL)of the Standard solutionand the Test solutioninto 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 solutionis 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 Assayunder Isradipine.

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

Procedure— Separately inject equal volumes (about 25µL)of the Standard preparationand the Assay preparationinto 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 Cis the concentration,in mg per mL,of USP Isradipine RSin the Standard preparation;and rUand rSare the isradipine peak responses obtained from the Assay preparationand the Standard preparation,respectively.USP28