Chromatographic purity—
[NOTE—Use low-actinic glassware throughout this procedure, and otherwise protect the test specimen, the Reference Standard, and all solutions containing them from unnecessary exposure to light.
]
Mobile phase—
Prepare as directed in the
Assay.
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 with
Mobile phase to obtain a solution having a known concentration of about 6 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.
]
Resolution solution—
Use the
Standard preparation prepared as directed in the
Assay.
Test solution—
Transfer about 50 mg of Isradipine, accurately weighed, to a 25-mL volumetric flask, and add 5.0 mL of methanol to dissolve, using sonication if necessary. Dilute with Mobile phase to volume, and mix.
Chromatographic system
(see
Chromatography 
621
)—The liquid chromatograph is equipped with a 230-nm detector and a 4.6-mm × 10-cm column that contains packing L1. The flow rate is about 1.7 mL per minute. Chromatograph replicate injections of the
Resolution solution, and record the peak responses as directed under
Procedure: the resolution,
R, between isradipine and isradipine related compound A is not less than 1.5, and the relative standard deviation for replicate injections is not more than 1.5%.
Procedure—
Separately inject equal volumes (about 25 µL) of the Standard solution and the Test solution into the chromatograph, and allow the Test solution to elute for not less than three times the retention time of isradipine. Record the chromatograms, and measure the responses for all of the peaks: the sum of the peak responses, other than that of isradipine, in the chromatogram of the Test solution is not more than four times the isradipine response obtained from the Standard solution (1.2%), the response of the largest peak, other than that of isradipine, in the chromatogram of the Test solution is not more than 1.6 times greater than the isradipine response obtained from the Standard solution (0.5%), and no other peak response, other than that of isradipine, is greater than the isradipine response obtained from the Standard solution (0.3%).
Assay—
[NOTE—Use low-actinic glassware throughout this procedure, and otherwise protect the test specimen, the Reference Standard, and all solutions containing them, from unnecessary exposure to light.
]
Mobile phase—
Prepare a filtered and degassed mixture of water, methanol, and tetrahydrofuran (50:40:10). Make adjustments, if necessary (see
System Suitability under
Chromatography 621).
Standard preparation—
Dissolve, with the aid of sonication, if necessary, accurately weighed quantities of
USP Isradipine RS and
USP Isradipine Related Compound A RS in
Mobile phase, and dilute quantitatively, and stepwise, if necessary, with
Mobile phase to obtain a solution having known concentrations of 0.2 mg and 10 µg of
USP Isradipine RS and
USP Isradipine Related Compound A RS, respectively, per mL.
[NOTE—If necessary, 1 mL of methanol per 20 mL of
Mobile phase may be added to dissolve the Reference Standards.
]
Assay preparation—
Transfer about 20 mg of Isradipine, accurately weighed, to a 100-mL volumetric flask. Add sufficient methanol to dissolve, using sonication, if necessary. Dilute with Mobile phase to volume, and mix.
Chromatographic system
(see
Chromatography 621)—The liquid chromatograph is equipped with a 326-nm detector and a 4.6-mm × 10-cm column that contains packing L1. The flow rate is about 1.7 mL per minute. Chromatograph the
Standard preparation, and record the peak responses as directed for
Procedure: the resolution,
R, between isradipine and isradipine related compound A is not less than 1.5, and the relative standard deviation for replicate injections is not more than 1.5%.
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 C
19H
21N
3O
5 in the portion of Isradipine taken by the formula:
100C(rU / rS),
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.
;)
for 4 hours: it loses not more than 0.2% of its weight.