A: Infrared Absorption 197K.

B: Ultraviolet Absorption 197U—

Diluent— Prepare a mixture of water and dehydrated alcohol (1:1).

Butylparaben solution— Transfer about 25 mg of butylparaben to a 100-mL volumetric flask, dilute with Diluent to volume, and mix

Solution A— Use filtered and degassed water.

Solution B— Use filtered and degassed acetonitrile.

Mobile phase— Use variable mixtures of Solution A and Solution B as directed for Chromatographic system. Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard solution— Dilute USP Paricalcitol Solution RS in Diluent to a known concentration of about 0.1 µg of paricalcitol per mL.

Control standard solution— Transfer 3.0 mL of the Standard solution to a 10.0-mL volumetric flask, dilute with Diluent to volume, and mix.

Test stock solution— Transfer about 10 mg of Paricalcitol, accurately weighed, to a 50-mL volumetric flask, dissolve in and dilute with dehydrated alcohol to volume, and mix.

Resolution solution— Transfer 1 mL of the Butylparaben solution and 1 mL of the Test stock solution to a 100-mL volumetric flask, dilute with Diluent to volume, and mix. Transfer 1 mL of this solution to a 10-mL volumetric flask, dilute with Diluent to volume, and mix.

Test solution— Prepare a mixture of the Test stock solution and water (1:1).

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 252-nm detector and a 4.6-mm × 25-cm column that contains 5-µm packing L1. The flow rate is about 2 mL per minute. The chromatograph is programmed as follows. Chromatograph the Resolution solution, and record the peak responses as directed for Procedure: the resolution, R, between paricalcitol and butylparaben is not less than 12.0. Chromatograph the Standard solution and the Control standard solution, and record the peak responses as directed for Procedure: the area ratio for the paricalcitol peak from the Standard solution to that from the Control standard solution is between 1.8 and 4.0; and the relative standard deviation for replicate injections of the Standard solution is not more than 10.0%.

Procedure— Separately inject equal volumes (about 100 µL) of the Diluent, the Standard solution, and the Test solution into the chromatograph, record the chromatograms, and measure the peak responses, disregarding any peaks corresponding to those obtained from the Diluent. Calculate the percentage of each impurity in the portion of Paricalcitol taken by the formula: in which C is the concentration, in µg per mL, of USP Paricalcitol RS in the Standard solution; W is the weight, in mg, of Paricalcitol taken to prepare the Test stock solution; ri is the peak response for each impurity obtained from the Test solution; and rS is the paricalcitol peak response obtained from the Standard solution: not more than 0.1% of any individual impurity is found; and not more than 0.5% of total impurities is found.

(Official January 1, 2007)

Mobile phase— Prepare a filtered and degassed mixture of methanol and water (4:1). Make adjustments if necessary (see System Suitability under Chromatography 621).

Diluent— Prepare a mixture of methanol and water (1:1).

Standard preparation— Prepare a solution of USP Paricalcitol RS in dehydrated alcohol having a known concentration of about 0.5 mg per mL. Dilute this solution quantitatively, and stepwise if necessary, with Diluent to obtain a solution having a known concentration of about 5.0 µg per mL.

Assay preparation— Transfer about 25 mg of Paricalcitol, accurately weighed, to a 50-mL low actinic volumetric flask, dissolve in and dilute with dehydrated alcohol to volume, and mix. Transfer 2.0 mL of this solution to a 200-mL volumetric flask, dilute with Diluent to volume, and mix.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 252-nm detector and a 4.6-mm × 25-cm column that contains 5-µm packing L1. The flow rate is about 2 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the tailing factor is not more than 2.0; and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 100 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 C27H44O3 in the portion of Paricalcitol taken by the formula: in which C is the concentration, in µg per mL, of USP Paricalcitol RS in the Standard preparation; and rU and rS are the paricalcitol peak responses obtained from the Assay preparation and the Standard preparation, respectively.