Nitric acid diluent— Dilute 4 mL of nitric acid to 2000 mL with water.

Matrix modifier solution— Dissolve 1.5 g of magnesium nitrate in 1000 mL of water.

Standard stock solution— Proceed as directed in the chapter under Standard Preparations, beginning with “Treat some aluminum wire” and ending with “Cool, and transfer the solution, with the aid of water, to a 100-mL volumetric flask, dilute with water to volume, and mix.” Transfer 2 mL of this solution to a second 100-mL volumetric flask, dilute with water to volume, and mix. Transfer 2 mL of this solution to a third 100-mL volumetric flask, dilute with water to volume, and mix. This solution contains about 0.4 µg of aluminum per mL.

Standard solutions— Dilute accurately measured portions of the Standard stock solution with Nitric acid diluent to obtain solutions having known concentrations of about 2.5, 5.0, 10, 20, and 50 ng of aluminum per mL.

Test solution— Dilute 4.0 mL of Injection with 6.0 mL of Nitric acid diluent or use an appropriate dilution to obtain a solution having a concentration not greater than 0.02 µg of aluminum per mL.

System suitability solution— Dilute 9.5 mL of the Test solution with 0.5 mL of the Standard stock solution. If the resulting solution contains more than 0.04 µg of aluminum per mL, prepare an alternate dilution having a concentration between about 0.02 and 0.04 µg of aluminum per mL.

Procedure— Concomitantly determine the absorbances of the Standard solutions, the System suitability solution, and the Test solution at the aluminum emission line at 309.3 nm with a suitable atomic absorption spectrophotometer (see Spectrophotometry and Light-Scattering 851) equipped with an aluminum hollow-cathode lamp and a flameless electrically heated furnace. Under typical conditions, the sample volume is 20 µL, the volume of the Matrix modifier solution is 5 µL, the injection temperature is 100, and the oven conditions are as follows [note—These conditions may be optimized for each instrument]: Plot the absorbances of the Standard solutions versus the content of aluminum, in ng per mL, drawing a straight line best fitting the five points: the correlation coefficient is not less than 0.995; the recovery for the System suitability solution is between 80% and 120%; and the duplicate injections must agree within 0.0024 µg per mL. From the graph so obtained, determine the quantity of aluminum, C, in µg, found in each mL of the Test solution. Calculate the quantity, in µg, of aluminum in each mL of the Injection taken by the formula: in which C is as defined above; and D is the dilution factor used to prepare the Test solution: not more than 0.5 µg per mL is found.

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

Solution A— Prepare a filtered and degassed mixture of water and acetonitrile (85:15).

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— Prepare a solution of USP Paricalcitol Solution RS in Diluent having a known concentration of paricalcitol equal to about 0.5% of the labeled concentration of the Injection.

Control standard solution— Transfer 5.0 mL of the Standard solution to a 25.0-mL volumetric flask, dilute with Diluent to volume, and mix.

Degradation stock solution— Accurately dilute about 1 mL of USP Paricalcitol Solution RS with Diluent to 5 mL.

Degradation solution 1— Transfer about 1 mL of the Degradation stock solution and 0.1 mL of 30 percent hydrogen peroxide into a 10-mL container, and allow to stand at room temperature for 1 hour. Dilute with Diluent to 10 mL, and mix.

Degradation solution 2— Place about 1 mL of the Degradation stock solution and 1 mL of 0.1 N hydrochloric acid in a 10-mL container. Mix, and heat at 70 for 1 hour. Cool to room temperature, dilute with Diluent to 10 mL, and mix.

Test solution— Use the Injection.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 252-nm detector, a 4.6-mm × 7.5-cm guard column that contains packing L1, and a 4.6-mm × 25-cm column that contains 5-µm packing L1. The flow rate is about 1 mL per minute. The chromatograph is programmed as follows. 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 4.0 and 6.0; and the relative standard deviation for replicate injections of the Standard solution is not more than 5.0%.

Procedure— Chromatograph the Degradation solution 1, and identify the paricalcitol peak and the peaks due to the related compounds listed in Table 1. Chromatograph the Degradation solution 2, and identify the paricalcitol peak and the peaks due to the related compounds listed in Table 2. The resolution, R, between the paricalcitol peak and the related compound D peak is not less than 1.0. Separately inject equal volumes (about 100 to 200 µL) of the Diluent and the Test solution, in duplicate, 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 Injection taken by the formula: in which C is the concentration, in µg per mL, of paricalcitol in the Standard solution, calculated on the basis of the content of paricalcitol in the USP Paricalcitol Solution RS; L is the labeled amount, in µg per mL, of paricalcitol in the Injection; 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: in addition to not exceeding the limits for impurities in Tables 1 and 2, not more than 2.0% of total impurities is found.

Mobile phase— Prepare a filtered and degassed 0.01 N sulfuric acid solution.

Alcohol standard solution— Transfer 2.0 mL of dehydrated alcohol to a 10-mL volumetric flask, dilute with water to volume, and mix.

Propylene glycol standard solution— Transfer 3.0 mL of propylene glycol to a 10-mL volumetric flask, dilute with water to volume, and mix.

Standard solution— Transfer 5.0 mL each of Alcohol standard solution and Propylene glycol standard solution to a 50-mL volumetric flask, dilute with water to volume, and mix.

Test solution— Transfer 5.0 mL of the Injection to a 50-mL volumetric flask, dilute with water to volume, and mix.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a refractive index detector and a 7.8-mm × 30-cm column that contains packing L17. The column temperature is maintained at 60. The flow rate is about 0.8 mL per minute. Chromatograph the Standard solution, and record the peak responses as directed for Procedure: the elution order is propylene glycol followed by alcohol; the resolution, R, between propylene glycol and the alcohol is not less than 4.0; and the relative standard deviation for replicate injections is not more than 2.0% for each peak.

Procedure— Separately inject equal volumes (about 10 µL) of the Standard solution and the Test solution into the chromatograph, record the chromatographs, and measure the responses for the major peaks. Calculate the percentage of propylene glycol and alcohol in the portion of Injection taken by the formula: in which C is the concentration, in percentage, of alcohol or propylene glycol in the Alcohol standard solution or Propylene glycol standard solution, respectively; and rU and rS are the corresponding peak responses obtained from the Test solution and the Standard solution, respectively: between 16% and 24% of dehydrated alcohol is found; and between 26% and 34% of propylene glycol is found.

Diluent, Mobile phase, and Chromatographic system— Proceed as directed in the Assay under Paricalcitol.

Standard preparation— Prepare a solution of USP Paricalcitol Solution RS in Diluent having a known concentration of paricalcitol similar to that of the Injection.

Assay preparation— Use the Injection.

Procedure— Separately inject equal volumes (about 100 to 200 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 µg, of paricalcitol (C27H44O3) in each mL of the Injection taken by the formula: in which C is the concentration, in µg per mL, of paricalcitol in the Standard preparation, calculated on the basis of the content of paricalcitol in the USP Paricalcitol Solution RS; and rU and rS are the paricalcitol peak responses obtained from the Assay preparation and the Standard preparation, respectively.