Nitric acid diluent— Dilute 4mLof nitric acid to 2000mLwith water.

Matrix modifier solution— Dissolve 1.5g of magnesium nitrate in 1000mLof 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-mLvolumetric flask,dilute with water to volume,and mix.”Transfer 2mLof this solution to a second 100-mLvolumetric flask,dilute with water to volume,and mix.Transfer 2mLof this solution to a third 100-mLvolumetric flask,dilute with water to volume,and mix.This solution contains about 0.4µg of aluminum per mL.

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

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

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

Procedure— Concomitantly determine the absorbances of the Standard solutions,the System suitability solution,and the Test solutionat the aluminum emission line at 309.3nm with a suitable atomic absorption spectrophotometer (see Spectrophotometry and Light-Scattering á851ñ)equipped with an aluminum hollow-cathode lamp and a flameless electrically heated furnace.Under typical conditions,the sample volume is 20µL,the volume of the Matrix modifier solutionis 5µL,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 solutionsversus 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 solutionis between 80%and 120%;and the duplicate injections must agree within 0.0024µg per mL.From the graph so obtained,determine the quantity of aluminum,C,in µg,found in each mLof the Test solution.Calculate the quantity,in µg,of aluminum in each mLof the Injection taken by the formula: in which Cis as defined above;and Dis the dilution factor used to prepare the Test solution:not more than 0.5µg per mLis 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 Aand Solution Bas directed for Chromatographic system.Make adjustments if necessary (see System Suitability underChromatography á621ñ).

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

Control standard solution— Transfer 5.0mLof the Standard solutionto a 25.0-mLvolumetric flask,dilute with Diluentto volume,and mix.

Degradation stock solution— Accurately dilute about 1mLof USP Paricalcitol Solution RSwith Diluentto 5mL.

Degradation solution 1— Transfer about 1mLof theDegradation stock solutionand 0.1mLof 30percent hydrogen peroxide into a 10-mLcontainer,and allow to stand at room temperature for 1hour.Dilute with Diluentto 10mL,and mix.

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

Test solution— Use the Injection.

Chromatographic system (see Chromatography á621ñ)— 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 1mLper minute.The chromatograph is programmed as follows. Chromatograph the Standard solutionand the Control standard solution,and record the peak responses as directed for Procedure:the area ratio for the paricalcitol peak from the Standard solutionto that from the Control standard solution is between 4.0and 6.0;and the relative standard deviation for replicate injections of the Standard solutionis 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 Dpeak is not less than 1.0. Separately inject equal volumes (about 100to 200µL)of the Diluentand 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 Cis 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;Lis the labeled amount,in µg per mL,of paricalcitol in the Injection;riis the peak response for each impurity obtained from the Test solution;and rSis the paricalcitol peak response obtained from the Standard solution:in addition to not exceeding the limits for impurities in Tables 1and 2,not more than 2.0%of total impurities is found.

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

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

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

Standard solution— Transfer 5.0mLeach of Alcohol standard solution and Propylene glycol standard solutionto a 50-mLvolumetric flask,dilute with water to volume,and mix.

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

Chromatographic system (see Chromatography á621ñ)— 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 0.8mLper 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 10µL)of the Standard solution and the Test solutioninto 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 Cis the concentration,in percentage,of alcohol or propylene glycol in the Alcohol standard solutionor Propylene glycol standard solution,respectively;and rUand rSare the corresponding peak responses obtained from the Test solutionand 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,andChromatographic system— Proceed as directed in the Assayunder Paricalcitol.

Standard preparation— Prepare a solution of USP Paricalcitol Solution RSin Diluenthaving a known concentration of paricalcitol similar to that of the Injection.

Assay preparation— Use the Injection.

Procedure— Separately inject equal volumes (about 100to 200µL)of the Standard preparationand 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 mLof the Injection taken by the formula: in which Cis 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 rUand rSare the paricalcitol peak responses obtained from the Assay preparation and the Standard preparation,respectively.