A: Infrared Absorption á197Mñ:previously dried at a pressure of not more than 5mm of mercury at 60for 3hours.

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.

Test solution: 10mg per mL,in water.

Phosphate buffer— Prepare a solution containing 0.01Mmonobasic sodium phosphate and 0.01Mdibasic sodium phosphate in a suitable container.Adjust with 0.1Msodium hydroxide or 0.1Mphosphoric acid to a pHof 7.0.

Solution A— Prepare a filtered and degassed mixture of Phosphate bufferand methanol (49:1).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).Prepare this solution fresh daily.

Solution B— Prepare a filtered and degassed mixture of Phosphate bufferand methanol (7:3).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).Prepare this solution fresh daily.

Mobile phase— Use variable mixtures of Solution Aand Solution Bas directed under Chromatographic system.

System suitability solution— Dissolve suitable quantities of uridine,USP Uracil Arabinoside RS,and USP Cytarabine RSin water to obtain a solution containing about 0.02,0.02,and 5.0mg per mL,respectively.

Standard solution— Dissolve an accurately weighed quantity of USP Cytarabine RSin water,and dilute quantitatively,and stepwise if necessary,with water to obtain a solution having a known concentration of about 4µg per mL.

Test solution— Transfer about 25mg of Cytarabine,accurately weighed,to a 5.0-mLvolumetric flask,dissolve in and dilute with water to volume,and mix.[NOTE—Prepare this solution fresh daily.]

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 254-nm detector and a 4.6-mm ×25-cm column that contains packing L1.The flow rate is about 1mLper minute.The chromatograph is programmed to provide variable mixtures of Solution Aand Solution B,the percentage of Solution Bbeing 0%at the time of injection.This composition is held for 10minutes.Solution Bis then linearly increased to 100%over a period of 10minutes.After maintaining this composition for 5minutes,the percentage of Solution Bis then linearly decreased to 0%over a period of 5minutes.This composition is maintained for 20minutes to equilibrate the system.Chromatograph the System suitability solution,and record the peak responses as directed under Procedure:the relative retention times are about 0.55for uracil,1.14for uridine,1.62for uracil arabinoside,and 1.0for cytarabine;and the resolution,R,between cytarabine and uridine is not less than 1.25.Chromatograph the Standard solution,and record the peak responses as directed under Procedure:the relative standard deviation for replicate injections is not more than 3.0%.

Procedure— Inject equal volumes (about 20µL)of the Standard solutionand the Test solutioninto the chromatograph,record the chromatograms,and measure the peak responses.Calculate the percentage of uracil arabinoside in the portion of Cytarabine taken by the formula: in which Cis the concentration,in mg per mL,of USP Cytarabine RSin the Standard solution;Wis the weight,in mg,of the specimen,1.34is the relative response factor for uracil arabinoside;riis the peak response of uracil arabinoside in the Test solution;and rSis the peak response of USP Cytarabine RSin the Standard solution:not more than 0.30%is found.

500(C/W)(ri/FrS),

Phosphate buffer— Dissolve 0.73g of monobasic sodium phosphate and 1.4g of dibasic sodium phosphate in 1liter of water,mix,and filter.

Mobile phase— Prepare a filtered and degassed mixture of Phosphate bufferand methanol (95:5).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard preparation— Dissolve an accurately weighed quantity of USP Cytarabine RSin water,and dilute quantitatively,and stepwise if necessary,with water to obtain a solution having a known concentration of about 0.1mg per mL.

Resolution solution— Dissolve an accurately weighed quantity of USP Uracil Arabinoside RSin Standard preparation,and dilute quantitatively,and stepwise if necessary,with Standard preparationto obtain a solution having a known concentration of about 0.1mg per mL.

Assay preparation— Transfer about 10mg of Cytarabine,accurately weighed,to a 100-mLvolumetric flask,dissolve in and dilute with water to volume,and mix.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 254-nm detector and a 4.6-mm ×25-cm column that contains packing L1.The flow rate is about 1.0mLper minute.Chromatograph the Resolution solution,and record the peak responses as directed for Procedure:the relative retention times are about 1.0for cytarabine and 1.3for uracil arabinoside;and the resolution,R,between cytarabine and uracil arabinoside is not less than 2.5.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the relative standard deviation for replicate injections is not more than 2.0%.[NOTE—After chromatography has been completed,flush the column with a mixture of water and methanol (7:3).]

Procedure— Separately inject equal volumes (about 10µL)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 C9H13N3O5in the portion of Cytarabine taken by the formula: in which Cis the concentration,in mg per mL,of USP Cytarabine RSin the Standard preparation;and rUand rSare the peak responses obtained from the Assay preparationand the Standard preparation,respectively.