A: The UVabsorption spectrum of the Injection,diluted with 0.5Nsodium hydroxide to a concentration of about 8µg of anhydrous theophylline per mL,exhibits maxima and minima at the same wavelengths as that of a similar solution of USP Theophylline RS,concomitantly measured.

B: Add a few drops of the Injection to 5mLof hot alkaline cupric tartrate TS:a red to orange precipitate of cuprous oxide is formed.

Cation-exchange column— Proceed as directed under Column Partition Chromatography(see Chromatography á621ñ),using a chromatographic tube capable of providing a 0.8-×4-cm bed volume (or about 2mL)of 100-to 200-mesh,strongly acidic,styrene-divinylbenzene,cation-exchange resin.Condition the column by washing with about 30mLof water,discarding the eluate.

Procedure— Pass a volume of Injection containing about 100mg of hydrous dextrose through the resin bed in the Cation-exchange column,allowing the specimen to flow down the wall of the column so as not to disturb the resin bed,and collect the eluate in a 50-mLvolumetric flask.Wash the column with 25mLof water,and collect the eluate in the same 50-mLvolumetric flask.Dilute the eluate with water to volume,and mix to obtain the Test solution.In a similar manner,prepare a Reference solutionby passing 27mLof water through a freshly conditioned Cation-exchange column,collecting the eluate in a 50-mLvolumetric flask.Dilute with water to volume,and mix.Determine the absorbance of the Test solutionin a 1-cm cell at 284nm,with a suitable spectrophotometer,using the Reference solutionas the blank:the absorbance is not more than 0.25.

Buffer solution, Mobile phase,and Internal standard solution—Prepare as directed in the Assayunder Theophylline.

Standard preparation— Dissolve an accurately weighed quantity of USP Theophylline RSin Mobile phase,and dilute quantitatively,and stepwise if necessary,with Mobile phaseto obtain a solution having a known concentration of about 1mg per mL.Transfer 8.0mLof this solution to a 50-mLvolumetric flask,add 10.0mLof Internal standard solution,dilute with Mobile phaseto volume,and mix to obtain a solution having a known concentration of about 0.16mg of USP Theophylline RSper mL.

Assay preparation— Transfer an accurately measured volume of Injection,equivalent to about 16mg of theophylline,to a 100-mLvolumetric flask,add 20.0mLof Internal standard solution,dilute with Mobile phaseto volume,and mix.

Chromatographic system— Proceed as directed in the Assayunder Theophylline.

Procedure— Proceed as directed for Procedurein the Assayunder Theophylline.Calculate the quantity,in mg,of C7H8N4O2in each mLof the Injection taken by the formula: in which Vis the volume,in mL,of Injection taken,and the other terms are as defined therein.