A: The UV absorption spectrum of the Injection, diluted with 0.5 N sodium hydroxide to a concentration of about 8 µg 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 5 mL of 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 621), using a chromatographic tube capable of providing a 0.8- × 4-cm bed volume (or about 2 mL) of 100- to 200-mesh, strongly acidic, styrene-divinylbenzene, cation-exchange resin. Condition the column by washing with about 30 mL of water, discarding the eluate.

Procedure— Pass a volume of Injection containing about 100 mg 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-mL volumetric flask. Wash the column with 25 mL of water, and collect the eluate in the same 50-mL volumetric flask. Dilute the eluate with water to volume, and mix to obtain the Test solution. In a similar manner, prepare a Reference solution by passing 27 mL of water through a freshly conditioned Cation-exchange column, collecting the eluate in a 50-mL volumetric flask. Dilute with water to volume, and mix. Determine the absorbance of the Test solution in a 1-cm cell at 284 nm, with a suitable spectrophotometer, using the Reference solution as the blank: the absorbance is not more than 0.25.

(Official January 1, 2007)

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

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

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

Chromatographic system— Proceed as directed in the Assay under Theophylline.

Procedure— Proceed as directed for Procedure in the Assay under Theophylline. Calculate the quantity, in mg, of C7H8N4O2 in each mL of the Injection taken by the formula: in which V is the volume, in mL, of Injection taken, and the other terms are as defined therein.

(100/52.9)(198.17/180.16)AR,