A: Infrared Absorption 197K.

B: The retention time of the major peak in the chromatogram of the Assay preparation corresponds to that in the chromatogram of the Standard preparation, both relative to the internal standard, as obtained in the Assay.

Solvent— Use dimethyl sulfoxide.

(Official January 1, 2007)

Buffer solution— Transfer 2.72 g of sodium acetate trihydrate to a 2000-mL volumetric flask, add about 200 mL of water, and shake until dissolution is complete. Add 10.0 mL of glacial acetic acid, dilute with water to volume, and mix.

Mobile phase— Transfer 70.0 mL of acetonitrile to a 1000-mL volumetric flask, dilute with Buffer solution to volume, and mix. Degas, and filter before using. Make adjustments if necessary (see System Suitability under Chromatography 621).

Internal standard solution— Transfer about 50 mg of theobromine, accurately weighed, to a 100-mL volumetric flask, dissolve in 10.0 mL of 6 N ammonium hydroxide, dilute with Mobile phase to volume, and mix.

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 10.0 mL of this solution to a 100-mL volumetric flask, add 20.0 mL of Internal standard solution, dilute with Mobile phase to volume, and mix to obtain a solution having a known concentration of about 0.1 mg of USP Theophylline RS per mL.

Assay preparation— Transfer about 100 mg of Theophylline, accurately weighed, to a 100-mL volumetric flask, add about 50 mL of Mobile phase, shake by mechanical means until solution is complete, dilute with Mobile phase to volume, and mix. Transfer 10.0 mL of this solution to a second 100-mL volumetric flask, add 20.0 mL of Internal standard solution, dilute with Mobile phase to volume, and mix.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 280-nm detector and a 4-mm × 30-cm column that contains packing L1. The flow rate is about 1.0 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the resolution, R, between the theophylline and theobromine peaks is not less than 2.0, the tailing factor for the theophylline peak is not more than 2.0, and the relative standard deviation for replicate injections is not more than 1.5%.

Procedure— Separately inject equal volumes (between 10 µL and 25 µL) of the Standard preparation and the Assay preparation into the chromatograph, and measure the peak responses for the major peaks. The retention time of theophylline relative to that of theobromine is about 1.6. Calculate the quantity, in mg, of C7H8N4O2 in the portion of Theophylline taken by the formula: in which C is the concentration, in mg per mL, of USP Theophylline RS in the Standard preparation, and RU and RS are the response ratios of the theophylline peak to the internal standard peak obtained from the Assay preparation and the Standard preparation, respectively.