A: The contents of the Capsules respond to Identification tests A and B under Theophylline Tablets.

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, as obtained in the Assay.

Medium: water; 900 mL.

Apparatus 2: 50 rpm.

Time: 60 minutes.

Procedure— Determine the amount of C7H8N4O2 dissolved from UV absorbances at the wavelength of maximum absorbance at about 268 nm of filtered portions of the solution under test, suitably diluted with 0.1 N hydrochloric acid, if necessary, in comparison with a Standard solution having a known concentration of USP Theophylline RS in the same medium.

Tolerances— Not less than 80% (Q) of the labeled amount of C7H8N4O2 is dissolved in 60 minutes.

(Official January 1, 2007)

Mobile phase— Prepare a solution containing a mixture of water, methanol, and glacial acetic acid (64:35:1).

Standard preparation— Dissolve an accurately weighed quantity of USP Theophylline RS in methanol to obtain a solution having a known concentration of about 400 µg per mL.

Assay preparation for hard Capsules— Remove, as completely as possible, the contents of not less than 20 Capsules, weigh, and mix. Transfer an accurately weighed portion of the powder, equivalent to about 100 mg of anhydrous theophylline, to a 250-mL volumetric flask, add about 150 mL of methanol, and shake to dissolve. Dilute with methanol to volume, mix, and filter, using a membrane filter.

Assay preparation for soft Capsules— Cut open 20 Capsules, and place them in a 200-mL volumetric flask. Add 50 mL of 6 N ammonium hydroxide, shake to dissolve the contents, add water to volume, mix, and filter, discarding the first 20 mL of the filtrate. Transfer an accurately measured portion of the filtrate, equivalent to about 100 mg of anhydrous theophylline, to a 250-mL volumetric flask, add methanol to volume, mix, and filter through a membrane filter.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 254-nm detector and a 4-mm × 30-cm column that contains packing L1. The flow rate is about 2 mL per minute. Chromatograph three replicate injections of the Standard preparation, and record the peak responses as directed for Procedure: the relative standard deviation is not more than 2%.

Procedure— Separately inject equal volumes (about 20 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses. Calculate the quantity, in mg, of anhydrous theophylline in the portion of Capsule contents taken by the formula: in which C is the concentration, in µg per mL, of USP Theophylline RS in the Standard preparation, and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.