Identification—
The chromatogram of the
Assay preparation obtained as directed in the
Assay exhibits a major peak for theophylline, the retention time of which corresponds to that exhibited in the chromatogram of the
Standard preparation obtained as directed in the
Assay.
Dissolution 
711
—
Medium:
water; 900 mL.
Apparatus 2:
50 rpm.
Time:
30 minutes.
Procedure—
Determine the amount of C
7H
8N
4O
2 dissolved from UV absorbances at the wavelength of maximum absorbance at about 270 nm of filtered portions of the solution under test, suitably diluted with water, if necessary, in comparison with a Standard solution having a known concentration of
USP Oxtriphylline RS in the same medium.
Tolerances—
Not less than 80% (Q) of the labeled amount of C7H8N4O2 is dissolved in 30 minutes.
Assay—
Mobile phase—
Dissolve 6.8 g of monobasic potassium phosphate in water to make 1000 mL, and adjust with 0.1 N potassium hydroxide to a pH of 5.8 ± 0.1. Prepare a filtered and degassed mixture of this solution and methanol (4:1). Make adjustments if necessary (see
System Suitability under
Chromatography 621).
System suitability preparation—
Dissolve suitable quantities of
USP Oxtriphylline RS and theobromine in water to obtain a solution containing about 0.6 mg and 0.3 mg per mL, respectively. Dilute this solution quantitatively, and stepwise if necessary, with water to obtain a solution containing about 60 µg of
USP Oxtriphylline RS per mL and about 30 µg of theobromine per mL.
Standard preparation—
Dissolve an accurately weighed quantity of
USP Oxtriphylline RS in water, and dilute quantitatively, and stepwise if necessary, with water to obtain a solution having a known concentration of about 0.1 mg per mL.
Assay preparation—
Place 10 Tablets in a 1000-mL volumetric flask, and add about 700 mL of water. Heat on a steam bath, with occasional shaking, until the Tablets have disintegrated. Cool to room temperature, dilute with water to volume, mix, and filter. Transfer an accurately measured volume of this solution, equivalent to about 20 mg of Oxtriphylline, to a 200-mL volumetric flask, dilute with water to volume, and mix.
Chromatographic system
(see
Chromatography 621)—The liquid chromatograph is equipped with a 275-nm detector and a 3.9-mm × 30-cm column that contains packing L1. The flow rate is about 1 mL per minute. Chromatograph the
System suitability preparation, and record the peak responses as directed for
Procedure: the relative retention times are about 0.7 for theobromine and 1.0 for theophylline, and the resolution,
R, between the theobromine and theophylline peaks is not less than 3.0. 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%.
Procedure—
Separately inject equal volumes (about 10 µL) of the
Standard preparation and the
Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks.
[NOTE—The major peaks recorded in the chromatograms represent the theophylline moiety of oxtriphylline.
] Calculate the quantity, in mg, of C
7H
8N
4O
2 in the portion of Tablets taken by the formula:
(180.17 / 283.33)(20C / V)(rU / rS),
in which 180.17 and 283.33 are the molecular weights of anhydrous theophylline and oxtriphylline, respectively;
C is the concentration, in µg per mL, of
USP Oxtriphylline RS in the
Standard preparation; V is the volume, in mL, of solution taken for the
Assay preparation; and
rU and
rS are the theophylline peak responses obtained from the
Assay preparation and the
Standard preparation, respectively.
