A: To a solution of 5 Tablets in 20 mL of water add 1 mL of 2 N sodium hydroxide and 2 drops of potassium permanganate TS: a green color is produced.

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

C: Weigh a portion of finely powdered Tablets, equivalent to about 100 mg of dyphylline, and transfer to a 200-mL volumetric flask. Add about 100 mL of water, shake by mechanical means for about 15 minutes, dilute with water to volume, and mix. Filter, and transfer 2 mL of the filtrate to a 100-mL volumetric flask, dilute with water to volume, and mix: the UV absorption spectrum of the solution exhibits maxima and minima at the same wavelengths as that of a solution of USP Dyphylline RS containing 10 µg per mL, concomitantly measured.

Medium: water; 900 mL.

Apparatus 1: 100 rpm.

Time: 45 minutes.

Procedure— Determine the amount of C10H14N4O4 dissolved from UV absorbances at the wavelength of maximum absorbance at about 273 nm of filtered portions of the solution under test, suitably diluted with water, in comparison with a Standard solution having a known concentration of USP Dyphylline RS in the same medium.

Tolerances— Not less than 75% (Q) of the labeled amount of C10H14N4O4 is dissolved in 45 minutes.

(Official January 1, 2007)

Mobile phase— Dissolve 1.4 g of monobasic potassium phosphate in 1350 mL of water in a 2-liter volumetric flask, add methanol to volume, and mix. Filter through a 0.5-µm porosity membrane filter. [NOTE—The composition may be varied to meet system suitability requirements.]

Standard preparation— Dissolve an accurately weighed quantity of USP Dyphylline RS in water to obtain a solution having a known concentration of about 200 µg per mL.

Assay preparation— Weigh and finely powder not less than 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 100 mg of dyphylline, to a 500-mL volumetric flask, add 200 mL of water, insert the stopper, and shake by mechanical means for 10 minutes. Add water to volume, and mix. Just prior to injection, filter about 5 mL through a 1.2-µm porosity 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 1.0 mL per minute. Chromatograph five replicate injections of the Standard preparation, and record the peak responses as directed under Procedure: the relative standard deviation is not more than 2.0%. The tailing factor is not more than 2.0.

Procedure— Inject separately equal volumes, accurately measured (about 10 µL), of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the peak responses. Calculate the quantity, in mg, of C10H14N4O4 in the portion of Tablets taken by the formula: in which C is the concentration, in µg per mL, of USP Dyphylline RS in the Standard preparation, and rU and rS are the dyphylline peak responses obtained from the Assay preparation and the Standard preparation, respectively.