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

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

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

Medium: water;900mL.

Apparatus 1: 100rpm.

Time: 45minutes.

Procedure— Determine the amount of C10H14N4O4dissolved from UVabsorbances at the wavelength of maximum absorbance at about 273nm 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 RSin the same medium.

Tolerances— Not less than 75%(Q)of the labeled amount of C10H14N4O4is dissolved in 45minutes.

Mobile phase— Dissolve 1.4g of monobasic potassium phosphate in 1350mLof 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 RSin water to obtain a solution having a known concentration of about 200µg per mL.

Assay preparation— Weigh and finely powder not less than 20Tablets.Transfer an accurately weighed portion of the powder,equivalent to about 100mg of dyphylline,to a 500-mLvolumetric flask,add 200mLof water,insert the stopper,and shake by mechanical means for 10minutes.Add water to volume,and mix.Just prior to injection,filter about 5mLthrough a 1.2-µm porosity membrane filter.

Chromatographic system (see Chromatography á621ñ)—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 1.0mLper 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 10µL),of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the peak responses.Calculate the quantity,in mg,of C10H14N4O4in the portion of Tablets taken by the formula: in which Cis the concentration,in µg per mL,of USP Dyphylline RSin the Standard preparation,and rUand rSare the dyphylline peak responses obtained from the Assay preparationand the Standard preparation,respectively.