A: The retention time exhibited by theophylline in the chromatogram of the Assay preparationcorresponds to that of theophylline in the chromatogram of the Standard preparation,as obtained in the Assay.

B: Place a volume of Oral Solution,equivalent to about 100mg of oxtriphylline,in a 60-mLseparator containing 1mLof glacial acetic acid and 40mLof chloroform.Shake for 1minute,allow the phases to separate,and filter the lower phase through dry cotton into a 100-mLbeaker.Transfer a portion of the chloroform solution,equivalent to about 10mg of oxtriphylline,to a porcelain dish,and evaporate on a steam bath with the aid of a current of dry air to dryness.Add 1mLof hydrochloric acid and 100mg of potassium chlorate,evaporate on a steam bath to dryness,and invert the dish over a vessel containing a few drops of 6Nammonium hydroxide:the residue acquires a purple color.

Mobile phase,Standard preparation,System suitability preparation,and Chromatographic system— Prepare as directed in the Assayunder Oxtriphylline Delayed-release Tablets.

Assay preparation— Transfer an accurately measured volume of Oral Solution,equivalent to about 100mg of oxtriphylline,to a 1000-mLvolumetric flask,dilute with water to volume,and mix.

Procedure— Proceed as directed for Procedurein the Assayunder Oxtriphylline Delayed-release Tablets.Calculate the quantity,in mg,of C7H8N4O2in each mLof the Oral Solution taken by the formula: in which Vis the volume,in mL,of Oral Solution taken to prepare the Assay preparation,and the other terms are as defined therein.