Standard preparation— Pipet 5 mL of dehydrated alcohol and 5 mL of acetone into a 200-mL volumetric flask containing 50 mL of water, add water to volume, and mix. Pipet 10 mL of this solution into a 200-mL volumetric flask, add water to volume, and mix.

Test preparation— Transfer an accurately measured volume of Oral Solution, equivalent to about 5 mL of alcohol, to a 200-mL volumetric flask containing about 30 mL of water. Pipet 5 mL of acetone into the flask, add water to volume, and mix. Pipet 10 mL of this solution into a 200-mL volumetric flask, add water to volume, and mix.

Chromatographic system— The gas chromatograph is equipped with a flame-ionization detector and contains a 75-cm × 4-mm column packed with 20% phase G20 on support S1AB, conditioned as directed (see Chromatography 621). The column is maintained at a temperature of about 85, and the injection port and detector block are maintained at about 175 and 225, respectively. Nitrogen is used as the carrier gas at a flow rate of about 18 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the resolution, R, is not less than 2.0; the tailing factor of the alcohol peak is not greater than 1.5; and the relative standard deviation for replicate injections is not more than 2.0% in the ratio of the peak of alcohol to the peak of acetone.

Procedure— Separately inject equal volumes (about 4 µL) of the Test preparation and the Standard preparation, in duplicate, into the gas chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the percentage of alcohol in the specimen taken by the formula: in which V is the volume, in mL, of Oral Solution taken, and RU and RS are the peak response ratios of alcohol to that of acetone obtained from the Assay preparation and the Standard preparation, respectively: the alcohol content, obtained as the average of the calculated results, is between 90.0% and 110.0% of the labeled amount of C2H5OH.

(Official January 1, 2007)

Mobile phase and Chromatographic system— Prepare as directed in the Assay under Dyphylline Tablets.

Standard preparation— Dissolve an accurately weighed quantity of USP Dyphylline RS in Mobile phase to obtain a solution having a known concentration of about 500 µg per mL.

Assay preparation— Transfer an accurately measured volume of Oral Solution, equivalent to about 100 mg of dyphylline, to a 200-mL volumetric flask, add Mobile phase to volume, and mix.

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. Calculate the quantity, in mg, of dyphylline (C10H14N4O4) in the volume of Oral Solution 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.