Ammonium bicarbonate solution, Diluent, Solution A, Solution B, Mobile phase, Internal standard solution, and Chromatographic system— Proceed as directed in the Assay under Dimenhydrinate Tablets.

Standard solution— Prepare as directed for Standard preparation in the Assay under Dimenhydrinate Tablets.

Test solution— Prepare as directed for Assay preparation in the Assay.

Procedure— Separately inject equal volumes (about 10 µL) of the Standard solution and the Test solution into the chromatograph, record the chromatograms, and measure the areas for the major peaks. Calculate the quantity, in mg per mL, of 8-chlorotheophylline (C7H7ClN4O2) in the portion of Oral Solution taken by the formula: in which 214.61 and 469.96 are the molecular weights of 8-chlorotheophylline and dimenhydrinate, respectively; W is the weight, in mg, of USP Dimenhydrinate RS in the Standard solution; and RU and RS are peak area ratios of 8-chlorotheophylline to the internal standard obtained from the Test solution and the Standard solution, respectively. An amount of 8-chlorotheophylline that is between 43.4% and 47.9% of the amount of dimenhydrinate obtained in the Assay is found.

Ammonium bicarbonate solution, Diluent, Solution A, Solution B, Mobile phase, Internal standard solution, Standard preparation, and Chromatographic system— Proceed as directed in the Assay under Dimenhydrinate Tablets.

Assay preparation— Pipet 5.0 mL of Oral Solution into a suitable container, add 5.0 mL of Internal standard solution, and mix. Transfer about 1 mL of this solution to a suitable container, add about 5 mL of Diluent, and mix.

Procedure— Proceed as directed for Procedure in the Assay under Dimenhydrinate Tablets. Calculate the quantity, in mg per mL, of dimenhydrinate (C17H21NO·C7H7ClN4O2) in the portion of the Oral Solution taken by the formula: in which W is the weight, in mg, of USP Dimenhydrinate RS in the Standard preparation; and RU and RS are the peak area ratios of diphenhydramine to the internal standard obtained from the Assay preparation and the Standard preparation, respectively.