Mobile phase— Dissolve 0.81 g of dl-10-camphorsulfonic acid and 0.70 g of sodium acetate in 700 mL of water. Add 300 mL of methanol, mix, and pass through a membrane filter having a 0.5-µm or finer porosity.

Standard solution— Dissolve an accurately weighed quantity of USP Dimenhydrinate RS in methanol to obtain a Standard stock solution having a known concentration of about 0.5 mg per mL. Retain a portion of this Standard stock solution for use in the Assay. Pipet 5 mL into a 50-mL volumetric flask, dilute with methanol to volume, mix, and pass through a membrane filter having a 0.5-µm or finer porosity.

Test solution— Transfer an accurately measured volume of Injection, equivalent to about 50 mg of dimenhydrinate, to a 100-mL volumetric flask, dilute with methanol to volume, and mix to obtain a stock solution. Retain a portion of this stock solution for use in the Assay. Pipet 5 mL of this stock solution into a 50-mL volumetric flask, dilute with methanol to volume, mix, and pass through a membrane filter having a 0.5-µm or finer porosity.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 280-nm detector, a 2-mm × 12.5-cm guard column that contains packing L2, and a 4.6-mm × 25-cm analytical column that contains packing L1. The flow rate is about 2 mL per minute. Chromatograph three replicate injections of the Standard solution, and record the peak responses as directed for Procedure: the relative standard deviation is not more than 1.0%.

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 responses for the major peaks. Calculate the quantity, in mg, of 8-chlorotheophylline (C7H7ClN4O2) in each mL of the Injection taken by the formula: in which 214.61 and 469.96 are the molecular weights of 8-chlorotheophylline and dimenhydrinate, respectively; C is the concentration, in mg per mL, of USP Dimenhydrinate RS in the Standard solution; V is the volume, in mL, of Injection taken; and rU and rS are the peak responses 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.

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

Standard preparation— Use a portion of the Standard stock solution that was prepared for the Standard solution in the test for Content of 8-chlorotheophylline. Mix 5.0 mL of this Standard stock solution and 5.0 mL of Internal standard solution, and pass through a membrane filter having a 0.5-µm or finer porosity.

Assay preparation— Use a portion of the stock solution that was prepared for the Test solution in the test for Content of 8-chlorotheophylline. Mix 5.0 mL of this stock solution and 5.0 mL of Internal standard solution, and pass through a membrane filter having a 0.5-µm or finer porosity.

Procedure— Proceed as directed for Procedure in the Assay under Dimenhydrinate Tablets. Calculate the quantity, in mg, of dimenhydrinate (C17H21NO·C7H7ClN4O2) in each mL of the Injection taken by the formula: in which C is the concentration of USP Dimenhydrinate RS in the Standard preparation; V is the volume, in mL, of Injection taken; and the other terms are as defined therein.