Mobile phase— Dissolve 0.20 g of monobasic potassium phosphate and 0.45 mL of n-heptylamine in about 350 mL of water. Adjust with phosphoric acid to a pH of 3.0, dilute with water to 400 mL, add 600 mL of acetonitrile, and mix.

Standard preparation— Dissolve an accurately weighed quantity of USP Dyclonine Hydrochloride RS in 0.001 N phosphoric acid to obtain a solution having a known concentration of about 0.1 mg per mL.

Assay preparation— Transfer an accurately measured portion of Gel, equivalent to about 5.0 mg of dyclonine hydrochloride, to a 50-mL volumetric flask. Add 10 mL of 0.001 N phosphoric acid, and sonicate to dissolve the gel. Dilute with 0.001 N phosphoric acid to volume, and mix.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 254-nm detector and a 4-mm × 25-cm column that contains 5-µm diameter packing L13. The flow rate is about 1.2 mL per minute. Adjust the flow rate, if necessary, so that the retention time of dyclonine hydrochloride is not less than 5 minutes. Chromatograph five replicate injections of the Standard preparation, and record the peak responses as directed for Procedure: the tailing factor is not more than 2.0 and the relative standard deviation is not more than 3.0%.

Procedure— Separately inject equal volumes (about 20 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 dyclonine hydrochloride (C18H27NO2·HCl) in the portion of Gel taken by the formula: in which C is the concentration, in mg per mL, of USP Dyclonine Hydrochloride RS in the Standard preparation, and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.