A: Infrared Absorption 197K: previously dried over phosphorus pentoxide for 3 hours.

B: Ultraviolet Absorption 197U—

C: Dissolve about 20 mg in 10 mL of water with the aid of a few drops of 3 N hydrochloric acid, and add 5 drops of a solution of sodium nitrite (1 in 10), followed by 2 mL of a solution of 100 mg of 2-naphthol in 5 mL of 1 N sodium hydroxide: an orange-red precipitate is formed.

Test solution: dehydrated alcohol.

Standard solution: dehydrated alcohol.

Application volume: 10 µL.

Eluant: chloroform containing about 0.75% of dehydrated alcohol as a preservative, in a nonequilibrated chamber.

Visualization: 1.

Limit— The total of any ordinary impurities observed does not exceed 1%.

Aqueous solution— To 980 mL of water, add 20 mL of acetic acid and 1 mL of triethylamine, and mix well. The pH should be between 2.95 and 3.0; adjust as needed.

Mobile phase— Prepare a filtered and degassed mixture of Aqueous solution and methanol (60:40).

Standard preparation— Dissolve an accurately weighed quantity of USP Benzocaine RS in Mobile phase, and dilute quantitatively, and stepwise if necessary, with Mobile phase to obtain a solution having a known concentration of about 0.024 mg per mL.

Assay preparation— Transfer about 24 mg of Benzocaine, accurately weighed, to a 100-mL volumetric flask, dissolve in and dilute with Mobile phase to volume, and mix. Dilute 10 mL of this solution with Mobile phase to 100 mL.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 285-nm detector and a 2.0-mm × 15-cm column that contains 5-µm packing L11. The flow rate is about 0.2 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the tailing factor of the benzocaine peak is not more than 2.0; and the relative standard deviation for replicate injections is not more than 2.0%.

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 benzocaine peaks. Calculate the quantity, in mg, of C9H11NO2 in the portion of Benzocaine taken by the formula: in which C is the concentration, in mg per mL, of USP Benzocaine RS in the Standard preparation; rU and rS are the peak responses obtained from the Assay preparation and Standard preparation, respectively; and 1000 is the dilution factor for the Assay preparation.