Diluent, Mobile phase,Standard preparation,and Chromatographic system—Proceed as directed in the Assayunder Benzocaine,Butamben,and Tetracaine Hydrochloride Topical Solution.

Assay preparation— Fit the valve of the Topical Aerosol container with a cannula,and expel the contents of the container into a 100-mL,glass-stoppered round-bottom flask.Attach the flask to a rotary evaporator,and evaporate under a vacuum of about 600mm of mercury for about 2.5hours.Transfer an accurately weighed portion of the material in the round-bottom flask,equivalent to about 1400mg of benzocaine,to a 100-mLvolumetric flask.Add about 75mLof methanol,and mix.Sonicate for about 1minute,dilute with methanol to volume,and mix.Transfer 10.0mLof this solution to a second 100-mLvolumetric flask,add about 75mLof Diluent,shake,dilute with Diluentto volume,and mix.

Procedure— Proceed as directed for Procedurein the Assayunder Benzocaine,Butamben,and Tetracaine Hydrochloride Topical Solution.Calculate the individual quantities,in mg,of benzocaine (C9H11NO2),butamben (C11H15NO2),and tetracaine hydrochloride (C15H24N2O2·HCl)in the portion of the residue of Topical Aerosol taken from the round-bottom flask by the formula: in which Cis the concentration,in mg per mL,of the appropriate Reference Standard in the Standard preparation;and rUand rSare the peak responses of the corresponding analyte obtained from the Assay preparationand the Standard preparation,respectively.