pH6Acetate buffer— Dissolve 250g of sodium acetate in about 500mLof water in a 1000-mLvolumetric flask,add 5.0mLof glacial acetic acid,dilute with water to volume,and mix.

Standard preparation— Transfer about 25mg of USP Tetracaine Hydrochloride RS,accurately weighed,to a 100-mLvolumetric flask,dissolve in isopropyl alcohol,add isopropyl alcohol to volume,and mix.Transfer 2.0mLof this solution to another 100-mLvolumetric flask,add 2.0mLof pH6Acetate buffer,dilute with isopropyl alcohol to volume,and mix.The concentration of USP Tetracaine Hydrochloride RSin the Standard preparationis about 5µg per mL.

Assay preparation— Transfer an accurately weighed portion of Cream,equivalent to about 4.5mg of tetracaine,to a 50-mLbeaker,add 25mLof isopropyl alcohol,and warm on a steam bath to dissolve the specimen completely.Transfer the solution with the aid of isopropyl alcohol to a 100-mLvolumetric flask,dilute with isopropyl alcohol to volume,and mix.Transfer 10.0mLof this solution to another 100-mLvolumetric flask,add 2.0mLof pH6Acetate buffer,dilute with isopropyl alcohol to volume,and mix.

Procedure— Concomitantly determine the absorbances of the Assay preparationand the Standard preparationin 1-cm cells at the wavelength of maximum absorbance at about 310nm,with a suitable spectrophotometer,using a 1in 50solution of pH6Acetate bufferin isopropyl alcohol as the blank.Calculate the quantity,in mg,of C15H24N2O2in the portion of Cream taken by the formula: in which 264.36and 300.82are the molecular weights of tetracaine and tetracaine hydrochloride,respectively;Cis the concentration,in µg per mL,of USP Tetracaine Hydrochloride RSin the Standard preparation;and AUand ASare the absorbances of the Assay preparationand the Standard preparation,respectively.