Tetrahydrozoline Hydrochloride Ophthalmic Solution »Tetrahydrozoline Hydrochloride Ophthalmic Solution is a sterile,isotonic solution of Tetrahydrozoline Hydrochloride in water.It contains not less than 90.0percent and not more than 110.0percent of the labeled amount of C13H16N2·HCl. Packaging and storage— Preserve in tight containers. USP Reference standards á11ñ USP Tetrahydrozoline Hydrochloride RS. Identification— The UVabsorption spectrum of the Ophthalmic Solution,diluted with dilute hydrochloric acid (1in 100)to a concentration of about 1in 4000,exhibits maxima and minima at the same wavelengths as that of a similar solution of USP Tetrahydrozoline Hydrochloride RS,concomitantly measured. Sterility á71ñ: meets the requirements. pHá791ñ: between 5.8and 6.5. Assay— Standard preparation— Dissolve a suitable quantity of USP Tetrahydrozoline Hydrochloride RS,accurately weighed,in water,and dilute quantitatively with water to obtain a solution having a known concentration of about 500µg per mL. Procedure— Transfer 2.0mLof Standard preparationto a 50-mLvolumetric flask.Transfer an accurately measured volume of Ophthalmic Solution,equivalent to about 1mg of tetrahydrozoline hydrochloride,to a second 50-mLflask,and transfer 2mLof water to a third 50-mLvolumetric flask to provide a blank.To each flask add 5.0mLof bromophenol blue sodium salt solution (1in 1000),dilute each flask with potassium biphthalate solution (1in 100)to volume,and mix.Allow to stand for 20minutes,and filter each mixture through a suitable filter paper (Whatman No.42or the equivalent)that does not absorb the dye,discarding the first 15mLof the filtrate.Transfer 20.0mLof the subsequent filtrate to separate 125-mLseparators,and extract each solution with four 20-mLportions of chloroform,filtering each extract through a pledget of glass wool into a 100-mLvolumetric flask.Dilute the combined extracts from each solution with chloroform to volume,and mix.Concomitantly determine the absorbances of the solutions in 1-cm cells at the wavelength of maximum absorbance at about 415nm,with a suitable spectrophotometer,using the blank to set the instrument.Calculate the quantity,in µg,of C13H16N2·HCl in each mLof the Ophthalmic Solution taken by the formula: 2(C/V)(AU/AS), in which Cis the concentration,in µg per mL,of USP Tetrahydrozoline Hydrochloride RSin the Standard preparation,Vis the volume,in mL,of Solution taken,and AUand ASare the absorbances of the solutions from the Ophthalmic Solution and the Standard preparation,respectively. Auxiliary Information— Staff Liaison:Lawrence Evans,III,Ph.D.,Scientist Expert Committee:(PA6)Pharmaceutical Analysis 6 USP28–NF23Page 1893 Phone Number:1-301-816-8389