Mobile phase— Dissolve 990mg of sodium 1-heptanesulfonate in 890mLof water,add 10mLof glacial acetic acid and 1100mLof methanol,mix,pass through a suitable filter having a 1-µm or finer porosity,and degas.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard preparation— Dissolve an accurately weighed quantity of USP Levobunolol Hydrochloride RSin Mobile phaseto obtain a solution having a known concentration of about 0.1mg per mL.

Assay preparation— Dilute an accurately measured volume of Ophthalmic Solution quantitatively,and stepwise if necessary,with Mobile phaseto obtain a solution containing about 0.1mg of levobunolol hydrochloride per mL.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 254-nm detector and a 4-mm ×30-cm column that contains packing L1.The flow rate is about 1.5mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the column efficiency determined from the analyte peak is not less than 1000theoretical plates;the capacity factor,k¢,for levobunolol is between 1.0and 1.4;the tailing factor for the analyte peak is not more than 2.6;and the relative standard deviation for replicate injections is not more than 1.5%.

Procedure— Separately inject equal volumes (about 30µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the area responses for the major peaks.Calculate the quantity,in mg,of C17H25NO3·HCl in each mLof the Ophthalmic Solution taken by the formula: in which Lis the labeled amount,in mg,of levobunolol hydrochloride in each mLof the Ophthalmic Solution;Dis the concentration,in mg per mL,of levobunolol hydrochloride in the Assay preparation,based on the labeled quantity per mLand the extent of dilution;Cis the concentration,in mg per mL,of USP Levobunolol Hydrochloride RSin the Standard preparation;and rUand rSare the peak area responses obtained from the Assay preparationand the Standard preparation,respectively.