Test solution: 10mg per mL,in chloroform.

Mobile phase— Prepare a mixture of methanol and 0.067Mmonobasic potassium phosphate (650:350),adjust with phosphoric acid to a pHof 4.0,pass through a filter having a porosity of 0.5µm or finer,and degas.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard preparation— Dissolve an accurately weighed quantity of USP Clarithromycin RSquantitatively in methanol,shaking and sonicating if necessary to assure dissolution,to obtain a stock solution having a known concentration of about 625µg of clarithromycin (C38H69NO13)per mL,taking into account the stated potency,in µg per mg,of USP Clarithromycin RS.Transfer 10.0mLof this stock solution to a 50-mLvolumetric flask,dilute with Mobile phaseto volume,and mix.Pass through a filter having a porosity of 0.5µm or finer,and use the filtrate as the Standard preparation.This solution contains about 125µg of clarithromycin (C38H69NO13)per mL.

Resolution solution— Prepare a solution of USP Clarithromycin Related Compound A RSin methanol containing about 625µg per mL.Transfer 10mLof this solution and 10mLof the stock solution used to prepare the Standard preparationto a 50-mLvolumetric flask,dilute with Mobile phaseto volume,and mix.

Assay preparation— Transfer about 65mg of Clarithromycin,accurately weighed,to a 100-mLvolumetric flask,and add 80mLof methanol to dissolve,shaking and sonicating if necessary to assure dissolution.Dilute with methanol to volume,and mix.Transfer 10.0mLof this solution to a 50-mLvolumetric flask,dilute with Mobile phaseto volume,mix,and pass through a filter having a porosity of 0.5µm or finer.Use the filtrate as the Assay preparation.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 210-nm detector,an optional guard column that contains packing L1,a 4.6-mm ×15-cm column that contains packing L1,and is maintained at a constant temperature of about 50.The flow rate is about 1mLper minute.Chromatograph the Resolution solution,and record the responses as directed under Procedure:the relative retention times are about 0.75for clarithromycin and 1.0for clarithromycin related compound A,and the resolution,R,between the clarithromycin peak and the clarithromycin related compound Apeak is not less than 2.0.Chromatograph the Standard preparation,and record the responses as directed under Procedure:the column efficiency,determined from the clarithromycin peak,is not less than 750theoretical plates when calculated by the formula: the tailing factor is not less than 0.9and not more than 2,and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 20to 50µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the areas for the major peaks.Calculate the quantity,in µg,of C38H69NO13in each mg of the Clarithromycin taken by the formula: in which Cis the concentration,in µg per mL,of clarithromycin (C38H69NO13)in the Standard preparation,Mis the quantity,in mg,of Clarithromycin taken to prepare the Assay preparation,and rUand rSare the clarithromycin peak responses obtained from the Assay preparationand the Standard preparation,respectively.