A: The retention time of the main peak in the chromatogram of the Assay preparationcorresponds to that in the chromatogram of the Standard preparation,obtained as directed in the Assay.

B: Ultraviolet Absorption á197Uñ—

Solution: 10µg of atenolol per mL.

Medium: methanol.

Citric acid buffer— Transfer 2.5g of citric acid to a 500-mLvolumetric flask,add 400mLof water,and swirl to dissolve.Adjust the solution with 2Nsodium hydroxide to a pHof 6.0,dilute with water to volume,and mix.

Mobile phase— Dissolve 930mg of sodium octyl sulfate in 740mLof water,add 8mLof 3.6Nsulfuric acid,mix,and pass through a 1-µm or finer porosity filter.To the filtrate add 250mLof acetonitrile,mix,and degas.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard preparation— Transfer about 50mg of USP Atenolol RSto a 100-mLvolumetric flask,add 80mLof Citric acid buffer,and sonicate for about 30seconds to achieve dissolution.Dilute with Citric acid bufferto volume,and mix.Transfer 4.0mLof this solution to a 10-mLvolumetric flask,dilute with Citric acid bufferto volume,and mix.This solution contains about 0.2mg of USP Atenolol RSper mL.

Assay preparation— Transfer an accurately measured volume of Injection,equivalent to 2mg of atenolol,to a 10-mLvolumetric flask,dilute with Citric acid bufferto volume,and mix.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 275-nm detector and a 4.6-mm ×25-cm column that contains 5-µm packing L1.The flow rate is about 1.7mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the tailing factor is not more than 2,and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 10µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the areas for the major peaks.Calculate the quantity,in mg,of C14H22N2O3in each mLof the Injection taken by the formula: in which Cis the concentration,in mg per mL,of USP Atenolol RSin the Standard preparation;Vis the volume,in mL,of Injection taken;and rUand rSare the atenolol peak responses obtained from the Assay preparationand the Standard preparation,respectively.