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

B: Ultraviolet Absorption 197U—

Solution: 10 µg of atenolol per mL.

Medium: methanol.

(Official January 1, 2007)

Citric acid buffer— Transfer 2.5 g of citric acid to a 500-mL volumetric flask, add 400 mL of water, and swirl to dissolve. Adjust the solution with 2 N sodium hydroxide to a pH of 6.0, dilute with water to volume, and mix.

Mobile phase— Dissolve 930 mg of sodium octyl sulfate in 740 mL of water, add 8 mL of 3.6 N sulfuric acid, mix, and pass through a 1-µm or finer porosity filter. To the filtrate add 250 mL of acetonitrile, mix, and degas. Make adjustments if necessary (see System Suitability under Chromatography 621).

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

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

Chromatographic system (see Chromatography 621)—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 1.7 mL per 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 10 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the areas for the major peaks. Calculate the quantity, in mg, of C14H22N2O3 in each mL of the Injection taken by the formula: in which C is the concentration, in mg per mL, of USP Atenolol RS in the Standard preparation; V is the volume, in mL, of Injection taken; and rU and rS are the atenolol peak responses obtained from the Assay preparation and the Standard preparation, respectively.