A: Infrared Absorption 197M.

B: The retention time of the major peak in the chromatogram of the Assay preparation corresponds to that of the Standard preparation obtained as directed in the Assay.

Test solution: 10 mg per mL, in 0.25 M zinc acetate. Prepare the 0.25 M zinc acetate solution as follows. Mix 600 mL of water with 150 mL of glacial acetic acid and 54.9 g of zinc acetate, and stir to dissolve the zinc acetate. While stirring, add 150 mL of ammonium hydroxide, cool to room temperature, and adjust with ammonium hydroxide to a pH of 6.4. Transfer the solution to a 1000-mL volumetric flask, dilute with water to volume, and mix.

(Official January 1, 2007)

Phosphate solution— Dissolve 2.76 g of monobasic sodium phosphate in about 900 mL of water in a 1000-mL volumetric flask, and adjust with 1 N sodium hydroxide to a pH of 5.0. Dilute with water to volume, and mix.

Mobile phase— Prepare a filtered and degassed mixture of Phosphate solution and acetonitrile (96:4). Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparation— Dissolve an accurately weighed quantity of USP Lisinopril RS in water, and dilute quantitatively, and stepwise if necessary, with water to obtain a solution having a known concentration of about 0.3 mg per mL.

Assay preparation— Transfer about 30 mg of Lisinopril, accurately weighed, to a 100-mL volumetric flask, dissolve in water, dilute with water to volume, and mix.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 210-nm detector and a 4.6-mm × 25-cm column that contains 5-µm packing L7 and is maintained at a temperature of 50. The flow rate is about 1 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed under Procedure: the column efficiency determined from the analyte peak is not less than 180 theoretical plates, the tailing factor for the analyte peak is not more than 1.7, and the relative standard deviation for replicate injections is not more than 1.0%.

Procedure— Separately inject equal volumes (about 20 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of C21H31N3O5 in the portion of Lisinopril taken by the formula: in which C is the concentration, in mg per mL, of USP Lisinopril RS in the Standard preparation, calculated on the anhydrous basis; and rU and rS are the lisinopril peak responses obtained from the Assay preparation and the Standard preparation, respectively.