A: Infrared Absorption 197K.

B: Ultraviolet Absorption 197U—

Solution: 20 µg per mL.

Medium: hydrochloric acid in methanol (1 in 1200).

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

Mobile phase— Prepare a mixture of 0.05 M sodium acetate, previously adjusted with glacial acetic acid to a pH of 5.0, and acetonitrile (65:35), and filter through a filter having a 0.5-µm or finer porosity. Make adjustments if necessary (see System Suitability under Chromatography 621). Decreasing the acetonitrile concentration results in less resolution between pindolol and impurities that elute on the tail of the pindolol peak; increasing the acetonitrile concentration results in less resolution between impurities with longer retention times.

Resolution solution— Prepare as directed for Resolution solution in the Assay.

Test solution— Use the stock solution used to prepare the Assay preparation in the Assay.

Chromatographic system (see Chromatography 621)— Proceed as directed in the Chromatographic system under the Assay.

Procedure— [NOTE—Use peak areas where peak responses are indicated.] Separately inject equal volumes (about 10 µL) of the Resolution solution and the Test solution into the chromatograph, record the chromatograms, and measure the responses for all of the peaks. Calculate the percentage of each impurity in the portion of Pindolol taken by the formula: in which C is the concentration, in mg per mL, of USP Pindolol RS in the Resolution solution, W is the weight, in mg, of the portion of Pindolol taken to prepare the Test solution, rU is the peak response of an individual impurity, and rS is the pindolol peak response obtained from the Resolution solution. Not more than 0.5% of any individual impurity is found, and the total of all impurities does not exceed 2.0%.

Solvent— Use dimethyl sulfoxide.

(Official January 1, 2007)

Mobile phase— Prepare a mixture of 0.05 M sodium acetate, previously adjusted with glacial acetic acid to a pH of 5.0, and acetonitrile (65:35), and filter through a filter having a 0.5-µm or finer porosity. Make adjustments if necessary (see System Suitability under Chromatography 621).

Resolution solution— Prepare a solution in Mobile phase having known concentrations of about 0.005 mg of USP Pindolol RS per mL and about 0.005 mg of indole per mL.

Standard preparation— Transfer about 100 mg of USP Pindolol RS, accurately weighed, to a 100-mL volumetric flask, add about 90 mL of Mobile phase, and dissolve by sonicating for about 5 minutes. Cool, dilute with Mobile phase to volume, and mix. Transfer 5.0 mL of this solution to a 50-mL volumetric flask, dilute with Mobile phase to volume, and mix.

Assay preparation— Transfer about 100 mg of Pindolol, accurately weighed, to a 100-mL volumetric flask, add about 90 mL of Mobile phase, and dissolve by sonicating for about 5 minutes. Cool, dilute with Mobile phase to volume, and mix. Transfer 5.0 mL of this stock solution to a 50-mL volumetric flask, dilute with Mobile phase to volume, and mix.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 219-nm detector and a 4.6-mm × 15-cm column containing 3-µm packing L10. The flow rate is about 1 mL per minute. Chromatograph the Resolution solution, and record the responses as directed for Procedure: the relative retention times are about 0.5 for indole and 1.0 for pindolol, the resolution, R, between the indole and pindolol is not less than 7, the column efficiency determined from the pindolol peak is not less than 3000 theoretical plates, and the relative standard deviation of the pindolol peak response for replicate injections is not more than 2%.

Procedure— [NOTE—Use peak areas where peak responses are indicated.] Separately inject equal volumes (about 10 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 C14H20N2O2 in the portion of Pindolol taken by the formula: in which C is the concentration, in mg per mL, of USP Pindolol RS in the Standard preparation, and rU and rS are the pindolol peak responses obtained from the Assay preparation and the Standard preparation, respectively.