A: Infrared Absorption 197M.

B: It meets the requirements of the flame test for Sodium 191.

Borate solution and Diluent— Prepare as directed in the Assay.

Buffer solution— Transfer 5.88 g of sodium citrate dihydrate and 2.84 g of anhydrous dibasic sodium phosphate to a 2-L volumetric flask, dilute with water to volume, and mix. Adjust with phosphoric acid to a pH of 8, and pass the solution through a filter having a 0.5-µm or finer porosity.

9-Fluorenylmethyl chloroformate solution— Prepare a solution in acetonitrile containing about 4 mg of 9-fluorenylmethyl chloroformate per mL. Prepare this solution fresh just prior to use.

Solution A— Prepare a filtered and degassed mixture of Buffer solution and acetonitrile (17:3).

Solution B— Prepare a filtered and degassed mixture of acetonitrile and Buffer solution (7:3).

Mobile phase— Use variable mixtures of Solution A and Solution B as directed for Chromatographic system. Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard stock solution— Prepare a solution of USP Alendronate Sodium RS in Diluent having a known concentration of about 0.6 mg per mL.

Standard solution— Transfer 5.0 mL of the Standard stock solution to a 50-mL polypropylene, screw-cap centrifuge tube containing 5 mL of Borate solution. Add 5 mL of acetonitrile and 5 mL of 9-Fluorenylmethyl chloroformate solution, and shake for 45 seconds. Allow to stand at room temperature for 30 minutes. Add 20 mL of methylene chloride, and shake vigorously for 1 minute. Centrifuge for 5 to 10 minutes, and use a portion of the clear upper aqueous layer.

Diluted standard solution— Dilute a portion of the Standard stock solution with Diluent to obtain a solution having a known concentration of about 0.6 µg per mL. Using 5 mL of this solution, proceed as directed for the Standard solution, beginning with “to a 50-mL polypropylene, screw-cap centrifuge tube.”

Reagent blank— Using a 5.0-mL portion of Diluent, proceed as directed for Standard solution, beginning with “to a 50-mL polypropylene, screw-cap centrifuge tube.”

Test solution— Transfer about 30 mg of Alendronate Sodium, accurately weighed, to a 50-mL volumetric flask, dissolve in and dilute with Diluent to volume, and mix. Using a 5.0-mL volume of this solution, proceed as directed for Standard solution, beginning with “to a 50-mL polypropylene, screw-cap centrifuge tube.”

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 266-nm detector and a 4.1-mm × 25-cm column that contains packing L21. The flow rate is about 1.8 mL per minute. The column temperature is maintained at about 45. The chromatograph is programmed as follows. Chromatograph the Standard solution and the Diluted standard solution, and record the peak responses as directed for Procedure: the tailing factor for the main peak in the chromatogram of the Standard solution is not more than 2.0; and the peak at that locus in the chromatogram of the Diluted standard solution is detectable with a signal-to-noise ratio of not less than 3.

Procedure— Separately inject equal volumes (about 20 µL) of the Test solution and the Reagent blank into the chromatograph, record the chromatograms, and measure the responses for all the peaks. Disregard any peak corresponding to those obtained from the Reagent blank. Calculate the percentage of each impurity in the portion of Alendronate Sodium taken by the formula: in which ri is the area of each impurity peak, and rs is the sum of all impurity peaks and the main peak: not more than 0.1% of any individual impurity is found, and not more than 0.5% of total impurities is found.

Buffer solution— Transfer 14.7 g of sodium citrate dihydrate and 7.05 g of anhydrous dibasic sodium phosphate to a 1-L volumetric flask, dilute with water to volume, mix, and adjust with phosphoric acid to a pH of 8.

Diluent— Dissolve 29.4 g of sodium citrate dihydrate in water in a 1-L volumetric flask, dilute with water to volume, and mix.

Borate solution— Dissolve 19.1 g of sodium borate in water in a 1-L volumetric flask, dilute with water to volume, and mix.

9-Fluorenylmethyl chloroformate solution— Prepare a solution in acetonitrile containing about 0.5 mg of 9-fluorenylmethyl chloroformate per mL. Prepare this solution fresh just prior to use.

Mobile phase— Prepare a filtered and degassed mixture of Buffer solution, acetonitrile, and methanol (70:25:5). Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard stock preparation— Prepare a solution of USP Alendronate Sodium RS in Diluent having a known concentration of about 0.1 mg per mL. Calculate the concentration, CS, of anhydrous alendronate sodium in this solution.

Standard preparation— Transfer 5.0 mL of the Standard stock preparation to a 50-mL polypropylene, screw-cap centrifuge tube containing 5 mL of Borate solution. Add 5 mL of 9-Fluorenylmethyl chloroformate solution, and shake for 30 seconds. Allow to stand at room temperature for 25 minutes. Add 25 mL of methylene chloride, and shake vigorously for 1 minute. Centrifuge for 5 to 10 minutes. Use a portion of the clear upper aqueous layer.

Reagent blank— Using 5.0 mL of Diluent, proceed as directed for Standard preparation, beginning with “to a 50-mL polypropylene, screw-cap centrifuge tube.”

Assay stock preparation— Transfer about 25 mg of Alendronate Sodium, accurately weighed, to a 250-mL volumetric flask, dissolve in and dilute with Diluent to volume, and mix.

Assay preparation— Using 5.0 mL of the Assay stock preparation, proceed as directed for the Standard preparation, beginning with “to a 50-mL polypropylene, screw-cap centrifuge tube.”

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 266-nm detector and a 4.1-mm × 25-cm column that contains packing L21. The flow rate is about 1.2 mL per minute. The column temperature is maintained at about 35. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the column efficiency is not less than 1500 theoretical plates, the tailing factor is not more than 1.5, 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, the Assay preparation, and the Reagent blank into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of C4H12NNaO7P2 in the portion of Alendronate Sodium taken by the formula: in which D is the dilution factor for the Assay stock preparation; CS is as defined under the Standard stock preparation; and rU and rS are the peak area responses for alendronic acid obtained from the Assay preparation and the Standard preparation, respectively.