A: Infrared Absorption 197K.

B: Triturate a quantity of the powdered Tablets, equivalent to about 50 mg of metformin hydrochloride, with 10 mL of water, and filter. To 5 mL of the filtrate add 1.5 mL of 5 N sodium hydroxide solution and 1 mL of a 1-naphthol solution, prepared by dissolving 1 g of 1-naphthol in a solution containing 6 g of sodium hydroxide and 16 g of anhydrous sodium carbonate in 100 mL of water. Add 0.5 mL of sodium hypochlorite TS, dropwise, and with shaking: an orange-red color is produced that darkens on standing.

C: Triturate a quantity of the powdered Tablets, equivalent to about 50 mg of metformin hydrochloride, with 10 mL of water, and filter. The filtrate meets the requirements of the tests for Chloride 191.

test 1—

test 2— If the product complies with this test, the labeling indicates that it meets USP Dissolution Test 2.

Mobile phase, Resolution solution, and Chromatographic system— Proceed as directed in the test for Related compounds under Metformin Hydrochloride.

Test solution— Weigh and finely powder not fewer than 20 Tablets. Transfer a portion of the powder, equivalent to about 500 mg of metformin hydrochloride, to a 100-mL volumetric flask, dissolve in Mobile phase, with shaking, dilute with Mobile phase to volume, and mix. Filter, and use the filtrate.

Diluted test solution— Proceed as directed in the test for Related compounds under Metformin Hydrochloride, except to use the Test solution prepared as described herein.

Procedure— Separately inject equal volumes (about 20 µL) of the Test solution and the Diluted test solution into the chromatograph, record the chromatograms for not less than twice the retention time of metformin, and measure the peak areas.

Standard preparation— Prepare a solution of USP Metformin Hydrochloride RS in water having a known concentration of about 10 µg per mL.

Assay preparation— Weigh and finely powder not fewer than 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 100 mg of metformin hydrochloride, to a 100-mL volumetric flask. Add 70 mL of water, shake by mechanical means for 15 minutes, dilute with water to volume, and filter, discarding the first 20 mL of the filtrate. Dilute 10.0 mL of the filtrate with water to 100.0 mL, and dilute 10.0 mL of the resulting solution with water to 100.0 mL.

Procedure— Concomitantly determine the absorbances of the Standard preparation and the Assay preparation, in 1-cm cells, at the wavelength of maximum absorbance at about 232 nm, with a suitable spectrophotometer, using water as a blank. Calculate the quantity, in mg, of metformin hydrochloride (C4H11N5·HCl) in the portion of Tablets taken by the formula: in which C is the concentration, in µg per mL, of USP Metformin Hydrochloride RS in the Standard preparation; and AU and AS are the absorbances obtained from the Assay preparation and the Standard preparation, respectively.