Identification—
A: Infrared Absorption 
197K
.
Test specimen—
Transfer a quantity of powdered Tablets, equivalent to about 20 mg of metformin hydrochloride, to a suitable flask, add 20 mL of dehydrated alcohol, and shake. Filter, evaporate the filtrate on a water bath to dryness, and dry the residue at 105
for 1 hour.
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.
Related compounds—
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 for
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.
The area of any secondary peak in the chromatogram of the Test solution is not greater than the area of the major peak in the chromatogram of the Diluted test solution; and the sum of the areas of all secondary peaks in the chromatogram of the Test solution is not greater than six times the area of the major peak in the chromatogram of the Diluted test solution: not more than 0.1% of any impurity is found; and not more than 0.6% of total impurities is found.
Assay—
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 (C
4H
11N
5·HCl) in the portion of Tablets taken by the formula:
10C(AU / AS),
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
Standard preparation and the
Assay preparation, respectively.
