Related compounds—
Mobile phase—
Prepare a solution in water, containing 17 g of monobasic ammonium phosphate per L, adjust with phosphoric acid to a pH of 3.0, and mix.
Standard solution—
Prepare a solution of USP Metformin Related Compound A RS in water having a known concentration of about 0.2 mg per mL. Transfer 1.0 mL of this solution to a 200-mL volumetric flask, dilute with
Mobile phase to volume, and mix.
[NOTE—Metformin related compound A is 1-cyanoguanidine.
]
Test solution—
Transfer about 500 mg of Metformin Hydrochloride, accurately weighed, to a 100-mL volumetric flask, dissolve in and dilute with Mobile phase to volume, and mix.
Diluted test solution—
Transfer 1.0 mL of the Test solution to a 10-mL volumetric flask, dilute with Mobile phase to volume, and mix. Transfer 1.0 mL of this solution to a 100-mL volumetric flask, dilute with Mobile phase to volume, and mix.
Resolution solution—
Transfer about 10 mg of melamine to a 100-mL volumetric flask, and dissolve in about 90 mL of water. Add 5.0 mL of the Test solution, dilute with water to volume, and mix. Transfer 1.0 mL of this 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 218-nm detector and a 4.6-mm × 25-cm column containing packing L9. The flow rate is about 1.0 to 1.7 mL per minute. Chromatograph the
Resolution solution, and record the peak responses as directed for
Procedure: the resolution,
R, between melamine and metformin is not less than 10.
Procedure—
Separately inject equal volumes (about 20 µL) of the
Test solution, the
Standard 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 a peak corresponding to metformin related compound A in the chromatogram of the
Test solution is not greater than the area of the corresponding peak in the chromatogram of the
Standard solution: not more than 0.02% of metformin related compound A is found.
The area of any other 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 five times the area of the major peak in the chromatogram of the Diluted test solution: not more than 0.1% of any other impurity is found; and not more than 0.5% of total impurities is found.
Assay—
[NOTE—To avoid overheating of the reaction medium, mix thoroughly throughout the titration, and stop the titration immediately after the endpoint has been reached.
] Dissolve about 60 mg of Metformin Hydrochloride, accurately weighed, in 4 mL of anhydrous formic acid. Add 50 mL of acetic anhydride. Titrate with 0.1 N perchloric acid VS, determining the endpoint potentiometrically. Perform a blank determination, and make any necessary correction (see
Titrimetry 541). Each mL of 0.1 N perchloric acid is equivalent to 8.28 mg of C
4H
11N
5·HCl.
;)
Packaging and storage—
Preserve in well-closed containers. Store at room temperature.
for 5 hours: it loses not more than 0.5% of its weight.