Procedure 2: Metformin Hydrochloride Buffer pH 3.5: 6.8 g/L of monobasic potassium phosphate (0.05 M). Adjust with phosphoric acid to a pH of 3.5. Mobile phase: Acetonitrile and Buffer pH 3.5 (18:82). [Note—To improve the resolution, the composition may be changed to (15:85), if necessary.] Dilute phosphoric acid: Transfer 1 mL of phosphoric acid to a 1-L volumetric flask, and dilute with water to volume. Diluent: Acetonitrile and Dilute phosphoric acid (5:95) Standard solution: 0.2 mg/mL of USP Metformin Hydrochloride RS in Diluent Sample stock solution: Place 5 Tablets into a 500-mL volumetric flask. Add about 150 mL of Diluent and shake for NLT 1.5 h or until the Tablets are completely dispersed. Dilute with Diluent to volume and mix. Allow the cloudy solution to settle for NLT 5 min. Sample solution: Nominally 0.2 mg/mL of metformin hydrochloride in Diluent from the Sample stock solution. Pass through a suitable filter, discarding the first few milliliters of the filtrate.