A fixed time kinetic spectrophotometric method has been developed for the selective determination of metformin hydrochloride in bulk and in tablet formulation. This experiment indicates that at room temperature alkaline solution metformin is oxidized to β-diketone by the action of sodium hypochlorite, the product is subsequently reacts with sodium nitroprusside to give a green colored 1, 3 dinitrosyl-N’-(iminomethyl)-N, N-dimethyl formamidine complex with maximum absorption at 685 nm. In sodium hydroxide-boric acid buffer solution, this time dependent chromophoric reaction reaches to a state of maximum absorbance within 5 minutes. At a preselected time of 5 minutes (after initiation of reaction) readings of maximum absorbance were adopted for constructing the calibration curve. Beer’s law is obeyed over the concentration range of 10-120 ηg.mL-1 with molar absorptivity and Sandell’s sensitivity of 6.335 x 104 Lmol-1.cm-1 and 0.0261 ηg.mL-1 respectively. The linear regression equation is A= 0.004 + 0.003C (ηg. mL-1) with a regression coefficient (r2=0.999). The percent recovery of the method is 100.04% with average relative error 0.038% and average relative standard deviation (RSD) 0.319%. The parameters with regard to determination of metformin by proposed method are optimized. The reaction mechanism and reaction stoichiometry is discussed. The proposed method was successfully applied for estimation of metformin in commercially available metformin tablets containing glibenclamide, glimepiride, glipizide and gliclazide. The average accuracy was found good, which was evaluated by comparison of the results obtained with those claimed by the manufacturer.
Metformin Determination, Sodium Nitroprusside, Sodium Hypochlorite, Metformin Hydrochloride, Glibenclamide, Glimepiride, Glipizide, Gliclazide