A novel method to identify the metformin with a good selectivity has been established by using sodium nitroprusside as a chromogenic reagent. The experiment indicates that in basic solution sodium nitroprusside can react with the oxidized product (obtained by the action of sodium hypochlorite) of metformin to form a green colored 1, 3 dinitrosyl-N'-(iminomethyl)-N, N-dimethyl formamidine with maximum absorption at 680 nm. The test when compared with blank is sensitive for spectrophotometric detection of metformin up to 16.56 µg in 10 mL solution. The reaction stoichiometric ratio of the oxidized product of metformin to sodium nitroprusside is 1:2. The reaction mechanism of the green product is discussed in present investigation. The proposed method has been successfully applied for identification of metformin in aqueous solution containing glibenclamide, glimepiride, glipizide and gliclazide. Because of the dissociative nature of the green colored product, for a large linear range of microgram concentration of metformin the absorbance of the green colored product is not found to be linear. Hence it can concluded from this analysis that sodium nitroprusside is not suitable chromogenic reagent for spectrophotometric determination of metformin in aqueous solution.
Metformin, Metformin Identification, Sodium Nitroprusside, Sodium Hypochlorite