Pentacyanidoferrate(III) complex of metformin provides a simple colorimetric test for this important anti-hypoglycemic medicament

Metformin (MF) is one of the most important medicaments in the market. It has been extensively employed in the treatment of type -2 diabetes, but its analytical detection is rather complicated, requiring, for instance, highperformance chromatographic methods. Here, we report that metformin reacts with the pentacyanidoferrate (II) complex, generating a deep red product in the presence of sodium percarbonate, Na2CO3.1.5H2O2. A colorimetric assay has been performed by measuring the absorption band at 520 nm, with a limit of detection (LOD) of 0.018 mmol/L. The reaction can also be probed by Raman spectroscopy, since the [FeIII(CN)5MF]3- complex, exhibits a strong resonance effect which enhances the vibrational peaks of the iron(III)-guanidine chromophore. The Raman spectral features are associated with the Fe(III)-N--C-bonds and the metal-to-ligand charge-transfer transition, as confirmed by DFT calculations. (AU)