Miniaturized ionophore-based potentiometric sensors for the flow-injection determination of metformin in pharmaceutical formulations and biological fluids

Abstract

Miniaturized potentiometric sensors based on β-cyclodextrins (β-CDs) are described for determination of metformin (Mf) in pharmaceutical preparations and biological fluids. Electrode matrix compositions are optimized on the basis of the nature and content of sensing ionophore, ionic sites and plasticizers. Coated wire electrodes (CWEs) modified with heptakis(2,3,6-tri-O-methyl)-β-CD, sodium tetrakis(4-fluorophenyl)borate (NaTFPB) and 2-fluorophenyl 2-nitrophenyl ether (f-NPE), work satisfactorily in the concentration range from 10⁻⁶ to 10⁻¹ mol L⁻¹ with Nernstian compliance (55.7 ± 0.4 mV per decade activity) and a detection limit of 8 × 10⁻⁷ mol L⁻¹. Incorporation of β-CD as a molecular recognition element improved the electrode sensitivity and selectivity due to encapsulation of Mf into the β-CD cavity (host–guest interaction). The developed electrodes have been successfully applied for the potentiometric determination of Mf under batch and flow injection analysis (FIA). FIA allows analysis of 90 samples per h offering the advantages of simplicity, accuracy and automation feasibility. The dissolution profile for metformin pharmaceutical samples (Cidophage®) was monitored using the proposed electrode in comparison with the official spectrophotometric methods. Characterization of the formed Mf–β-CD inclusion complexes is discussed in detail.