A Comprehensive Study of P-g-C3N4/MOF-199 Composite for Electrochemical Sensing of Metformin in Pharmaceutical Samples

A novel electrochemical sensor (P-g-C3N4/MOF-199/CPE) was developed to determine the metformin concentration in pharmaceutical samples. In this sensor, the copper units of MOF-199 of the composite electrode specifically capture metformin molecules so that the sensing selectivity is remarkably improved. Phosphorus-doped graphitic carbon nitrides (P-g-C3N4) further enhance the electrical conductivity and sensitivity of the sensor. The physical and chemical properties of these electrode modifiers were first characterized, followed by electrochemical sensing tests of metformin under different scan rates and pH values. A 39-fold increase in the electrooxidation current of metformin was found in this composite electrode when compared to its bare carbon paste counterpart. A limit of detection (LOD) of 0.15 nM was achieved in the linear sensing range of 0.5 to 1200 nM for metformin. The sensor also showed good reliability and recovery when detecting metformin in pharmaceutical samples. For the first time, we addressed the appearance of adsorption-based peaks in the voltammograms of electrochemical sensors for metformin as a common feature when copper ions are incorporated into the electrode structure. The electrochemical mechanism of metformin was also illustrated by highlighting the hydrolysis of oxime. The nature of all pH-dependent anodic and cathodic peaks in our sensing results confirms the proposed mechanism.