Application of novel oligomeric Co(II) complexes of 4,4′-bipyridine and 1,10-phenanthroline modified glassy carbon electrode for differential pulse voltammetric determination of ciprofloxacin

Two new oligomer mixed ligand complexes, comprising 21 ([Co₂₁(phen)₄₂(bipy)₂₁]Cl₄₂ (C2)) and 100 monomer units ([Co₁₀₀(phen)₂₀₀(bipy)₁₀₀]Cl₂₀₀ (C3)) were synthesized. These complexes, designated as [Co₂₁(phen)₄₂(bipy)₂₁]Cl₄₂ (C2) and [Co₁₀₀(phen)₂₀₀(bipy)₁₀₀]Cl₂₀₀ (C3), were employed for the modification of a glassy carbon electrode (GCE) to detect ciprofloxacin (CPF) in tablet formulations and human urine samples. By potentiodynamic deposition, the modified electrodes (poly(C2)/GCE) and (poly(C3)/GCE) were prepared, forming a conductive electroactive film on the GCE surface. The modified electrodes were characterized using cyclic voltammetry and electrochemical impedance spectroscopy, which revealed an increased effective surface area and a significant reduction in charge transfer resistance of the electrode. An oxidative peak at a lower potential with a six-fold increase in peak current was observed at the poly(C2)/GCE. The absence of a reductive peak in the reverse scan indicated the irreversibility of the electrochemical oxidation of CPF. The correlation coefficient between the peak current and the square root of the scan rate indicated that CPF oxidation at the poly(C2)/GCE was primarily controlled by diffusion mass transport. With a detection limit of 3.4 × 10⁻⁹ M, the voltammetric current response of CPF at the poly(C2)/GCE under optimal circumstances showed a linear trend with concentrations ranging from 5.0 × 10⁻⁸ to 2.0 × 10⁻⁴ M. It was discovered that the CPF levels in the examined tablet brands fell between 98.35 % and 101.30 % of their stated ranges. The recovery results for tablet and urine samples ranged from 99.44 % to 99.95 % and 99.25 % to 100.51 %, respectively, with interference recovery showing an error of less than 4.73 %. When it came to determining CPF in tablet formulations and human urine samples, the new approach outperformed recently published voltammetric methods. This superiority can be attributed to the simplicity of the electrode modification step, the lowest limit of detection, and a reasonably wide linear dynamic range.