Validated voltammetric method for the determination of some antiprotozoa drugs based on the reduction at an activated glassy carbon electrode

Rapid Entrapment of Phenazine Ethosulfate within a Polyelectrolyte Complex on Electrodes for Efficient NAD+ Regeneration in Mediated NAD+-Dependent Bioelectrocatalysis

Over the past two decades, the designs of redox polymers have become critical to the field of mediated bioelectrocatalysis and are used in commercial glucose biosensors, as well as other bioelectrochemical applications (e.g., energy harvesting). These polymers are specifically used to immobilize redox mediators on electrode surfaces, allowing for self-exchange-based conduction of electrons from enzymes far from the electrode to the electrode surface. However, the synthesis of redox polymers is challenging and results in large batch-to-batch variability. Herein, we report a rapid entrapment of mediators for NAD⁺-dependent bioelectrocatalysis within reverse ionically condensed polyelectrolytes. A high ionic strength aqueous solution of oppositely charged polyelectrolytes, composed of cationic polyguanidinium (PG) chloride and anionic sodium hexametaphosphate (P6), undergoes phase inversion into a solid microporous polyelectrolyte complex (PEC) when introduced into a low ionic strength aqueous solution. The ionic strength-triggered phase inversion of PGP6 solutions was investigated as a means to entrap mediators on the surface of electrodes for mediated bioelectrocatalysis. Compared to the traditional cross-linked immobilizations using redox polymers, this phase inversion takes place within seconds and requires up to 60 min for complete stabilization. In this work, redox mediator phenazine ethosulfate (PES) was entrapped within PGP6 on electrode surfaces for nicotinamide adenine dinucleotide (NAD⁺)-dependent bioelectrocatalysis. In the bulk solution, NAD⁺-dependent dehydrogenase enzymes catalyze the oxidation of the substrate while reducing NAD to reduced nicotinamide adenine dinucleotide (NADH). The resulting NADH is reoxidized to NAD⁺ by the entrapped PES that gets reduced on the electrode, completing the NAD⁺-regeneration-based bioelectrocatalysis. To show the use of these new materials in an application, biofuel cells were evaluated using four different anodic enzyme systems (alcohol dehydrogenase, lactate hydrogenase, glycerol dehydrogenase, and glucose dehydrogenase).

Development of an electrochemical sensor based on a cobalt oxide/tin oxide composite for determination of antibiotic drug ornidazole

A schematic illustration of the electrochemical performance towards sensing of ODZ at the Co₃O₄/SnO₂/GCE.

Design of a Sensitive and Selective Voltammetric Sensor Based on a Cationic Surfactant-Modified Carbon Paste Electrode for the Determination of Alloxan

Alloxan (AL) is a toxic glucose analogue that acts as a potent diabetogenic inducer by selectively destroying the insulin-producing β-cells of the pancreas. Hence, a sensitive and selective cetyl trimethylammonium bromide (CTAB)-immobilized carbon paste electrode was utilized for the analysis of AL in the existence of anthrone. The CTAB-modified carbon paste electrode in contrast with the bare carbon paste electrode showed a magnificent behavior for the electrocatalytic oxidation of AL by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods. CV studies reveal a quasi-reversible diffusion-controlled process in the potential window of -0.5 to 0.4 V at an optimum pH of 6.5 in 0.2 M phosphate buffer solution. The electrode materials were characterized by CV, field emission-scanning electron microscopy, and electrochemical impedance spectroscopy. Under optimized experimental conditions, low detection limits of 1.09 and 3.64 μM were obtained in a linear dynamic range of 5-80 μM and from 8 to 90 μM by DPV and CV methods, respectively. The performance of the modified electrode is impressive in terms of least charge transfer resistance (R ct), surface concentration (Γ), and heterogeneous electron transfer rate constant (k 0). A 50-fold excess concentration of other potential interferants such as food additives and other organic species present in the human body does not significantly alter the peak potential and peak current of AL. The analytical application of the modified sensor was appraised by determining AL in the spiked refined flour sample. The modified sensor with a swift fabrication procedure exhibited enduring stability, adequate reproducibility, and acceptable repeatability.

Preparation and application of a carbon paste electrode modified with multi-walled carbon nanotubes and boron-embedded molecularly imprinted composite membranes

An innovative electrochemical sensor was fabricated for the sensitive and selective determination of tinidazole (TNZ), based on a carbon paste electrode (CPE) modified with multi-walled carbon nanotubes (MWCNTs) and boron-embedded molecularly imprinted composite membranes (B-MICMs). Density functional theory (DFT) calculations were carried out to investigate the utility of template-monomer interactions to screen appropriate monomers for the rational design of B-MICMs. The distinct synergic effect of MWCNTs and B-MICMs was evidenced by the positive shift of the reduction peak potential of TNZ at B-MICMs/MWCNTs modified CPE (B-MICMs/MWCNTs/CPE) by about 200 mV, and the 12-fold amplification of the peak current, compared with a bare carbon paste electrode (CPE). Moreover, the coordinate interactions between trisubstituted boron atoms embedded in B-MICMs matrix and nitrogen atoms of TNZ endow the sensor with advanced affinity and specific directionality. Thereafter, a highly sensitive electrochemical analytical method for TNZ was established by different pulse voltammetry (DPV) at B-MICMs/MWCNTs/CPE with a lower detection limit (1.25 × 10^-12 mol L^-1) (S/N = 3). The practical application of the sensor was demonstrated by determining TNZ in pharmaceutical and biological samples with good precision (RSD 1.36% to 3.85%) and acceptable recoveries (82.40%-104.0%).

Electrochemical Behaviour of Tinidazole at 1,4-Benzoquinone Modified Carbon Paste Electrode and Its Direct Determination in Pharmaceutical Tablets and Urine by Differential Pulse Voltammetry

A simple and highly sensitive electrochemical method based on a 1,4-benzoquinone modified carbon paste electrode (1,4-BQMCPE) was described for the determination of tinidazole (TDZ). In Britton Robinson buffer solution, TDZ yields well-defined irreversible reduction peak at -0.344 V on a 1,4-BQMCPE. Compared with that on a bare CPE, the reduction peak of TDZ increased significantly on the modified CPE and the effects of different parameters on the voltammetric responses were also investigated. Differential pulse voltammetric method was proposed and optimized for TDZ determination and its reductive peak current response at 1,4-BQMCPE was found to show linear dependence on the concentration of TDZ in the range of 1.0 × 10^-6 to 5.0 × 10^-4 M with a linear regression equation, correlation coefficient, limit of detection (LOD), and limit of quantification (LOQ) of I_PC (μA) = 0.19958 + 0.02657C (μM), 0.99486, 1.10 × 10^-7 M, and 3.77 × 10^-7, respectively. Excellent recovery results for spiked TDZ in pharmaceutical tablet samples ranging within 97.44-97.51% and in urine ranging within 95.37-96.91% were observed. The selectivity of the method for TDZ was further studied in the presence of selected potential interferents and confirmed the potential applicability of the developed method for the determination of TDZ.

Utility of Activated Glassy Carbon and Pencil Graphite Electrodes for Voltammetric Determination of Nalbuphine Hydrochloride in Pharmaceutical and Biological Fluids

This work compares voltammetric response of nalbuphine hydrochloride (NP·HCl) at both activated glassy carbon and pencil graphite electrodes. The electrochemical oxidation of the drug was studied using cyclic voltammetry (CV), differential pulse voltammetry (DPV), and square wave voltammetry (SWV) techniques. For analytical purpose a well-resolved irreversible diffusion controlled voltammetric peak was established in Britton-Robinson (B-R) buffer solution of pH 6.00 using pencil graphite electrode (PGE). Using activated glassy carbon electrode (GCE) a well-resolved irreversible diffusion controlled voltammetric peak was obtained at pH 7.00 using the same buffer solution. According to the linear relationship between the peak current and NP·HCl concentration, DPV and SWV methods were developed for their quantitative determination in pharmaceutical and human biological fluids. The linear response was obtained in the range from1.6×10-5to1.5×10-4 mol L−1using PGE and from12.5×10-6to13.75×10-5 mol L−1using a GC electrode, respectively. Precision and accuracy of the developed method were checked by recovery studies.