Organoclay-modified electrodes: preparation, characterization and recent electroanalytical applications

Electrochemical Determination of Epinephrine in Pharmaceutical Preparation Using Laponite Clay-Modified Graphene Inkjet-Printed Electrode

Epinephrine (EP, also called adrenaline) is a compound belonging to the catecholamine neurotransmitter family. It can cause neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, Huntington's disease and amyotrophic lateral sclerosis. This work describes an amperometric sensor for the electroanalytical detection of EP by using an inkjet-printed graphene electrode (IPGE) that has been chemically modified by a thin layer of a laponite (La) clay mineral. The ion exchange properties and permeability of the chemically modified electrode (denoted La/IPGE) were evaluated using multi-sweep cyclic voltammetry, while its charge transfer resistance was determined by electrochemical impedance spectroscopy. The results showed that La/IPGE exhibited higher sensitivity to EP compared to the bare IPGE. The developed sensor was directly applied for the determination of EP in aqueous solution using differential pulse voltammetry. Under optimized conditions, a linear calibration graph was obtained in the concentration range between 0.8 µM and 10 μM. The anodic peak current of EP was directly proportional to its concentration, leading to detection limits of 0.34 μM and 0.26 μM with bare IPGE and La/IPGE, respectively. The sensor was successfully applied for the determination of EP in pharmaceutical preparations. Recovery rates and the effects of interfering species on the detection of EP were evaluated to highlight the selectivity of the elaborated sensor.

Voltammetric quantitative analysis of vildagliptin in bulk form and spiked human serum at a modified electrode

The electrochemical behavior of Vildagliptin (VILD) was studied using the cyclic voltammetric technique in an aqueous Britton–Robinson (BR) universal buffer solution of various pH levels between 4.0 and 10 at a 5% calcium-montmorillonite clay modified with carbon paste electrode surface (5% Ca-MMT/CPE). The results exhibited an irreversible anodic peak at about 1.238 V versus Ag/AgCl, KCl (3 mol L−1). The anodic peak was found to be diffusion–adsorption controlled. The possible reaction mechanism is estimated taking into consideration of the calculated electrons and protons number transferred on the electrode/electrolyte interface using the cyclic voltammetric technique. VILD was found to adsorb onto the surface of 5% Ca-MMT/CPE in a monolayer surface coverage of 3.0 × 10−12 mol cm−2. A validated square wave voltammetry (SWV) technique for VILD determination was performed. The calibration curve of VILD onto the 5% Ca-MMT/CPE surface was linear in the concentration range of 1.0–110 nmol L−1 with the mean limits of detection and quantification was 0.285 and 0.950 nmol L−1, respectively, in the bulk form. The proposed procedure for the assay of VILD in bulk form, dosage form, and spiked human serum has the advantage of being simple, rapid, sensitive, and inexpensive compared to other analytical methods. The described method showed an excellent performance for the trace determination of VILD in its formulation without interference from excipients.

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Application of palladium nanoparticles supported organo-kaolinite for 4-chloro-2-nitroaniline catalytic reduction and electrochemical detection

Palladium nanoparticles (PdNPs) supported organo-kaolinite was used as a solid catalyst for the reduction and electrochemical detection of 4-chloro-2-nitroaniline (CNA). During the catalytic reduction in presence of NaBH4, the effects...

Surface functionalization of natural hydroxyapatite by polymerization of β-cyclodextrin: application as electrode material for the electrochemical detection of Pb(II)

A composite material prepared by polymerization of β-cyclodextrin (β-CD) on the surface of natural hydroxyapatite using citric acid as cross linker, was employed as electrode material for the detection of Pb(II). Hydroxyapatite was obtained from bovine bones, following a three-step procedure including pre-calcination, chemical treatment with (NH₄)₂HPO_4, and calcination. The structure and morphology of the pristine hydroxyapatite (NHAP_P0.5) and its functionalized counterpart (NHAP_p0.5-CA-β-CD) were examined using XRD, FTIR, and SEM. Upon deposition as thin film on a glassy carbon electrode (GCE), the ion exchange ability of NHAP_p0.5-CA-β-CD was exploited to elaborate a sensitive sensor for the detection of lead. The electroanalytical procedure was based on the chemical accumulation of Pb(II) ions under open-circuit conditions, followed by the detection of the preconcentrated species using differential pulse anodic stripping voltammetry. The reproducibility of the proposed method, based on a series of 8 measurements in a solution containing 2 μM Pb(II) gave a coefficient of variation of 1.27%. Significant parameters that can affect the stripping response of Pb(II) were optimized, leading to a linear calibration curve for lead in the concentration range of 2 × 10^-8 mol L^-1 - 20 × 10^-8 mol L^-1 (R² = 0.998). The detection limit (3S/m) and the sensitivity of the proposed sensor were 5.06 × 10^-10 mol L^-1 and 100.80 μA.μM^-1, respectively. The interfering effect of several ions expected to affect the determination of lead was evaluated, and the proposed sensor was successfully applied in the determination of Pb(II) ions in spring water, well water, river water and tap water samples.

A new sensor based on an amino-montmorillonite-modified inkjet-printed graphene electrode for the voltammetric determination of gentisic acid

An amperometric sensor based on an inkjet-printed graphene electrode (IPGE) modified with amine-functionalized montmorillonite (Mt-NH₂) for the electroanalysis and quantification of gentisic acid (GA) has been developed. The organoclay used as IPGE modifier was prepared and characterized by infrared spectroscopy, X-ray diffraction, scanning electron microscopy, CHN elemental analysis, and thermogravimetry. The electrochemical features of the Mt-NH₂/IPGE sensor were investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The sensor exhibited charge selectivity ability which was exploited for the electrochemical oxidation of GA. The GA amperometric response was high in acidic medium (Brinton-Robinson buffer, pH 2) due to favorable interactions between the protonated amine groups and the negatively charged GA. Kinetic studies were also performed by cyclic voltammetry, and the obtained electron transfer rate constant of 11.3 s^-1 indicated a fast direct electron transfer rate of GA to the electrode. An approach using differential pulse voltammetry was then developed for the determination of GA (at + 0.233 V vs. a pseudo Ag/Ag⁺ reference electrode), and under optimized conditions, the sensor showed high sensitivity, a wide working linear range from 1 to 21 μM (R² = 0.999), and a low detection limit of 0.33 μM (0.051 ± 0.01 mg L^-1). The proposed sensor was applied to quantify GA in a commercial red wine sample. The simple and rapid method developed using a cheap clay material could be employed for the determination of various phenolic acids.