Poly (naphthol green B) modified carbon paste electrode sensor for catechol and hydroquinone

Electrochemical sensor for the detection of adrenaline at poly(crystal violet) modified electrode: optimization and voltammetric studies

Herein, we report the electropolymerization of crystal violet (CRV) on a bare glassy carbon electrode (GCE) for the detection of adrenaline (AD). Electropolymerization parameters such as electrolyte pH, scan rate and monomer concentrations were optimized using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The characterization of CRV and poly(crystal violet) (PCV) was done using FT-IR, UV-visible spectroscopy and EIS. More importantly, the charge transfer resistance (R_ct) and other EIS data recorded from the EIS of various forms of the poly(crystal violet) (PCV) modified glassy carbon electrode (GCE) in AD were used for identifying the best PCV modified electrode. Subsequent application of the electrode prepared at optimum conditions (PGCE) for AD detection using the square wave voltammetry (SWV) gave a limit of detection (LOD) of 2.86 μM over a linear range of 10.3-102.7 μM. This sensor also showed considerable stability, good AD recovery from the real sample (98.9%), and excellent reproducibility, making it a suitable analytical tool for AD detection at the micromolar level.

Cobalt Oxide Nanorod-Modified GCE as Sensitive Electrodes for Simultaneous Detection of Hydroquinone and Catechol

An electrochemical sensor based on a cobalt oxide nanorod (Co3O4NR) modified glassy carbon electrode (GCE) (Co3O4NR-GCE) was prepared for simultaneous and selective determination of hydroquinone (HQ) and catechol (CT). Surface morphology and crystallinity of Co3O4NR were investigated employing field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) analysis. The structure (16 nm) of the Co3O4 nanorod was observed in the FESEM image. A sharp peak pattern in the XRD survey revealed the following crystal planes in Co3O4NR material: (111), (220), (311), (222), (400), (422), (511), and (440). Electrochemical characterization of modified Co3O4NR-GCE was carried out performing cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Selective and simultaneous detection of HQ and CT was carried out by performing CV and differential pulse voltammetry (DPV) analysis. In both studies, modified Co3O4NR-GCE showed well defined oxidation and reduction peaks for HQ and CT with enhanced peak current, and the oxidation peaks for HQ and CT were observed at 0.152 V and 0.254 V, respectively, in the CV analysis. Scan rate and pH variation analysis were performed to evaluate different kinetic parameters, including charge transfer coefficient (α = 0.56 for HQ and 0.66 for CT), heterogeneous charge transfer rate constant (ks = 56 for HQ and 72 for CT), and the number of electrons involved in HQ and CT oxidation. Quantitative analysis of HQ and CT was studied by observing the current response of DPV analysis with respect to concentration variation. Here, the detection limit was calculated as 0.2 µM for HQ with a linear concentration range of 5–200 µM, and 0.4 µM for CT with a linear concentration range of 5–150 µM. The practical applicability of the proposed sensor was investigated using sample solutions prepared in tap water. The reported sensor showed impressive selectivity towards HQ and CT in the presence of common interferents.

Electrochemical Sensors Based on Conducting Polymers for the Aqueous Detection of Biologically Relevant Molecules

Electrochemical sensors appear as low-cost, rapid, easy to use, and in situ devices for determination of diverse analytes in a liquid solution. In that context, conducting polymers are much-explored sensor building materials because of their semiconductivity, structural versatility, multiple synthetic pathways, and stability in environmental conditions. In this state-of-the-art review, synthetic processes, morphological characterization, and nanostructure formation are analyzed for relevant literature about electrochemical sensors based on conducting polymers for the determination of molecules that (i) have a fundamental role in the human body function regulation, and (ii) are considered as water emergent pollutants. Special focus is put on the different types of micro- and nanostructures generated for the polymer itself or the combination with different materials in a composite, and how the rough morphology of the conducting polymers based electrochemical sensors affect their limit of detection. Polypyrroles, polyanilines, and polythiophenes appear as the most recurrent conducting polymers for the construction of electrochemical sensors. These conducting polymers are usually built starting from bifunctional precursor monomers resulting in linear and branched polymer structures; however, opportunities for sensitivity enhancement in electrochemical sensors have been recently reported by using conjugated microporous polymers synthesized from multifunctional monomers.

Sensitive and Simultaneous Determination of Hydroquinone and Catechol in Water Using an Anodized Glassy Carbon Electrode with Polymerized 2-(Phenylazo) Chromotropic Acid

Hydroquinone (HQ) and catechol (CT) are considered as environmental pollutants with high toxicity. We have developed a simple electrochemical sensor using an anodized glassy carbon electrode modified with a stable 2-(phenylazo) chromotropic acid- (CH-) conducting polymer (PCH/AGCE). The PCH/AGCE sensor showed good electrocatalytic activity and reversibility towards the redox of HQ and CT in phosphate buffer solution (PBS, pH 7.0). The cyclic voltammetry (CV) in mixed solution of HQ and CT showed that the oxidation peaks of them became well resolved with a peak separation of 0.1 V. The detection limits of HQ and CT were 0.044 and 0.066 μM, respectively, in a wide linear response range of 1–300 μM for both. Moreover, the sensor displayed an excellent selectivity in the presence of common interferences. This study provided a simple, sensitive, and high recovery method for simultaneous and quantitative determination of HQ and CT in aqueous medium.

Simultaneous voltammetric determination of hydroquinone and catechol by using a glassy carbon electrode modified with a ternary nanocomposite prepared from oxidized multiwalled carbon nanotubes, manganese dioxide and manganese ferrite

An electrochemical sensor is described for simultaneous determination of hydroquinone (HQ) and catechol (CT) via differential pulse voltammetry (DPV). It is making use of a ternary composite material prepared from oxidized multiwalled carbon nanotubes, manganese dioxide (MnO₂) and manganese ferrite (MnFe₂O₄). The material was obtained by a one-step hydrothermal reaction and used to modify a glassy carbon electrode (GCE). The composite was characterized by Fourier transform infrared spectroscopy, X-ray powder diffraction, thermogravimetric analysis, X-ray photoelectron spectroscopy and scanning electron microscopy. The peak currents for HQ and CT are highest at 172 and 276 mV (vs. Ag/AgCl) at a pH value of 6.0. Response increases linearly in the 1-400 μM HQ and CT concentration ranges, and the detection limits are 0.64 and 0.48 μM, respectively. The modified GCE is highly selective, repeatable and reproducible. A single sensor was used to make 23 subsequent measurements, and the relative standard deviations were 1.8% and 2.3% for HQ and CT, respectively. Graphical abstract Schematic representation of the preparation of ternary nanocomposite and its electrochemical behavior towards hydroquinone and catechol.

Synergistic effect of a cobalt fluoroporphyrin and graphene oxide on the simultaneous voltammetric determination of catechol and hydroquinone

Graphene oxide (GO) was modified with the cobalt(II) and zinc(II) complexes (CoTFPP and ZnTFPP) of 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin in order to improve the electrocatalytic activity of GO towards catechol (CC) and hydroquinone (HQ). It is found that the CoTFPP-modified GO on a glassy carbon electrode (GCE) displays the highest electrocatalytic activity. The response to CC (at 0.14 V vs. SCE) is linear in the 1-220 μM concentration range. The response to HQ (at 0.04 V vs. SCE) extends from 1 μM to 200 μM. The sensitivity and detection limits are 10.40 μA∙μM^-1∙cm^-2 and 0.17 μM for CC, and 8.40 μA∙μM^-1∙cm^-2 and 0.21 μM for HQ. Experimental results indicate that the Co(II) and Zn(II) ions in the porphyrins positively affect the electron transfer rate in the hybrid materials. The GCE modified with CoTFPP/GO was successfully applied to the simultaneous determination of CC and HQ in spiked samples of tap and lake water. Graphical abstract Schematic presentation of a voltammetric method for simultaneous determination of catechol (CC) and hydroquinone (HQ). It is based on the use of a cobalt (II) fluoroporphyrin (CoTFPP) functionalized graphene oxide (GO) hybrid.