Paraffin-impregnated Graphite Electrode Research Articles

Synthesis, characterisation and voltammetric study of dimethylammonium lead iodide perovskite

In the last decade, the most investigated perovskite materials are the hybrid organic-inorganic perovskites (HOIPs) due to their optoelectronic properties and possible application in the production of photovoltaics. This interest has led to an ongoing search for new HOIP variants, alongside thorough investigations of the properties of existing HOIPs. That is why our research in the field of organic-inorganic perovskites is aimed at the synthesis, characterization, and investigation of the electrochemical properties of dimethylammonium lead iodide (DMAPbI3) using voltammetric studies. A modified synthesis of DMAPbI3, differing slightly from the one described in the literature, was performed by combining stoichiometric amounts of lead iodide (PbI2) and dimethylammonium iodide (DMAI) dissolved in acetonitrile. After conducting controlled evaporation, a yellow crystalline powder of DMAPbI3 was obtained. The identity and purity of the obtained compound were confirmed by powder X-ray diffraction (PXRD), infrared (IR) and Raman spectroscopy, and scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX). Investigations on the electrochemical properties of DMAPbI3 by cyclic voltammetry were performed with dichloromethane (DCM) and tetrabutylammonium chloride (TBAC) as the electrolyte. A paraffin-impregnated graphite electrode (PIGE) was used as a working electrode, on which the perovskite microparticles were immobilized. The electrochemical activity of DMAPbI3 is recognized through an intense, broad, and irreversible anodic peak attributed to the oxidation of the constituents to different possible products and the decomposition of the perovskite structure.

Determination of Individual Gibbs Energies of Ion and Electron Transfer in Electrochemical Insertion Processes

Based on three-phase electrode models, we study to access the Gibbs energy contributions for the transfer of ions and electrons in Prussian blue analogs since they have long life cycles and high energy efficiency. Ni[Fe(CN)6] (HCFNi) and Cu[Fe(CN)6] (HCFCu) were preliminarily synthesized by a hydrothermal process. The obtained HCFNi powders were supported on a paraffin-impregnated graphite electrode in contact with an organic electrolyte, producing solid-state oxidation-reduction electrochemical reactions, which have been monitored by cyclic voltammetry and open circuit potential measurements in the presence of potassium as intercalating ion. The results show a behavior according to the Nernst equation as the potassium ion concentration varies, with a slope of 61.2 mV/dec. These experiments make it possible to access Gibbs free energy values for both transfers separately and replicate them for different insertion ions, such as Na+ and Li+.Figure: (Left) Open circuit potential measurements; (center) mid-peak potential measurements; and (right) cyclic voltammetry for Ni[Fe(CN)6] in potassium media. Figure 1

Electrochemical Estimations of the Gold Nanoparticle Size Effect on Cysteine-Gold Oxidation

Gold nanoparticles are interesting for nanobiomedical applications, such as for drug delivery and as diagnostic imaging contrast agents. However, their stability and reactivity in-vivo are influenced by their surface properties and size. Here, we investigate the electrochemical oxidation of differently sized citrate-coated gold nanoparticles in the presence and absence of L-cysteine, a thiol-containing amino acid with high binding affinity to gold. We found that smaller sized (5, 10 nm) gold nanoparticles were significantly more susceptible to electrochemical L-cysteine interactions and/or L-cysteine-facilitated gold oxidation than larger (20, 50 nm) sized gold nanoparticles, both for the same mass and nominal surface area, under the conditions investigated (pH 7.4, room temperature, stagnant solutions, and scan rates of 0.5 to 450 mV s−1). The electrochemical measurements of drop-casted gold nanoparticle suspensions on paraffin-impregnated graphite electrodes were susceptible to the quality of the electrode. Increased cycling resulted in irreversible oxidation and detachment/oxidation of gold into solution. Our results suggest that L-cysteine-gold interactions are stronger for smaller nanoparticles.

Electrochemical behavior of 5-type phosphodiesterase inhibitory drugs in solid state by voltammetry of immobilized microparticles

Evaluation of electrochemical behavior of 5-type phosphodiesterase inhibitory drugs is of major concern since they have been added illegally as adulterants in dietary supplements. Then, for the first time, the solid-sate electrochemistry of sildenafil and tadalafil is described using voltammetry of immobilized microparticles (VIMP). An electrochemical cell was designed and printed in a fused deposition modeling (FDM)-based 3D printer for VIMP measurements. The 3D-printed cell designed with a distance of 5 mm between the working and reference electrode presented better voltammetric response and decrease in the uncompensated resistance of the electrochemical system. Cyclic and square wave voltammograms of the individual compounds were recorded in a paraffin-impregnated graphite electrode in contact with 0.01 mol L−1 H2SO4. The electrochemical oxidation/reduction products were characterized by Raman spectroscopy and scanning electron microscopy (SEM). Different voltammetric responses were detected for the solid compounds depending on the solubility of the parent compound and their products of oxidation/reduction. Moreover, significant crystal re-structuring was also observed after voltammetric scan of the solid compounds. Under optimized conditions, sildenafil and tadalafil could be electrochemical identified and distinguished in dietary supplements.

Determination of gallic acid using poly(glutamic acid): graphene modified electrode

Gallic acid (GA) is one of the main phenolic components occurring naturally in plants and has been a subject of increasing interest owing to its antioxidant, anti-mutagenic and anti-carcinogenic properties. The present work describes a rapid and cost-effective analytical procedure for the determination of gallic acid. Poly-Glu/rGO electrode was fabricated by the electro-polymerisation of glutamic acid on reduced graphene oxide (rGO) modified paraffin impregnated graphite electrode (PIGE). The modified electrode was characterized by SEM, AFM and ATR-IR. The electrochemical behavior of gallic acid at the modified sensor was studied by voltammetric and amperometric techniques under optimized conditions in pH 5 acetate buffer. The electrode showed good linear response towards the determination of gallic acid over the range of 0.03–480 $$\upmu {\hbox {M}}$$ with 0.01 $$\upmu \hbox {M}$$ as the detection limit for voltammetric technique and the amperometric technique showed a linear range of 1–17 $$\upmu \hbox {M}$$ with 0.33 $$\upmu \hbox {M}$$ as the detection limit. The electrode also showed good stability and reproducibility with a sensitivity of 0.97 $$\upmu \hbox {M}$$ / $$\upmu $$ A. The proposed method can be applied to detect GA in real samples with satisfactory results. SYNOPSIS This work describes a rapid and cost-effective analytical procedure for the determination of gallic acid. Poly-Glu/rGO electrode was fabricated by electro-polymerisation of glutamic acid on reduced graphene oxide (rGO) modified paraffin impregnated graphite electrode (PIGE). The electrode showed linear response towards gallic acid over the range of 0.03–480 $$\upmu \hbox {M}$$ with 0.01 $$\upmu \hbox {M}$$ as the detection limit for voltammetric technique and a linear range of 1–17 $$\upmu \hbox {M}$$ with 0.33 $$\upmu \hbox {M}$$ as the detection limit for amperometric technique. The proposed electrochemical sensor can be applied to detect GA in real samples with satisfactory results.

Study of Electrochemical Behaviour of Carotenoids in Aqueous Media

AbstractFocus of this research was electrochemical study of β‐carotene, astaxanthin and lutein in aqueous media. Compounds were investigated on paraffin impregnated graphite electrode (PIGE) in 0.1 M HClO4 aqueous electrolyte using square‐wave voltammetry (SWV) with pulse amplitude of 50 mV and step potential of 2 mV.Voltammetry of immobilized microparticles (VIM) allowed determination of β‐carotene and astaxanthin as solids immersed in aqueous electrolyte. Results obtained with SWV revealed oxidation peaks at 0.88 V and 1.09 V versus Ag/AgCl for β‐carotene and astaxanthin, respectively. To obtain additional information about their behaviour, stripping voltammetry microprobe (SPV) was employed. With this technique the responses of astaxanthin, β‐carotene and lutein exhibit three peaks (−0.345 V, 0.47 V and 0.65 V), two peaks (0.477 V and 0.725 V) and a single peak at 0.687 V, respectively. Based on these results, antioxidant activity of these carotenoids is in order: astaxanthin > β‐carotene > lutein. Good dose‐response relationship between carotenoid concentrations precipitated on PIGE and net peak current was obtained, but in rather narrow concentration range for each compound.

Anodic stripping voltammetric determination of Hg(II) using poly xylenol orange film modified electrode

A sensitive determination of Hg(II) in different water samples has been carried out using stripping voltammetric technique based on poly xylenol orange film modified electrode. The modified poly xylenol orange (PXO) film was fabricated on the paraffin-impregnated graphite electrode (PIGE) using electro polymerization method by applying the potential between − 0.4 V to 0.8 V at a scan rate of 50 mV/s for 30 segments in 0.1 M phosphate buffer solution (pH 7.0) containing 5 × 10−4 M of xylenol orange. The PXO film modified electrode was characterized by DRS-UV, SEM, and differential pulse voltammetry techniques. The xylenol orange film electrode was used to preconcentrate Hg(II) ions through complexation; the complexed metal ions were then reduced electrochemically followed by stripping anodically from the surface of the modified electrode. The obtained linear concentration range for Hg(II) was from 0.13 to 20.5 μg/L with a limit of detection is 0.043 μg/L.

Electrochemical Characteristics of 4‐oxo‐4H‐pyran‐dicarboxylic Acid (Chelidonic Acid) and some of its Metal Complexes

AbstractA few novel metal complexes of chelidonic acid (chelH2), namely [Ca(chel)(H2O)3] (1), [Cu(chel)(H2O)5] ⋅ 2H2O (2) and [VO(chel)(H2O)3] ⋅ 2H2O (3) were prepared, identified by elemental analysis and characterized by electrochemical methods. IR‐spectra and thermal stability in solid state are discussed as well. The electrochemical characteristics of the free chelidonic acid and its complexes 1–3 were studied by (cyclic) square‐wave voltammetry, on static mercury drop electrode (SMDE) and paraffin‐impregnated graphite electrode (PIGE), in aqueous media over a wide pH range. The reduction of chelidonic acid on SMDE is a kinetically controlled electrode reaction, occurring with the transfer of one electron and two protons for 1<pH<6, whereas in very alkaline media the electron transfer is pH independent, i.e. the mechanism of electro‐reduction of chelH2 is proposed. The experimental parameters of the electroanalytical procedure were optimized and the method was applied for the investigation of the metal ion coordination preferences toward chelidonic acid. For the direct determination of solid complexes 1–3, SW voltammetry of microparticles was used.

Electrochemistry-based determination of pungency level of hot peppers using the voltammetry of microparticles

The electrochemical behaviour of capsaicin on a paraffin-impregnated graphite electrode (PIGE) was investigated using square-wave (SWV) and cyclic voltammetry (CV) in a wide range of pH values (2.0–11.0) and potential scan rates. The electrochemical oxidation of capsaicin is an irreversible process and occurs in a complex, pH dependent mechanism. In electrolytes with 2≤pH≤10 oxidation involves the transfer of two electrons and two protons, followed by chemical transformation and the formation of a product which undergoes a further reversible redox reaction. However, at pH close to pKa the product of two-electron electrochemical oxidation of capsaicin dissolves into the electrolyte.Analysis of microparticles of dry ground pepper samples immobilized on the surface of PIGE was performed using SWV under optimal experimental conditions of pH 11, pulse amplitude of 50mV, frequency of 150Hz, and step potential of 2mV. The presence of capsaicin in samples was registered with good precision and sensitivity. The proposed methodology exploits the current intensity of capsaicinoids in pepper samples in order to classify samples according to their pungency. A strong positive correlation was observed between the measured peak currents for capsaicinoids in pepper samples and the average of Scoville heat units reported in the literature (R=91.3%).

Application of different types of carbon nanotubes as PIGE surface modifier in Pd(II) electrochemical determination

ABSTRACTNowadays, carbon nanotubes with differences in specific surface area, dopants, or functional groups are used in a number of applications, electrolysis not excluding. Various types of carbon nanotubes could improve bare graphite electrode properties by different way and so result in obtaining the different records for the same analyte. The automobile catalysts represent mobile sources of palladium. Levels of palladium in environment are continuously increasing and they need to be monitored. Electrochemistry is a useful and inexpensive component of the field of environment monitoring. For Pd(II) electrochemical determination, six types of carbon nanotubes were used as paraffin impregnated graphite electrode (PIGE) surface modifiers. Voltammetric determination brought interesting results of LOD, LOQ, standard and relative precisions of the method. These parameters as well as prediction intervals were calculated according to the technical procedure DIN 32 645 for the six electrodes and three pH values. Modification of PIGE with nitrogen doped carbon nanotubes (LOD = 1.91 × 10−5 mol L−1 or 3.14 × 10−5 mol L−1 for pH 3 and pH 4.5, respectively) seems very promising. In laboratory, functionalized carbon nanotubes, with specific surface area 200 m2 g−1, provided LOD = 1.49 × 10−5 mol L−1 (pH = 3) and 1.42 × 10−5 mol L−1 (pH = 4.5)

CuO Nanofibers Immobilized on Paraffin-Impregnated Graphite Electrode and its Application in the Amperometric Detection of Glucose

1-D nanostructures are promising materials for development of electrochemical devices offering benefits such as fast electron transfer rates and large surface areas. Copper oxide nanofibers (CuO-NFs) synthesized by electrospinning technique and subsequent thermal treatment, were used to modify paraffin-impregnated graphite electrode (PIGE) for a sensitive non-enzymatic glucose detection. The structure and morphology of CuO-NFs were characterized by scanning electron microscopy and transmission electron microscopy. The electrocatalytic activity towards glucose oxidation was evaluated by cyclic voltammetry and chronoamperometry. The results reveal a wide linear response to glucose ranging from 1.0 × 10-6 to 1.93 × 10-3mol L-1 (R2 = 0.9927). The limit of detection was 0.39 × 10-6 mol L-1 (LOD = 3σ/s). The high aspect ratio of the nanofibers arranged in a three-dimensional network structure significantly enhances the electron transfer process. The electrode preparation is simple and rapid execution, and more importantly the graphite rod is relative low-cost and easy to achieve surface renewal for reusability.

Performance Characteristics of Modified Paraffin Impregnated Graphite Electrodes—Testing of Different Carbon Nanotubes Binders

The electrochemical properties of modified paraffin impregnated graphite electrodes (PIGEs) were tested throughout an electrochemical determination of Cu(II). The PIGEs were modified either by casting of carbon nanotubes suspension on prepared electrode surface or its abrasive deposition was used. Ten types of PIGE-modified electrodes, differed in type of dispersing agent used for CNT treatment and manner of modification, were evaluated. Chemometric characteristics of measurements were calculated and compared.

Electrochemical mediated preparation of chelating polymer brushes at paraffin-impregnated graphite electrode for Pb2+ sensing

In this work, two-dimension iminodiacetic acid functional gclycidyl methacrylate polymer brushes were prepared at paraffin-impregnated electrode for Pb2+ sensing. Gclycidyl methacrylate polymer brushes were prepared using electrochemical mediated atom transfer radical polymerization, ring-opening reaction of the epoxy groups was enforced using iminodiacetic acid to form chelating polymer brushes (IGMA/WGE). The electrode was carefully examined by fourier transform infrared spectroscopy, field emission scanning electronmicroscope and electrochemistry techniques. Abundant chelating polymer brushes evenly coated at WGE with an average size of 0.1×2μm. Further IGMA/WGE was successfully used for the determination of Pb2+ by differential pulse adsorptive anodic stripping voltammetry. The current responses (-0.58V) were linearly increased depending on the concentration from 3 to 90nM (i(μA)=-1.12+0.82 c (nM), limit 0.79nM, 3σ). The present electrode is potentially useful for real sample analysis.

Electrochemical characterization of bronze historical objects using voltammetry of microparticles

This work presents the application of voltammetry of microparticles (VMP) to the characterization of metallic artefacts. The paper illustrates the principle of the technique and the methods for the identification of metals and copper minerals. VMP can be considered a non-invasive technique as it requires a minimum amount of material for performing the analyses. To emphasize the efficacy of this technique regarding characterization of cultural heritage materials, two bronze artefacts of different historical periods were investigated. By using a paraffin-impregnated graphite electrode, the composition of the alloy and the copper minerals present in their patinas were analysed and identified. The results obtained from the electrochemical characterization were confirmed by complementary analysis carried out with X-ray fluorescence and X-ray diffraction.

TOF-SIMS surface analysis of L-Tryptophan self assembled monolayer

Abstract This paper dealt with the preparation and characterization of self — assembled monolayersSAM-s of 1-hexadecanethiole and mercapto acetic acid on the silver nanostructure and subsequently the immobilization with amino acid L-Tryptophane. In order to achieve it, we used the electrodeposition of silver onto nanostructured surface of paraffin impregnated graphite electrode (PIGE). Subsequently, we assembled SAM by choosing the 1-hexadecanethiole and mercaptoacetic acid. These two kinds of SAM underwent the functionalization by L-Tryptophan. The observations of silver on PIGE surfaces were performed by scanning electron microscope (SEM). For surface analysis of the SAM functionalized by L-tryphophan, the TOF-SIMS technique was chosen. Finally, the fragmented ions of the immobilized-L-Tryptophan SAM were determined on the basis of suggested residues and three-dimensional structure. The residues show that the ability of L-Tryptophan to build homogeneous structure is better by mercaptoacetic acid SAM structure than by 1-hexadecanethiol. It was observed that L-Tryptophan built compact surface, which, due its chemical properties, can represent very interesting side regarding biocompatibility, homochirality and robustness in the area of life science.

Ultrasonic preparation of tetraoxalyl ethylenediamine melamine resin-coated multiwalled carbon nanotubes for trace Ni(II) sensing

Under an aid of ultrasonic, tetraoxalyl ethylenediamine melamine resin-coated multiwalled carbon nanotubes were prepared for Ni(II) sensing in aqueous solution. The processes involved the fabrication of tetraoxalyl ethylenediamine melamine resin by one pot way, the coating of tetraoxalyl ethylenediamine melamine resin at multiwalled carbon nanotubes (MWCNTs), and the determination of Ni(II). The present materials were carefully examined by Fourier transform infrared spectroscopy, field emission scanning electron microscope, and electrochemistry techniques. A great deal of amorphous microsphere could be observed for tetraoxalyl ethylenediamine melamine resin with an average diameter of 1.2 μm, and MTE could evenly adhere at the surface of MWCNTs by the ultrasonic. Tetraoxalyl ethylenediamine melamine resin-coated multiwalled carbon nanotube-modified paraffin-impregnated graphite electrode was successfully used for the determination of Ni(II) by differential pulse adsorptive anodic stripping voltammetry. The current responses (−0.3 V) were linearly increased depending on the concentration from 1 × 10−11 to 3 × 10−10 M (i (μA) = 11.1 + 7.9 c (1 × 10−12 M); R = 0.9901, 3σ = 7 × 10−12 M).

Anodic dissolution of iron microparticles in chloride-containing acetate buffer electrolytes studied by elimination voltammetry

Elimination voltammetry with linear scan (EVLS) was used for the study of the anodic dissolution process of iron microparticles immobilized on paraffin-impregnated graphite electrode. This process was investigated in acetate buffer solutions in the range of pH 4 to 6 and the effect of chloride ions was evaluated. It was found that the anodic dissolution process of iron powder proceeded in two peaks with different pH and KCl-dependent characterizations. Both the more negative process at about �300 mV and the positive process at about 1,200 mV are influenced by chlo- ride and hydroxyl ions. Chloride ions incorporate into the intermediate species and form more soluble species in the passivation layer, leading to its degradation. Detailed infor- mation about the processes was provided by the EVLS functions conserving diffusion current components. The mechanism of anodic dissolution of iron powder in acetate solutions representing passive ions and chloride ions appearing in the role of corrosion activators was discussed.

Square‐Wave Voltammetry of Sodium Copper Chlorophyllin on Glassy‐Carbon and Paraffin‐Impregnated Graphite Electrode

AbstractElectrochemical oxidation of sodium copper chlorophyllin (CHL) has been investigated at a glassy‐carbon (GC) and paraffin‐impregnated graphite electrode (PIGE) using square‐wave voltammetry (SWV). Square‐wave voltammograms of other two chlorin‐type compounds, namely chlorin e6 and chlorophyll a, have been studied as well. The measurements were performed in the pH range between 7 and 11. The square‐wave frequency was changed between 8 and 1000 Hz. The oxidation of studied chlorins is a complex, pH‐independent, reversible or quasireversible process, followed by the chemical transformation of the product. The product of the EC reaction of CHL is an electroactive ππ dimer, which strongly adsorbs on the electrode surface and undergoes further oxidation at more positive potential. The electrooxidation of the adsorbed dimer is a pH‐independent irreversible process with the formation of an electroinactive film. The voltammetric behaviour of chlorin e6 on PIGE was qualitatively similar to that of CHL. The SW voltammograms of chlorin e6 recorded on GCE and of chlorophyll a recorded on PIGE consisted of only one peak. The SW responses of studied compounds strongly depend on the stabilization of the reaction intermediate by adsorption to the electrode surface.

Potential Application of Voltammetry of Microparticles for Dating Porcine Blood‐based Binding Media used in Taiwanese Architectural Polychromies

A method for dating Hemoglobine-containing archaeological samples using the voltammetry of microparticles is described. This is based on the record of the voltammetric response of such materials attached to paraffin-impregnated graphite electrodes in contact with aqueous acetate buffer. Signals attributable to the Fe(III)/Fe(II) iron couple and their catalytic enhancement in the presence of H(2)O(2) can be correlated, via first-order reaction kinetics, with the time of aging of the samples. The method has been applied to the study and dating of the polychromed architectural decoration of different parts of the architectural complex of the Longshan Temple in Lukang (18(th) century, Taiwan).

Mapping of corrosion products of highly altered archeological iron using voltammetry of microparticles

The application of the voltammetry of microparticles to identify corrosion products on different localizations of highly altered archeological iron pieces is described. The use of graphite pencil methodology permits to mapping different corrosion products, namely, akaganeite, goethite, hematite, jarosite, magnetite, maghemite and siderite, in iron artifacts. Identification protocols are based on square wave voltammetric measurements performed at sample-modified paraffin-impregnated graphite electrodes immersed into aqueous HCl. This methodology is applied for mapping corrosion products on an Iberian–Roman shield boss from the Torre la Sal archeological site (Oropesa, Spain) dated in the IVth century BC.