Electroanalytical Measurements Research Articles

Investigation of the effects of uranium(III)-chloride concentration on voltammetry in molten LiCl-KCl eutectic with a glass sealed tungsten electrode

One of the major sources of error for electroanalytical measurements in high-temperature molten salts is from the measurement of the working electrode (WE) area. A glass sealed working electrode (GSWE) was developed in order to set the exposed area of tungsten and reduce the error associated with WE area. The insulating property of the glass while in contact with molten salt was verified by observing the independence of electrochemical signals with adjustments in the WE position. The integrity of the glass coating was also confirmed by observing the stability of electrochemical signals (±1.9%) over several hours. Cyclic voltammetry (CV) and normal pulse voltammetry (NPV) were applied at 10 different concentrations of UCl3. Above 0.17moldm−3 UCl3, the electrochemical signals from CV and NPV deviate significantly from linearity with concentration, but in opposite directions. A shift from reversible to quasi-reversible behavior and migration are theorized to cause the non-linearity for CV and NPV, respectively. A model is proposed to account for migration in NPV resulting in a significant error reduction in the electrochemical concentration measurement.

Single Drop Electroanalysis and Interfacial Interactions: Sensitivity versus Limit of Detection†.

We report single drop electroanalytical measurements of pharmaceutically and biologically relevant compounds using screen printed electrodes (SPEs) modified with carboxylated multiwalled carbon nanotubes (MWCNT-COOH) as the sensor surface. Acetaminophen, nicotine, ascorbic acid, and nicotinamide adenine dinucleotide reduced form (NADH) were detected in a single drop of solution. We show that combined polar and nonpolar interactions of analytes with -COOH functional groups and large surface area of MWCNT, respectively, allow highly sensitive analyte detection with wide dynamic range. Smaller analytes can bind to a significantly greater number of sensor sites than the bulkier analytes and offer better detection sensitivity. Results suggest that sensitivity is controlled by predominant nonpolar interactions that an analyte can undergo with the MWCNT-COOH SPE sensor surface, whereas limit of detection is controlled by the extent of polar interactions between an analyte and the sensor surface, facilitating interfacial charge transport and an electrochemical signal output. Furthermore, a combination of polar and nonpolar analyte interactions with the sensor surface shows a synergistic effect on sensitivity and detection limit. This could be a likely reason for why sensitivity does not need to always correlate with lower detection limits as variations in the interfacial interactions are critical. Application of the designed single drop method to real samples was validated by estimating the amounts of acetaminophen, nicotine, ascorbic acid, and NADH in commercially available pharmaceuticals with excellent recovery.

Redox Cycling in Nanopore-Confined Recessed Dual-Ring Electrode Arrays

A redox cycling geometry based on an array of nanopore-confined recessed dual-ring electrodes (RDREs) has been devised to amplify electrochemical signals and enhance the sensitivity of electroanalytical measurements. The RDRE arrays were fabricated using layer-by-layer deposition followed by focused ion beam milling. A characteristic feature of the nanoscale dual-ring geometry is that electrochemical reactions occurring at the bottom-ring electrode can be tuned by modulating the potential at the top-ring electrode. Thus, the resulting device was operated in generator–collector mode by holding the top-ring electrodes at a constant potential and performing cyclic voltammetry by sweeping the bottom-ring potential in aqueous Fe(CN)63–/4–. The enhanced (∼23×) limiting current, achieved by cycling the redox couple between top- and bottom-ring electrodes with high collection efficiency, was compared with that obtained in the absence of self-induced redox cycling (SIRC). Measured shifts in Fe(CN)63–/4– concentrat...

Density functional treatment and electro analytical measurements of liquid phase interaction of 2-ethylbenzimidazole (EBI) and ethyl (2-ethylbenzimidazolyl) acetate (EEBA) on mild steel in hydrochloric acid

DFT calculations on the liquid phase interaction and corrosion inhibition properties of 2-ethylbenzimidazole (EBI) and its derivative ethyl (2-ethylbenzimidazolyl)acetate (EEBA) on mild steel in hydrochloric acid (0.5, 5 and 1.5M) at three different temperatures (303, 308 and 313K) have been studied using EIS, polarization, adsorption measurements and computational calculations. Results show that EBI and EEBA act as effective inhibitors for the corrosion of mild steel in hydrochloric acid media. Polarization studies showed that both the inhibitors behave as mixed type inhibitors with respect to the electrode reactions. EEBA offers better inhibition efficiency than EBI. The inhibition efficiency found to decrease with increase in temperature in either of the cases. The mechanism involves adsorption phenomenon and in the case of EEBA, the adsorption obeyed Langmuir adsorption isotherm. For EBI, the adsorption obeyed Langmuir adsorption isotherm except for 313K in 1.5M HCl, for which the best fit adsorption isotherm was Temkin adsorption isotherm.

A highly sensitive electrochemical determination of norepinephrine using l-cysteine self-assembled monolayers over gold nanoparticles/multi-walled carbon nanotubes electrode in the presence of sodium dodecyl sulfate

A novel electrochemical sensor consisting of l-cysteine self-assembled monolayers over gold nanoparticles/multi-walled carbon nanotubes modified glassy carbon electrode (l-Cys/AuNPs/MWCNTs/GCE) was fabricated and applied for the determination of norepinephrine (NE) in the presence of sodium dodecyl sulfate (SDS) for the first time. Electroanalytical measurements including cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used. The optimum buffer of pH 5.0 contained 30μM SDS, the NE oxidation peak current enhanced linearly with concentration ranging from 0.2 to 100μM (R2 of 0.9998) with a detection limit of 0.03μM. In the presence of SDS, the modified l-Cys/AuNPs/MWCNTs/GCE electrode showed high selectivity for the detection of NE in the presence of ascorbic acid and uric acid. High recoveries in the range of 80.7–100.2% were obtained in spiked human serum samples. Our modified electrode displayed a high reproducibility, sensitivity and long term stability.

Nanostructure Restoration of Thermally Reduced Graphene Oxide Electrode upon Incorporation of Nafion for Detection of Trace Heavy Metals in Aqueous Solution

AbstractHigh performance reduced graphene oxide (RGO)‐Nafion (N) thin film electrodes coated on silicon (Si) substrates (RGO‐N/Si) were successfully developed through thermal reduction of GO‐N without delamination from the substrates. The restoration of the RGO‐N nanostructure upon the addition of Nafion was proven by Raman spectroscopy (RS) and field emission scanning electron microscopy, and the restoration mechanism of the RGO‐N nanostructure was proposed. Through the investigation using x‐ray photoelectron spectroscopy (XPS), the polyfluorocarbon from Nafion possessed a function that could prevent the delamination of the RGO sheets from the substrates during the thermal reduction. The RGO‐N/Si samples were later used for the determination of trace heavy metals, such as divalent lead, cadmium and copper ions (Pb2+, Cd2+ and Cu2+, respectively) using square wave anodic stripping voltammetry in a 0.1 M acetate buffer solution (pH 5). Based on the electroanalytical measurements, the RGO‐N/Si samples exhibited a highly linear behavior in the detection of Cd2+, Pb2+ and Cu2+ over the concentration range of 50 nM to 300 nM with detection limits at nM levels. In addition, the RGO‐N/Si samples presented good recoveries of target metals in tap water samples.

Color Tests and Electrocanalytical Methods for the Preliminary Identification of Drugs

In the literature various chemical reagents have been developed during the past century that are suitable for the preliminary identification of different illicit drugs such as Marquis, Liebermann’s, Simon’s. Color tests are an important tool for the preliminary identification of illicit drugs in spite of developments in instrumental technology and the increased portability of this technology which enables its use in the field. Color tests or spot tests are chemical tests that involve the reaction of a sample with a reagent or a series of reagents to produce a color or a change in color. The popularity of color tests arises from the fact that they are generally simple, quick, inexpensive, and quite sensitive. They are readily available and require minimal materials. These factors enable color tests to be used in the field and can be employed by those without extensive chemical backgrounds. A negative result for a color test is helpful, for instant in excluding a drug or class of drugs, depending on the test performed. In this study, we are going to describe a concept of utilization of various Keggin-type heteropolyacids of molybdenum and tungsten as suitable reagents for the preliminary identification of suspected illicit drug samples. Heteropolyacids of molybdenum and tungsten will be used as solution (spot test) as well as strip test for the screen identification of illicit drug samples. Moreover, the electroanalytical diagnostic experiments and ATR-FTIR measurements have been also utilized for identification of various illicit drugs.

Carbon Nanotube Photoluminescence for Bioelectroanalytical Measurements

The intrinsic near-infrared photoluminescence of semiconducting single-walled carbon nanotubes exhibits environmental sensitivity which has been employed to detect various analytes in complex environments, including biological media. To build biomedical technologies that employ carbon nanotube photoluminescence, a better understanding of the optical response, as well as new methods to measure it in biological systems, are needed. We have developed new imaging platforms to quantify nanotube emission, including a method to conduct photoluminescence excitation/emission spectroscopy on living samples. We are also exploring ionic screening phenomena during ambient pseudocapacitive charging as a modulator of nanotube photoluminescence for electroanalytical measurements in biological media.

Electroanalytical Measurements of Binary-Analyte Mixtures in Molten LiCl-KCl Eutectic: Gadolinium(III)- and Lanthanum(III)-Chloride

Electroanalytical measurements, such as cyclic voltammetry and chronopotentiometry, have been applied by other researchers to many eutectic LiCl-KCl mixtures containing a single analyte, typically a rare earth or actinide ion. These measurements have demonstrated the applicability of electroanalytical measurements of concentration in molten LiCl-KCl eutectic, which is prevalently used as an electrolyte in the electrorefining of used nuclear fuel (UNF). However, UNF electrorefiners contain multiple actinide and rare earth ions, necessitating the ability to make electroanalytical measurements in multi-analyte mixtures. The presence of multiple analytes creates interferences and overlapping signals. Chronoamperometry, cyclic voltammetry (CV), chronopotentiometry and open-circuit potential measurements were performed in eutectic LiCl-KCl mixtures containing a range of GdCl3 and LaCl3 concentrations to explore the issues associated with applying electroanalytical techniques in multi-analyte molten salt mixtures and to develop possible solutions. CV was found to be most promising for separating and analyzing each ion's signal. CV measurements were semi-differentiated and correlated to concentration using peak heights and principal component regression (PCR) to determine the concentration from electrochemical signals. The lowest average relative error was obtained using PCR for Gd3+ (6.21%) and using peak height correlations for La3+ (10.4%).

Nanopore-enabled electrode arrays and ensembles

This review (with 116 refs.) addresses recent developments in nanoelectrode arrays and ensembles with particular attention to nanopore-enabled arrays and ensembles. Nanoelectrode-based arrays exhibit unique mass transport and ion transfer properties, which can be exploited for electroanalytical measurements with enhanced figures-of-merit with respect to microscale and larger components. Following an introduction into the topic, we cover (a) methods for fabrication of solid-state nanopore electrodes, (b) chemical and biochemical sensors, (c) nanochannel arrays with embedded nanoelectrodes; (d) recessed nanodisk electrode arrays; (e) redox cycling in nanopore electrode arrays, (f) finally discuss novel nanoarrays for electrochemistry, and then give a future outlook. A wide variety of nanoelectrode array-based chemical and biochemical sensors properties are discussed in addition to faradaic, ion transfer and spectroelectrochemical applications.

Reduced graphene oxide decorated with tin nanoparticles through electrodeposition for simultaneous determination of trace heavy metals

Reduced graphene oxide (RGO) decorated with tin nanoparticles (SnNPs) was electrodeposited on glassy carbon sheet (GCS), i.e. G-Sn/GCS, with a drop-casting method followed by constant potential electroreduction. Raman spectroscopic analysis on the graphitic structure of the G-Sn/GCS confirmed a good intercalation of SnNPs in the RGO matrix. Field emission scanning electron microscopic measurements illustrated a uniform distribution of the SnNPs on the RGO sheets. The G-Sn/GCS showed a better electroanalytical performance than the bare GCS and RGO/GCS in the simultaneous determination of divalent cadmium ions (Cd2+), lead ions (Pb2+) and copper ions (Cu2+) using square wave anodic stripping voltammetry. The electroanalytical measurements using the G-Sn/GCS were optimized at −1V for 150s in a 0.1M acetate buffer solution (pH 5). The G-Sn/GCS demonstrated a highly linear behavior in the detection of Cd2+, Pb2+ and Cu2+ in the concentration range of 10nM to 100nM with detection limits of 0.63nM, 0.60nM and 0.52nM (S/N=3), respectively. A mechanism for the formation of the G-Sn nanocomposite was proposed in this paper.

Low-Cost, Fused Filament Fabrication-Prepared, 3D-Printed Microfluidic Devices with Modularly Integrated Electrodes for Electroanalytical Measurements

Decreasing costs, improving availability, and the introduction of new materials for 3D printing technologies have resulted in more extensive applications of 3D printing in chemical and biochemical research. Recently, 3D printing has been used to make microfluidic devices for chemical mixing, gradient generation, and sensing applications, including electrochemical sensing via flow-injection amperometry. While several reports of 3D-printed microfluidic devices have appeared, most of these rely on polyjet, multijet, or stereolithography methods that require expensive printers, costly materials, and/or special finishing and post-processing treatments. Here we show that low-cost, easy-to-prepare microfluidic devices, similar to those that have been reported using more expensive 3D printing methods, can be fabricated using a desktop 3D-printer based on inexpensive fused filament fabrication (FFF). We demonstrate that microfluidic devices with threaded openings can be prepared to enable insertion of 3-electrode fittings in the channel for electroanalytical measurements and applications such as sensing based on flow-injection amperometry. These devices feature channels designed to have width and height dimensions ≤800 μm and are semitransparent to allow visualization of the solution-filled channels. The FFF-printed devices described in this work provide a low-cost, simple alternative to the previously reported modular, 3D-printed systems for flow-injection analysis based on polyjet printing.

Construction of effective disposable biosensors for point of care testing of nitrite

In this paper we aim to demonstrate, as a proof-of-concept, the feasibility of the mass production of effective point of care tests for nitrite quantification in environmental, food and clinical samples. Following our previous work on the development of third generation electrochemical biosensors based on the ammonia forming nitrite reductase (ccNiR), herein we reduced the size of the electrodes' system to a miniaturized format, solved the problem of oxygen interference and performed simple quantification assays in real samples. In particular, carbon paste screen printed electrodes (SPE) were coated with a ccNiR/carbon ink composite homogenized in organic solvents and cured at low temperatures. The biocompatibility of these chemical and thermal treatments was evaluated by cyclic voltammetry showing that the catalytic performance was higher with the combination acetone and a 40°C curing temperature. The successful incorporation of the protein in the carbon ink/solvent composite, while remaining catalytically competent, attests for ccNiR's robustness and suitability for application in screen printed based biosensors.Because the direct electrochemical reduction of molecular oxygen occurs when electroanalytical measurements are performed at the negative potentials required to activate ccNiR (ca.−0.4V vs Ag/AgCl), an oxygen scavenging system based on the coupling of glucose oxidase and catalase activities was successfully used. This enabled the quantification of nitrite in different samples (milk, water, plasma and urine) in a straightforward way and with small error (1–6%). The sensitivity of the biosensor towards nitrite reduction under optimized conditions was 0.55AM−1cm−2 with a linear response range 0.7–370μM.

Morphological Transitions during Au Electrodeposition: From Porous Films to Compact Films and Nanowires

Gold electrodeposition was studied in a sulfite electrolyte to which micromolar concentrations of Tl2SO4 were added. Hysteresis and a regime of negative differential resistance (NDR) evident in electroanalytical measurements are correlated with deposit morphology and interpreted through measurements of thallium underpotential deposition (upd). Deposit morphologies range from specular surfaces to highly faceted dendrite-like grains of moderate aspect ratio and, for potentials within the NDR region, sub-50 nm diameter, high aspect ratio 110 oriented single crystal nanowires. The nanowires exhibit an epitaxial relationship to the substrate that permits one step fabrication of surfaces densely covered with high aspect ratio nanowires having controlled orientations. The NDR and nanowires are a consequence of the non-monotonic relationship between Tl coverage and growth velocity; at low coverage Tl accelerates Au deposition while at higher coverage it inhibits deposition. Immiscibility of the Tl and Au supports on-going surface segregation during area expansion that accompanies nanowire growth leading to greater dilution of the additive coverage and more rapid growth at the nanowire tips, while the sidewalls remain passivated by a saturated Tl coverage.

Bottom-Up Electrodeposition of Zinc in Through Silicon Vias

This paper describes superconformal feature filling during zinc electrodeposition in a sulfate electrolyte. Localized bottom-up filling of Through Silicon Vias (TSVs) with no deposition on the sidewalls or the field around them is demonstrated in electrolytes containing a deposition rate suppressing additive. This behavior is seen when feature filling proceeds at potentials in proximity to where suppression breakdown and localized zinc deposition are noted in electroanalytical measurements with planar rotating disk electrodes. The favorable comparison with previous results for bottom-up feature filling of Cu, Au and Ni further demonstrates the central role of additive-derived negative differential resistance (NDR) in extreme bottom-up feature filling.

Determination of Total Protein Concentration in Solution Using Gold Electrode Modified with Silver Nanoparticles

AbstractGold electrodes were modified with silver nanoparticles and Ag/AgCl redox conversion was recorded by cyclic voltammetry in protein containing electrolyte solution. The charge of the reduction peak decreased with the increase of the total protein concentration. This correlation was better for solutions containing bovine serum albumin as a standard than for the samples of human saliva. The results of these electroanalytical measurements show that the method can be used to determine protein concentration in electrolyte solution in the range from 0.01 to 0.2 mg mL−1, though reproducibility of analysis of real samples must be further improved.

Compressed multiwall carbon nanotube composite electrodes provide enhanced electroanalytical performance for determination of serotonin

Serotonin (5-HT) is an important neurochemical that is present in high concentrations within the intestinal tract. Carbon fibre and boron-doped diamond based electrodes have been widely used to date for monitoring 5-HT, however these electrodes are prone to fouling and are difficult to fabricate in certain sizes and geometries. Carbon nanotubes have shown potential as a suitable material for electroanalytical monitoring of 5-HT but can be difficult to manipulate into a suitable form. The fabrication of composite electrodes is an approach that can shape conductive materials into practical electrode geometries suitable for biological environments. This work investigated how compression of multiwall carbon nanotubes (MWCNTs) epoxy composite electrodes can influence their electroanalytical performance. Highly compressed composite electrodes displayed significant improvements in their electrochemical properties along with decreased internal and charge transfer resistance, reproducible behaviour and improved batch to batch variability when compared to non-compressed composite electrodes. Compression of MWCNT epoxy composite electrodes resulted in an increased current response for potassium ferricyanide, ruthenium hexaammine and dopamine, by preferentially removing the epoxy during compression and increasing the electrochemical active surface of the final electrode. For the detection of serotonin, compressed electrodes have a lower limit of detection and improved sensitivity compared to non-compressed electrodes. Fouling studies were carried out in 10μM serotonin where the MWCNT compressed electrodes were shown to be less prone to fouling than non-compressed electrodes. This work indicates that the compression of MWCNT carbon-epoxy can result in a highly conductive material that can be moulded to various geometries, thus providing scope for electroanalytical measurements and the production of a wide range of analytical devices for a variety of systems.

Theory of square wave voltammetry of amalgam forming ions at spherical electrodes

A theoretical model of reversible reduction of amalgam forming ion on stationary mercury drop electrode is developed for square wave voltammetry. The dependence of dimensionless net peak current on the dimensionless inverse electrode radius is investigated. This relationship is not linear, but it is a curve with two asymptotes. These results apply to electroanalytical measurements at spherical microelectrodes.

Comparative electrochemical response of estrone at glassy-carbon, nitrogen-containing tetrahedral amorphous carbon and boron-doped diamond thin-film electrodes

The anodic oxidation of estrone was comparatively investigated at glassy carbon (GC), nitrogen-incorporated tetrahedral amorphous carbon (ta-C:N) and boron-doped diamond (BDD) electrodes. The ta-C:N and BDD electrodes are characterized by a wider working potential window and lower background current that for GC. The latter is because of a reduced level of pseudocapacitance on the former electrodes due to the absence of significant levels of redox-active surface carbon–oxygen functionalities. The irreversible oxidation of estrone was recorded at a similar potential for all three electrodes (0.9–0.95V) in 0.5molL−1 H2SO4. The voltammetric peak current decreased some for all the electrodes with potential cycling suggestive of some response attenuation by reaction product adsorption (or slow desorption). From the dependence of the oxidation peak potential and current with solution pH, it was possible to conclude that the electrooxidation of estrone involves the transfer of two electrons accompanied by the loss of two protons at pH<10. Voltammetric and chronocoulometric data indicated the oxidation reaction kinetics on all three electrodes were under mixed control by both diffusion and adsorption. This was most apparent for GC where estrone adsorption was greatest (145pmolcm−2). The greater adsorption on GC can be explained by electronic and or chemical effects associated with the graphitic edge plane sites. In contrast, the estrone adsorption on ta-C:N and BDD was significantly lower, about 1/10 of that on GC. This behavior is due to the differences in the types and density of functional groups and the absence of an extended π-electron system in both materials. In summary, the here-reported properties of the ta-C:N and BDD electrodes suggest that both could be excellent candidates for electroanalytical measurements involving the detection and/or determination of estrone and similar hormones.

Impact of Electrostatics on the Chemodynamics of Highly Charged Metal–Polymer Nanoparticle Complexes

In this work, the impact of electrostatics on the stability constant, the rate of association/dissociation, and the lability of complexes formed between Cd(II), Pb(II), and carboxyl-modified polymer nanoparticles (also known as latex particles) of radius ∼ 50 nm is systematically investigated via electroanalytical measurements over a wide range of pHs and NaNO3 electrolyte concentrations. The corresponding interfacial structure and key electrostatic properties of the particles are independently derived from their electrokinetic response, successfully interpreted using soft particle electrohydrodynamic formalism, and complemented by Förster resonance energy transfer (FRET) analysis. The results underpin the presence of an ∼0.7-1 nm thick permeable and highly charged shell layer at the surface of the polymer nanoparticles. Their electrophoretic mobility further exhibits a minimum versus NaNO3 concentration due to strong polarization of the electric double layer. Integrating these structural and electrostatic particle features with recent theory on chemodynamics of particulate metal complexes yields a remarkable recovery of the measured increase in complex stability with increasing pH and/or decreasing solution salinity. In the case of the strongly binding Pb(II), the discrepancy at pH > 5.5 is unambiguously assigned to the formation of multidendate complexes with carboxylate groups located in the particle shell. With increasing pH and/or decreasing electrolyte concentration, the theory further predicts a kinetically controlled formation of metal complexes and a dramatic loss of their lability (especially for lead) on the time-scale of diffusion toward a macroscopic reactive electrode surface. These theoretical findings are again shown to be in agreement with experimental evidence.