Nernstian Behavior Research Articles

Quantifying the Temperature Dependence of the Multi-Species, Multi-Reaction Model

The Multi-Species, Multi-Reaction (MSMR) model utilizes slow-rate lithiation and delithiation data to estimate parameters such as total fraction of available host sites, reference potential, and deviation from Nernstian behavior.1 The MSMR model has successfully been applied to a variety of common lithium-ion materials such as lithated silicon2, graphite, iron phosphate and spinel manganese oxide.3-5 In this presentation, the temperature impact on MSMR gallery parameters will be presented for coal-derived and commercially available graphite. The temperature dependent trends observed and their impact on a system will be discussed. A comparison of the MSMR parameters for each material will be provided. The commonalities and differences in the trends will be discussed and linked back to the differences observed in the graphite material properties.

Quantifying the Temperature Dependence of the Multi-Species, Multi-Reaction Model: Part II. Estimation of Entropy Coefficient for Meso-Carbon Micro-Bead Graphite

In Part 1 of this paper, the temperature impact on the Multi-Species, Multi Reaction (MSMR) model was studied. This was accomplished by acquiring data from slow rate lithiation and delithiation of a meso-carbon micro-bead (MCMB) graphite. Through this analysis, the temperature impact on the total fraction of available host sites in a particular MSMR gallery (Xj), the impact on the reference potential ( Ujo ), and the impact on the parameter detailing the deviation from Nernstian behavior (ω j) was determined. Here, the intercalation material is discussed, compared to traditional methods of acquiring the entropy coefficient, and comparison is made to previous mathematical estimates. Some of the challenges in using temperature dependent constant rate charge and discharge data as compared to the potentiodynamic entropy coefficient calculation method are also discussed, and a recommendation for future applications is proposed.

Quantifying the Temperature Dependence of the Multi-Species, Multi-Reaction Model. Part 1: Parameterization for a Meso-Carbon Micro-Bead Graphite

In this work, the temperature impact on the Multi-Species, Multi-Reaction (MSMR) model is studied. This is accomplished by acquiring data from slow rate lithiation and delithiation of a meso-carbon micro-bead (MCMB) graphite. The MSMR model is used to simulate linear-sweep voltammetry data of a porous electrode composed of graphite, and because the electrode is close to a state of dynamic equilibrium, the peaks in the differential voltage spectroscopy plot can be analyzed. Through this analysis, the temperature impact on the total fraction of available host sites in a particular MSMR gallery (Xj), the impact on the reference potential (U°j), and the impact on the parameter detailing the deviation from Nernstian behavior (ω j) can be found. This is the first time the temperature dependence of the MSMR parameters have been experimentally analyzed. In Part 2, the impact of the temperature dependence of the MSMR parameters on the entropy coefficient of an intercalation material will be studied.

All-solid-state K+ sensing array based on Au@polystyrene nanocomposites.

All-solid-state ion selective electrodes (ASS-ISEs) areeasy to miniaturize and array, meeting the needs of home sensing devices. However, ASS-ISEs still faces challenges in accuracy and stability due to basic potential changes caused by non-specific adsorption of charged background compositions and the complex electrode preparation steps. To this end, our group successfully subtracted the background signal by integrating a self-calibrating channel in the sensing array and simplified the electrode preparation steps by preparing multi-functional PS-Au nanocomposites. However, the uniformity and gold content of PS-Au nanocomposites are difficult to control, so Au@PS nanocomposites are prepared as sensor materials in this paper to further reduce the differences between batches of electrodes. K+ Au@PS sensing array can be obtained by directly dropping Au@PS nanocomposites on the screen-printed carbon electrodes (SPCEs), which shows a near Nernstian behavior in the range 1.0 × 10-3M to 0.3M and good reproducibility in real sample testing. The detection results by K+ Au@PS sensing array for K+ in human morning urine agreed well with that tested by ICP-AES, which make the K+-ASS-ISE suitable for home health monitoring.

Potentiometric determination of the local anesthetic procaine in pharmaceutical samples

In this study, a new potentiometric sensor was developed for the determination of the local anesthetic drug procaine in pharmaceutical samples. Procaine (Pr)–Tetraphenlyborate (TPB) ion–pair was synthesized and used as a sensor material. Potentiometric sensors using the synthesized ion pair (Pr–TPB), poly(vinyl chloride) (PVC) and o–nitrophenyloctyl ether (o–NPOE) in different proportions were prepared and their performance properties were tested. Among the prepared sensors, the best potentiometric response characteristics were obtained with the sensor composition Pr–TPB:PVC:o–NPOE in the ratio of 6.0:32.0:62.0 (w/w %). The new procaine sensor developed in the present study had a near–Nernstian behavior of 54.1 ± 3.3 mV/per decade and a low detection limit of 3.18 × 10−5 mol L−1 in the concentration range of 1.0 × 10−1–1.0 × 10−4 mol L−1. Additionally, the sensor had a response time of less than 10 s and could work in a wide pH range for two different concentration values without being affected by pH changes. Finally, the new procaine potentiometric sensor was used to detect procaine in injection samples and successfully determined procaine concentrations with high recoveries.

Electrochemical Determination of Catechol Using a Disposable Printed Electrode with Conductive Ink Based on Graphite and Carbon Black

Catechol (CT) is a phenolic compound widely used in various industrial sectors, but it is toxic; thus, there is a need for methods that aim to identify and quantify the existence of residues of this material in the environment. In this study a disposable printed electrochemical sensor was developed as an effective alternative for determining CT in water samples. The electrode, called SPEC, was manufactured using the screen-printing method using polyethylene terephthalate (PET) as a support, in which a conductive ink based on carbonaceous materials was used to print the working and auxiliary electrodes and a silver/silver chloride of ink on the reference electrode. The optimal ratio for the conductive ink was 6.25% carbon black, 35.42% graphite, and 58.33% nail polish. The ink obtained was characterized by scanning electron microscopy (SEM). The assessment of the effect of pH on the redox process showed Nernstian behavior (0.057 V pH−1), indicating that the process involves the same number of protons and electrons. Under optimized conditions, with 0.2 mol L−1 acetate buffer at pH 5.0, and by square wave voltammetry, the sensor presented sensitivity values of 0.31 μA L μmol−1, a detection limit of 5.96 μmol L−1, and a quantification limit of 19.87 μmol L−1. The sensor was applied to determine CT in tap water samples, and the results showed recoveries between 97.95 and 100.17%.

Square-wave voltammetric evaluation of electrochemical constants: Comparative study with other techniques

Square-wave voltammetry was employed for evaluation of electrochemical rate constants for soluble hexacyanoferrate ions as well as for iron hexacyanoferrate (Prussian blue) and nickel hexacyanoferrate immobilized on carbon electrodes. Modelling of square-wave response of immobilized species with assumption of Nernstian behavior, the dimensionless net current peak splitting occurs. The peak value decreases with the rise of square-wave amplitude Esw and splits around the common value of 50 mV. For a quasireversible behavior, the dimensionless net peak current has an extremum depending on both frequency and Esw. At 40 mV, the frequency in the extremum almost coincides with the surface electrochemical rate constant ksur. For practical confirmation, the Prussian blue film was studied at different frequencies (Esw = 50 mV). At lower values, the reaction is relatively fast and net peak current splitting occurs. At higher values, the net response reaches its maximum allowing to evaluate the surface electrochemical rate constant. A comparative investigations of electrode kinetics (for both surface and heterogeneous electrochemical constant) by different electrochemical methods proved the advantages of square-wave pulse technique. In contrast to cyclic voltammetry and electrochemical impedance spectroscopy, the square-wave voltammetry has lower variation of estimated parameters, relatively simple calculations, uncomplicated simulation of different mechanisms.

Non-ideal nernstian behavior in organic electrochemical transistors: fundamental processes and theory.

Despite the successful implementation of organic electrochemical based devices (OEDs), fundamental processes that regulate their operations and sensing capabilities, specifically those related to ion-to-electron transduction, remain unclear. Indeed, there is still a lack of fundamental models to explain the steady-state and transient characteristics of OEDs, associating fundamentals of the physical-chemistry of the pair polymer-electrolyte with the output performance of such devices. In this study, we bring new highlights to a thermodynamic-based model that qualitatively and quantitatively describes OEDs operation, with a special focus on the organic electrochemical transistor (OECT). In this context, we introduce novel interpretations for traditional drain current models, grounded in thermodynamic and electrochemical principles. The model fitting parameters are correlated to the physical and chemical properties of the polymer-electrolyte pair, and it has been shown to explain trends observed in experimental results from the literature. Moreover, our model reveals that a non-Nerstian electrochemical behavior dominates OECT operation. Also, by analyzing experimental data, we are able to generate guidelines for material design and device development, targeting highly sensitive electrochemical biosensors and devices.

Comparison of selectivity and sensitivity of various ferric selective electrodes prepared using N-((bis(dimethyl amino)methylene)carbamothioyl)benzamide.

N-((Bis(dimethyl amino)methylene)carbamothioyl)benzamide (NBMCB) was synthesized, characterized, and used as an ionophore for producing three novel ion-selective potentiometric sensors for Fe(III) determination. Firstly, using the molecular mechanic-based MMFF94 method, the most stable NBMCB's conformer and its isosteric complexes with various cations were determined. According to the Gibbs free energy results of the reaction, the thermodynamic complexation reactivity of Fe(III) and the ligand was acceptable. These results were obtained using the B3LYP approach and the 6-31G(d,p) basis set that was substituted for heavy metals by the LanL2DZ basis set. We used UV-visible spectrophotometry to confirm the tendency of NBMCB to react with Fe(III). Generally, three diverse liquid membrane ferric selective electrodes were obtained by the use of the specified ligand: classic with a liquid internal electrolyte-ferric selective electrode (LIE-FSE), solid state-FSE (SS-FSE), and coated wire-FSE (CW-FSE). The reactions exhibited Nernstian behavior across all electrodes. The limit of detection was enhanced for the SS-FSE (3 × 10-9 M) and the CW-FSE (3 × 10-7 M) in comparison with that of the LIE-FSE (7 × 10-7 M). The lifetime of the LIE-FSE was 8 weeks, while it was 10 weeks for the SS-FSE and the CW-FSE. Elimination of the internal solution reduced the limit of detection and prolonged the lifespan of the sensors. Also, the three electrodes all had a short response time of around 5-7 s. The sensors were utilized as indicator electrodes during the potentiometric titration of Fe(III) using ethylenediaminetetraacetic acid.

Fabrication of ZnO/ZnAl2O4/Au Nanoarrays through DC Electrodeposition Utilizing Nanoporous Anodic Alumina Membranes for Environmental Application.

In this study, anodic aluminum oxide membranes (AAOMs) and Au-coated AAOMs (AAOM/Au) with pore diameters of 55 nm and inter-pore spacing of 100 nm are used to develop ZnO/AAOM and ZnO/ZnAl2O4/Au nanoarrays of different morphologies. The effects of the electrodeposition current, time, barrier layer, and Au coating on the morphology of the resultant nanostructures were investigated using field emission scanning electron microscopy. Energy dispersive X-ray and X-ray diffraction were used to analyze the structural parameters and elemental composition of the ZnO/ZnAl2O4/Au nanoarray, and the Kirkendall effect was confirmed. The developed ZnO/ZnAl2O4/Au electrode was applied to remove organic dyes from aqueous solutions, including methylene blue (MB) and methyl orange (MO). Using a 3 cm2 ZnO/ZnAl2O4/Au sample, the 100% dye removal for 20 ppm MB and MO dyes at pH 7 and 25 °C was achieved after approximately 50 and 180 min, respectively. According to the kinetics analysis, the pseudo-second-order model controls the dye adsorption onto the sample surface. AAOM/Au and ZnO/ZnAl2O4/Au nanoarrays are also used as pH sensor electrodes. The sensing capability of AAOM/Au showed Nernstian behavior with a sensitivity of 65.1 mV/pH (R2 = 0.99) in a wide pH range of 2-9 and a detection limit of pH 12.6, whereas the ZnO/ZnAl2O4/Au electrode showed a slope of 40.1 ± 1.6 mV/pH (R2 = 0.996) in a pH range of 2-6. The electrode's behavior was more consistent with non-Nernstian behavior over the whole pH range under investigation. The sensitivity equation was given by V(mV) = 482.6 + 372.6 e-0.2095 pH at 25 °C with R2 = 1.0, which could be explained in terms of changes in the surface charge during protonation and deprotonation.

Measuring Electrochemical Potentials for Health Monitoring of Redox Flow Batteries

Long-duration energy-storage (LDES) systems have the potential to transform the electric grid. Redox Flow Batteries (RFBs) have many unique attributes that make this battery architecture ideally suited for grid-scale LDES, namely: independent power and energy; long cycle life, even with deep cycles; inherently superior safety [1]; and easy recyclability. However, despite a recent renaissance in RFB technologies, assessing the durability of RFB cells is a topic that has not received much attention in the open literature, and further research is needed to better understand the performance and degradation mechanisms [2]. In-situ health monitoring of RFBs is critical for maximizing their lifetime and efficiency. Measurements of the electrochemical potentials of the electrodes and the electrolyte can provide insights into whether operating parameters are being adhered to and can potentially detect failure mechanisms occurring real-time within the battery. Since the electrochemical potential of both the positive and negative electrolytes exhibits Nernstian behavior, they are convertible to state-of-charge (SOC) measurements. Ensuring that the electrolyte stays within a desired SOC window during operation is essential for the mitigation of undesirable side reactions, such as the hydrogen-evolution reaction (HER) [3]. In addition, measurements of the potential difference between the electrode and the electrolyte, commonly known as overpotential, during charging and discharging processes allow for independent quantification of the reaction efficiency at each electrode. Factors affecting this reaction efficiency may include reaction kinetics, the mass transport of active species to the electrodes, the plating of impurities onto the electrode surface, and the mobility of ions across the ion-exchange membrane. Analysis of overpotential can also be useful in detecting failure mechanisms relating to these various factors [4]. Largo Clean Energy has developed multiple methods to measure electrochemical potentials in all-vanadium RFBs (VRFBs). The focus of this talk will be on how one can use these different measurements to assess the performance of VRFB cells. References R. Wittman, M. L. Perry, T. N. Lambert, B. R. Chalamala, and Y. Preger, “Perspective – On the Need for Reliability and Safety of Grid-Scale Aqueous Batteries,” J. Electrochemical Society, 167 (2020).Y. Yao, J. Lei; Y. Shi; F. Ai; T. C. Lu, “Assessment methods and performance metrics for redox flow batteries,” Nature Energy, 6 (2021).C. Tai-Chieh Wan, K. E. Rodby, M. L. Perry, Y.-M. Chiang, F. R. Brushett, “Hydrogen evolution mitigation in iron-chromium redox flow batteries via electrochemical purification of the electrolyte,” J. of Power Sources, 554 (2023).M. L. Perry and R. M. Darling, “Development of a Simple and Rapid Diagnostic for Redox Flow-Battery Cells,” Symposium I02: Frontiers of Chemical/Molecular Engineering in Electrochemical Energy Technologies, 242nd ECS Meeting, (2022).

An Ion Selective Electrode Study: Naproxen (NA) Quantification in Pharmaceutical Formulations

AbstractThis study presents fabrication, characterizations and application of an ion‐selective electrode based on naproxen‐sodium tungstate (NA‐ST) ion pairs as a sensor for the quantification of naproxen in a number of pharmaceutical formulations. The ISE is made of the sensor (electrochemical active species or ion pairs) as well as polyvinyl chloride (PVC) and dibutyl phthalate as supporting and plasticizer materials, respectively. The characterizations of the sensor film comprise usage of Fourier transform infrared (FTIR), scanning electron microscope (SEM); in addition to determining the stoichiometric ratio between the components of the sensor using elemental analysis (CHN microanalysis). The analytical evaluation of the sensor film based on selectivity, sensitivity, and Nernstian behavior (55.8±1.1 mV/decade) are shown. The relative high selectivity of sensor towards NA as a target in the presence of several common interferents are exhibited. The ISE possesses a satisfactory sensitivity by recording a detection limit of 0.005 μM. The sensor also experiences a Nernstian behavior during all measurements. The dynamic linear range lies between 0.01 and 100 μM at 25 °C with R2=0.9998. The shelf life is 17 s and longevity lasts four months.

Experimental manifestation of redox-conductivity in metal-organic frameworks and its implication for semiconductor/insulator switching

Electric conductivity in metal-organic frameworks (MOFs) follows either a band-like or a redox-hopping charge transport mechanism. While conductivity by the band-like mechanism is theoretically and experimentally well established, the field has struggled to experimentally demonstrate redox conductivity that is promoted by the electron hopping mechanism. Such redox conductivity is predicted to maximize at the mid-point potential of the redox-active units in the MOF, and decline rapidly when deviating from this situation. Herein, we present direct experimental evidence for redox conductivity in fluorine-doped tin oxide surface-grown thin films of Zn(pyrazol-NDI) (pyrazol-NDI = 1,4-bis[(3,5-dimethyl)-pyrazol-4-yl]naphthalenediimide). Following Nernstian behavior, the proportion of reduced and oxidized NDI linkers can be adjusted by the applied potential. Through a series of conductivity measurements, it is demonstrated that the MOF exhibits minimal electric resistance at the mid-point potentials of the NDI linker, and conductivity is enhanced by more than 10000-fold compared to that of either the neutral or completely reduced films. The generality of redox conductivity is demonstrated in MOFs with different linkers and secondary building units, and its implication for applications that require switching between insulating and semiconducting regimes is discussed.

An Ion Selective Electrode Construction Based on Phosphomolybdic Acid for Atropine Sulfate Detection

AbstractThis study presents an attempt has been carried out to fabricate ion‐selective electrodes (ISEs) for the determination of Atropine sulfate (AT) in pharmaceutical formulas. Three plasticizers; namely, di‐n‐butyl phthalate (DBP), bis (2‐ethyl hexyl) phthalate (BEP), nitrobenzene (NB), and tetrahydrofuran (THF) were used in the fabrication of the three ion selective electrodes after incorporating into polyvinyl chloride (PVC) and symbolized as E1, E2, and E3, respectively. Beyond evaluation of the three ISEs, it has been confirmed that one with DBP experienced the most Nernstian behaviour. For the electrode of interest, the slope and detection limit are 55.02 mV/decade and 1.1×10−6 M, respectively. The linear range was 1.0×10−2–1.0×10−5 M (R2=0.9999) with recording 5 s and 45 days; sequentially, for the response time and shelf life of E1 electrode. The sensor has experienced high selectivity for atropine sulfate, verifying from the selectivity coefficient data for a number of potential interferences. The statistical analysis using t‐test and F‐test indicates the eligibility of constructed electrode for utilization in field of pharmaceutical analysis. A satisfactory accordance has been obtained between the proposed electrode for atropine sulfate and the standard method. This methodology is supposed to be applicable in quality control and even clinical diagnosis.

Green fluorescent protein-multi walled carbon nanotube based polymeric membrane electrode for bismuth ion detection

Developing a sensor that is selective only to the target metal type remains a major challenge. Polymeric membrane electrodes are versatile devices with exceptional analytical simplicity and are frequently used in environmental analysis. A novel polymeric membrane electrode (PME) was proposed for the determination of bismuth ions with high sensitivity. In an unconventional approach, Green Fluorescent Protein (GFP) was used as an ionophore in the fabrication of PME electrodes. GFP, a member of the fluorescent protein family, has emerged as biocompatible tools, especially for biomedical applications, bioimaging, intracellular monitoring, sensors, and optical devices, and has attracted great attention thanks to its unique advantages. In this study, a high performance compatible PME has been developed by solvent casting method integrating GFP doped elastomeric multi-walled carbon nanotubes (MCNTs) into conductive plasticized polyvinyl chloride (PVC). The high metal-binding affinity of GFP made these proteins potential ionophores in the PME structure. The morphological structures of the produced GFP-doped MWCNT were characterized by HRTEM. Potentiometric behaviors and performance of the produced bismuth selective PME are summarized for both analytical and real examples. The prepared electrode exhibited Nernstian behavior with a slope of 19 ± 1 mV and a low detection limit of 4.3 × 10−6 M, and the electrode response time was observed as <40–45 s.

The use of bis–thiadiazole and bis–oxadiazol derivatives as ionophores: A novel copper(II)–selective potentiometric electrodes

In this study, bis–thiadiazole and bis–oxadiazol derivative molecules were synthesized and their ionophore properties were investigated. The synthesized bis–thiadiazole and bis–oxadiazol derivative molecules exhibited selectivity towards copper(II) ions. Electrodes prepared with 5,5′-(1,4-phenylene)bis(1,3,4-thiadiazol-2-amine) (4) exhibited more ideal potentiometric behavior than electrodes prepared with 5,5′-(1,4-phenylene)bis(1,3,4-oxadiazol-2-amine) (7). The copper(II)–selective electrode prepared with bis–thiadiazole derivative molecule (4) have near–Nernstian behavior (32.3 ± 3.3 mV/decade) over a wide linear working range of 1.0 × 10−6– 1.0 × 10−1 mol L−1 (R2 = 09967). The electrode exhibited a low detection limit of 9.02 × 10−7 mol L−1. These novel copper(II)–selective potentiometric electrodes were not only economical because the electroactive material was produced in the laboratory, but also had a fast response time, good selectivity and repeatability. The potential response of the electrode remained unaffected of pH in the range of 4.0 – 9.0. Finally, the developed electrode performed the determination of copper(II) ions in various water samples with very high recoveries.

Fabrication and characterization of mullite nano-ceramic materials for use in carbon paste ion selective electrode to estimate carcinogenic Cd (II) ion in real and human samples

Ion-selective electrodes are preferable to competing electrochemical methods for potentiometric detections regarding operating convenience, speed, and cost. The development of a novel class of carbon-paste electrochemical sensor that exploits synthetic mullite (3Al2O3.2SiO2) nanoparticles as an ionophore is investigated in this research. These mullite nanoparticles were synthesized using the sol–gel process, and a variety of methods were utilized to characterize them, including X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) coupled with EDAX, and Brunauer-Emmett-Teller (BET) analysis. Nano-mullite's crystal structure has been verified by the XRD technique and crystallite size was established by the Debye-Scherrer equation (average crystallite size 9 nm). SEM and TEM have verified its nanoscale (the particle size between 16.08 nm and 45.5 nm). The BET study confirms the huge surface area (82.1164 m2/g), average pore size equal to 5.323 nm, and mesoporous structure of the mullite nanoparticle. Mullite nanoparticles, which have a substantial surface area, a porous structure, nano size, and electrical activity, are incorporated into the electrode composition to speed up the processes of electron transfer. The modified carbon paste electrode (MCPE) has been estimated in the function of a selective sensor for cadmium ion detection. Under ideal conditions, the potentiometric approach verified a straight reactivity forward into Cd (II) ion in varying concentrations from 1.0 × 10-8 to 1.0 × 10-2 mol/L with a limit of detection of 1.0 × 10-8 mol/L and a Nernstian slope of 29.49 ± 0.24 mV decade-1. The paste composition that produced the best results had, in order, 67.3 % graphite, 3.5 % TCP, and 2.7 % nano-mullite. The designed sensor has a short response time of 6 s, may well be maintained for nearly 10 weeks in the pH interval of 3.0 to 8.0, and had good thermal stability in the interval of 10 to 60 °C without deviating from Nernstian behavior. Considering the diversity of metal ions, the electrode showed good Cd(II) ion selectivity. Cd(II) ion was measured in water, cigarettes, hair, nails, natural and synthetic dyes. The outcomes of validation techniques perform superior to the ICP methodology. The potentiometric titration of Cd(II) ions with EDTA was successfully realized utilizing the MCPE with a sharp inflexion at the endpoint.

Modified carbon paste ion selective electrode for determining Cr(iii) ions in aqueous solutions and some real samples using tetragonal zirconia nanoparticles.

Tetragonal zirconia (t-ZrO2) nanoparticles (ionophore) are used in newly designed and improved ion selective electrodes for chromium ion detection as an alternative, low-cost, high-precision, and selectivity method. Tetragonal zirconia nanoparticles were synthesized using a modified co-precipitation technique and calcined at 1000 °C for an hour. The phase composition, surface area, microstructure, pore size and particle size of synthesized t-ZrO2 nanoparticles were examined using the X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), transmission electron microscope (TEM) and scanning electron microscopy (SEM) attached with an EDAX unit, respectively. Results from XRD showed that the t-zirconia was synthesized and have nanocrystallites size about 20.2 nm. The nano size of t-ZrO2 was confirmed by the SEM and TEM (the particle size between 26.48 and 40.4 nm), the mesoporous character (average pore size about 4.868 nm) and large surface area (76.2802 m2 g-1) was confirmed by BET analysis. The paste composition with 67.3 : 30.5 : 2.7 (wt%) graphite, t-ZrO2, and TCP, respectively, exhibited the best results. With a detection limit of 1.0 × 10-8 mol L-1, the electrode displayed a good Nernstian slope of 19.50 ± 0.10 mV decade-1 over the concentration range from 1.0 × 10-2 to 1.0 × 10-8 mol L-1 of Cr(iii) ions. The built-in sensor displayed a quick response time (7 s), was highly thermally stable in the range of 10 to 60 °C without departing from Nernstian behaviour and could be used for about 60 days in the pH range of 2.0 to 6.0. The electrode demonstrated excellent selectivity for the Cr(iii) ion towards a variety of metal ions. For chromium ion determination, numerous spiked real samples, including honey, water, tea, coffee, milk, cheese, and cosmetics, were used. Validation methods were used, and the results showed that there is no significant difference between the two methods (ICP and ISE) at a 95% confidence level. In several real water samples, the estimated limits of detection, limits of quantification, percent recovery, standard deviation, and relative standard deviation showed the effectiveness of the proposed electrode in the potentiometric detection of Cr(iii) ions.

Ion-selective electrodes based on laser-induced graphene as an alternative method for nitrite monitoring.

Nitrite is an important food additive for cured meats; however, high nitrite levels pose adverse health effects to humans. Hence, monitoring nitrite concentration is critical to comply with limits imposed by regulatory agencies. Laser-induced graphene (LIG) has proven to be a scalable manufacturing alternative to produce high-performance electrochemical transducers for sensors. Herein, we expand upon initial LIG studies by fabricating hydrophilic and hydrophobic LIG that are subsequently converted into ion-selective sensors to monitor nitrite in food samples with comparable performance to the standard photometricmethod (Griess method). The hydrophobic LIG resulted in an ion-selective electrode with improved potential stability due partly to a decrease in the water layer between the electrode and the nitrite poly(vinyl) chloride-based ion-selective membrane. These resultant nitrite ion-selective sensors displayed Nernstian response behavior with a sensitivity of 59.5mV dec-1, a detection limit of 0.3 ± 0.1mg L-1(mean ± standard deviation), and a broad linear sensing range from 10-5 to 10-1M, which was significantly larger than currently published nitrite methods. Nitrite levels were determined directly in food extract samples of sausage, ham, and bacon for 5min. These sensor metrics are significant as regulatory agencies limit nitrite levels up to 200mg L-1in finished products to reduce the potential formation of nitrosamine (carcinogenic compound). These results demonstrate the versatility of LIG as a platform for ion-selective-LIG sensors and simple, efficient, and scalable electrochemical sensing in general while demonstrating a promising alternative to monitor nitrite levels in food products ensuring regulatory compliance.

Redox Potentials of Magnetite Suspensions under Reducing Conditions.

Predicting the redox behavior of magnetite in reducing soils and sediments is challenging because there is neither agreement among measured potentials nor consensus on which Fe(III) | Fe(II) equilibria are most relevant. Here, we measured open-circuit potentials of stoichiometric magnetite equilibrated over a range of solution conditions. Notably, electron transfer mediators were not necessary to reach equilibrium. For conditions where ferrous hydroxide precipitation was limited, Nernstian behavior was observed with an EH vs pH slope of -179 ± 4 mV and an EH vs Fe(II)aq slope of -54 ± 4 mV. Our estimated EHo of 857 ± 8 mV closely matches a maghemite|aqueous Fe(II) EHo of 855 mV, suggesting that it plays a dominant role in poising the solution potential and that it's theoretical Nernst equation of EH[mV] = 855 - 177 pH - 59 log [Fe2+] may be useful in predicting magnetite redox behavior under these conditions. At higher pH values and without added Fe(II), a distinct shift in potentials was observed, indicating that the dominant Fe(III)|Fe(II) couple(s) poising the potential changed. Our findings, coupled with previous Mössbauer spectroscopy and kinetic data, provide compelling evidence that the maghemite/Fe(II)aq couple accurately predicts the redox behavior of stoichiometric magnetite suspensions in the presence of aqueous Fe(II) between pH values of 6.5 and 8.5.