Peak Separation Research Articles

Key role of adsorption site abundance in the direct electrochemical co-detection of estradiol and dopamine

Estradiol (E2) is a hormone that influences various aspects of women’s health. Beyond its reproductive functions, E2 impacts neurotransmitter systems such as dopamine (DA). Vertically aligned carbon nanofibers (VACNFs) have shown good sensitivity, selectivity against ascorbic acid (AA) and uric acid (UA), biocompatibility, and reduced fouling in DA sensing. In this study, we explore the use of Ti-Ni-CNF electrodes with CNFs grown for 5 min and 30 min for the direct electrochemical co-detection of E2 and DA. The longer growth time led to a 142% increase in average CNF length and a 36% larger electroactive surface area. In E2 detection, the electrodes demonstrate a wide linear range of 0.05–10 µM and sensitivity of 0.016 and 0.020 µA/µM for Ti-Ni-CNF-5 min and Ti-Ni-CNF-30 min, respectively. The sensor performance remains largely unaffected even in the presence of other steroid hormones such as progesterone and testosterone. Co-detection of equimolar E2 and DA shows promising peak separation of 0.34 ± 0.01 V and repeatability after 10 measurements. A notable improvement in the E2/DA peak current ratio, from 0.53 ± 0.07 to 0.81 ± 0.16, was achieved with the increased CNF length. Our results demonstrate the influence of adsorption sites in electrochemical detection, especially for analytes such as E2 and DA that both rely on adsorption for oxidation. While detecting small and fluctuating physiological concentrations remains a challenge, these findings can be used in choosing and fabricating electrode materials for more accurate and accessible continuous hormone measurements, including the possibility of multianalyte sensing platforms.Graphic abstract

A terahertz broadband and narrowband switchable absorber based on joint modulation of vanadium dioxide and graphene surfaces

Abstract In this paper, a terahertz broadband and narrowband switchable absorber is proposed. The absorption performance tuning for both broadband and narrowband functions is realized based on the joint modulation of vanadium dioxide (VO2) and graphene surfaces. Concretely, while VO2 is in the metallic state, the absorber achieves broadband absorption function. The overall bandwidth of over 90% absorption is 4.04 THz corresponding to a relative bandwidth of 84%. Through regulating the conductivity of VO2, dynamic tuning of the absorption amplitude is obtained and the modulation depth is 96%. By manipulating the graphene Femi energy and VO2 conductivity simultaneously, dynamic tuning of the absorption bandwidth is realized. In particular, the spectral center frequency of broadband absorption remains stable without drifting during the tuning process. While VO2 is in the insulating state, the absorber achieves narrowband absorption function. Calculated results show that two separate perfect absorption peaks are formed, and the absorption amplitudes are 99.6% and 99.2% respectively. Through regulating the Fermi energy of graphene surface, the dynamic tuning of narrowband absorption frequency is realized. Compared with the ones reported in recent years, our absorber has the advantage on function realization, absorption characteristics and performance tuning.

Development and Application of HPLC and UFLC Methods for the Analysis of Cardiovascular Drugs

Separation and identification of amiloride, metoprolol, hydrochlorothiazide, Carvedilol and amlodipine, in human plasma using the presented SPE and HPLC procedures was selective, efficient, robust, economical, environmentally friendly, and repeatable. Because plasma samples showed no evidence of a secondary peak, it was determined that the claimed drug-drug interaction between cardiovascular medications did not occur. Furthermore, no new peak was generated, indicating no metabolic product. This is the first report on isolating and identifying these nine cardiovascular medicines. Thus, SPE and HPLC techniques may be used to investigate these 5 cardiovascular medications. Successful monitoring of these medications in human plasma was achieved using the established SPE and HPLC technologies. The results of this inquiry were contrasted with those that had already been released. In comparison to other works in the literature, it was determined that the current study had the best complete baseline separation and lowest detection limit. The retention, separation, and resolution factors were discovered to have ranges of 0.07-9.14, 1.44-4.21, and 2.15-18.66, respectively. The SPE and UFLC techniques created and verified for this purpose were used to examine human plasma samples for the presence of cardiovascular drugs. Peak retention, separation, resolution, and symmetry all matched the reference samples' values. The results for symmetry, separation, and resolution were all in agreement with the reference samples. The methods used to separate and identify amiloride, metoprolol, hydrochlorothiazide; Carvedilol and Amlodipine in human plasma were found to be selective, effective, hardy, affordable, environmentally friendly, and reproducible, according to the authors. The selectivity of the SPE technique was validated by the absence of any secondary signal in the plasma samples. Additionally, there was no evidence of these drugs degrading in the plasma sample. This is the initial report on the simultaneous isolation and identification of these eight medications. The well-known SPE and UFLC techniques were successfully used to monitor these drugs in human plasma. Therefore, these drugs can be detected in any plasma sample using SPE or UFLC methods

Development and Application of HPLC and UFLC Methods for the Analysis of Anti Histaminic Drugs

Research focused on medications used to treat allergic reactions. The results of this inquiry were contrasted with those that had already been released. In comparison to other works in the literature, it was determined that the current study had the best complete baseline separation and lowest detection limit. The retention, separation, and resolution factors were discovered to have ranges of 0.07-9.14, 1.44-4.21, and 2.15-18.66, respectively. The SPE and UFLC techniques created and verified for this purpose were used to examine human plasma samples for the presence of antihistaminic drugs. Peak retention, separation, resolution, and symmetry all matched the reference samples' values. The results for symmetry, separation, and resolution were all in agreement with the reference samples. The methods used to separate and identify Phenylephrine, cetirizine, loratadine, montelukast, and Ebastine in human plasma were found to be selective, effective, hardy, affordable, environmentally friendly, and reproducible, according to the authors. The selectivity of the SPE technique was validated by the absence of any secondary signal in the plasma samples. Additionally, there was no evidence of these drugs degrading in the plasma sample. This is the initial report on the simultaneous isolation and identification of these eight medications. The well-known SPE and UFLC techniques were successfully used to monitor these drugs in human plasma. Therefore, these drugs can be detected in any plasma sample using SPE or UFLC methods.

Systematic Method Development and Validation of Paclitaxel and Tamoxifen by RP-HPLC for Simultaneous Estimation in Nanoformulations

Background: Paclitaxel (PTX) is well known anticancer drug used for treatment of a wide range of cancers. Tamoxifen (TMX) is a gold-standard drug for the treatment of breast cancer. They show synergistic action against breast cancer. Quantitative analytical methods are still not available for simultaneous quantification of these drugs. So for the first time, we developed and validated a new systematic analytical technique for simultaneous estimation of PTX and TMX in nanoformulations. Objective: Systematic method development and validation of Paclitaxel and Tamoxifen by RP-HPLC for simultaneous estimation in nanoformulations. Methods: PTX and TMX were successfully separated and quantified using RP-HPLC. The detection was done based on the isobastic point of both drugs. Thermo Scientific Company's C18 column, measuring 2.5 cm × 4.5 cm x 5 µm, was utilized for separation. A 50:50 (vol/vol) ratio of ACN: Phosphate buffer solution (pH 3.0) was employed as the mobile phase, with a flow rate of 1 mL/minute. The detection was done at 235nm. The method was developed and validated as per the criteria. The developed method was then evaluated for applicability by detecting both analytes in prepared SLN and LPHNPs. Results: The well-resolved separate peaks of both analytes were found and distinct RT for PTX and TMX. The linear relationship of both the analytes against concentration was found over the concentration range of 0.25-9 µg/mL. The PTX RT was 10.358 minutes and that of TMX was 12.57 minutes. Every criterion for method validation fell within the acceptable range. The method is precise with inter-day and intra-day precision and shows a %RSD of < 2%.

Electrochemical Determination of Dopamine with a Carbon Paste-Lanthanum (III) Oxide Micro-Composite Electrode: Effect of Cetyl Trimethyl Ammonium Bromide Surfactanton Selectivity.

This paper presents a new application of a lanthanum oxide (III)-modified carbon paste electrode (LaOX/CPE) for dopamine (DP) detection in the presence of ascorbic acid (AA). The presence of cetyl trimethyl ammonium bromide (CTAB) facilitated the LaOX/CPE electrode's ability to detect DP amidst AA interference, resulting in a substantial 70.0% increase in the anodic peak current for DP when compared to the unmodified carbon paste electrode (CPE). CTAB enabled clear separation of the anodic peaks for DP and AA by nearly 0.2 V, despite their initially overlapping potential values, through the ion-dipole interaction of AA and CTAB. The electrode was characterized using cyclic voltammetry (CV) and energy-dispersive spectroscopy (EDS). The method demonstrated a detection limit of 0.06 µmol/L with a relative standard deviation (RSD) of 6.0% (n = 15). Accuracy was assessed through the relative error and recovery percent, using urine samples spiked with known quantities of DP.

Phenolic profiles of Australian monofloral Eucalyptus, Corymbia, Macadamia and Lophostemon honeys via HPLC-DAD analysis

Australian honey samples from four botanical genera (Lophostemon, Eucalyptus, Macadamia and Corymbia) were investigated for their phenolic content. An improved phenolic extraction and high-performance liquid chromatography-diode array detection (HPLC-DAD) analysis method allowed for the rapid and reliable identification of phenolic compounds. A concentrated liquid-liquid extraction method with an acidified aqueous solution and acetonitrile was optimised to isolate phenolic compounds from the honey matrix. The concentrated extraction method improved sensitivity and permitted the identification of phenolics present at low concentrations (LOD: 0.012–0.25 mg/kg and LOQ: 0.040–2.99 mg/kg). The optimised HPLC-DAD chromatographic conditions gave stable retention times, improved peak separation and allowed for the inexpensive detection of each of the 109 phenolic compounds at their maximum absorbance wavelength. Out of the 109 phenolic compounds included in this study, 49 were identified in the Australian honeys tested. Furthermore, 25 of the 49 compounds were determined to be markers specific to honey floral origin.

Polydopamine functionalized FeTiO3 nanohexagons for selective and simultaneous electrochemical determination of dopamine and uric acid.

Herein we report the simultaneous detection of dopamine (DA) and uric acid (UA) using polydopamine (PDA) functionalized FeTiO3 nanohexagons. The nanohexagons were hydrothermally synthesized and subsequently functionalized with PDA in a Tris-buffer solution. The PDA functionalized nanostructure was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR), respectively. The SEM and TEM investigations revealed the presence of FeTiO3 nanohexagons along with a peripheral coating of PDA over the nanostructures. The XRD pattern confirmed the formation of the ilmenite structure, while the chemical structure was investigated through XPS and FTIR respectively. Using cyclic voltammetry (CV) the efficacy of FeTiO3-PDA electrode was evaluated toward DA oxidation. The enhanced activity of the functionalized electrode in DA oxidation, as compared to the untreated FeTiO3, may be attributed to the significant presence of hydroxyl, amine, and imine functional groups over the polymer layer. Differential pulse voltammetry (DPV) was utilized for the detection of DA and UA. With a linear range of 50 μM to 250 μM, the detection limits of 0.30 μM and 4.61 μM were determined for DA and UA, respectively. The peak separation of 263 mV between DA and UA demonstrates the sensor's remarkable selectivity. In addition, the study displayed the ability to detect both DA and UA simultaneously, and the validity of the sensor was evaluated in serum samples, respectively.

Racetrack FAIMS for High-Resolution and High-Sensitivity Characterization of Peptide Conformers.

A racetrack field asymmetric waveform ion mobility spectrometry (r-FAIMS) device, which consists of both cylindrical FAIMS (c-FAIMS) and planar FAIMS (p-FAIMS) sections with a 1 mm gap width, was developed and applied for high-resolution and high-sensitivity exploration of conformational diversity for peptides. The optimal operating conditions of r-FAIMS were systemically studied, and the performance of the fully optimized r-FAIMS was compared to a previously developed p-FAIMS in detail by using pure nitrogen as the FAIMS carrier gas. Relying on the ion focusing effect in the c-FAIMS section, the intensity of the FAIMS spectrum for doubly charged bradykinin ions acquired by using r-FAIMS is ∼8.5-fold higher than that acquired by using p-FAIMS under the same resolving power/resolution condition, implying about an order of magnitude better sensitivity of r-FAIMS. In addition, the peak separation resolution of r-FAIMS was ∼1.70-fold higher than p-FAIMS under a similar sensitivity condition for doubly charged bradykinin ions. Due to a reduced gap width of the newly designed r-FAIMS (1 mm) as compared to the previously developed p-FAIMS (1.88 mm), r-FAIMS can operate at a much higher separation field with a similar FAIMS dispersion voltage (DV) to gain significantly higher resolving power. For triply charged syntide 2 ions, the resolving power of r-FAIMS can easily exceed 120 at -3.5 kV DV by using pure nitrogen as the FAIMS carrier gas as compared to 44.2 resolving power obtained by using p-FAIMS at -4.0 kV DV. All of the experimental results have confirmed that r-FAIMS can perform structural characterization of biomolecules with both high resolution and high sensitivity.

Stilbenes in Carex acuta and Carex lepidocarpa.

Stilbenes in the roots of Carex acuta and Carex lepidocarpa were studied. Root samples were extracted with 100% methanol and analyzed by HPLC and LC-MS. In this way, trans-resveratrol dimers (m/z 455 Da [M + H]+), trimers (m/z 681 Da [M + H]+) and tetramers (m/z 907 Da [M + H]+) were identified in the extracts. Using LC-NMR in stop-flow mode, pallidol and trans-ε-viniferin as dimers were identified. After the separation of individual peaks and their measurement by 1H NMR, cis and trans-miyabenol A as a tetramer and cis-miyabenol C as a trimer were identified. In the case of miyabenol A, it is a chromatographically inseparable mixture of cis and trans isomers in the ratio of 2:3 according to 1H NMR measurement. In the case of cis-miyabenol C, the Z-trans-trans-miyabenol C configuration was confirmed. The remaining unidentified peak with a practically identical UV-VIS spectrum to that of cis-miyabenol C is most likely another isomer of miyabenol C.

Electrochemical Detection of Bisphenol a By Modified Gold Electrode with Ternary Quantum Dot Metal Organic Framework Composites

Modified gold electrode with Metal-organic framework (MOFs), ternary quantum dots (TQDs) and their composite (TQDs@MOFs) were as electrochemical sensor to determine bisphenol A (BPA). A comparative electrochemical study of the MOFs, QDs and QDs@MOFs reveals that the composite (QDs@MOFs) have the highest conductivity, largest effective surface area, lowest peak potential separation (∆Ep) and the highest oxidation peak current. Under optimal conditions and wide range of BPA concentrations, the ternary quantum dots metal organic frameworks were a better sensor for bisphenol A with 0.488 nM limit of detection and 1.473 nM. limit of quantitation in comparison to metal organic framework and quantum dots. The results show that QDs@MOFs responded remarkable to BPA and could be adapted a practical and efficient efficient sensor for the determination of BPA

Effective Non-Precious Metal Oxide Supported Carbon as a High Performance Bifunctional Electrocatalyst for All Vanadium Redox Flow Batteries

As one of the most promising electrochemical energy storage systems, vanadium redox flow batteries (VRFBs) have received increasing attention owing to their attractive features for large-scale storage applications. However, their high production cost and relatively low energy efficiency still limit their feasibility. One of the critical components of VRFBs that can significantly influence the effectiveness and final cost is the electrode. Therefore, the development of an ideal electrocatalyst with low cost, large active surface area, good chemical stability, and excellent electrochemical activity toward the VO2+/VO2 + and V2+/V3+ redox reactions is essential for the design of VRFBs. Hence, we prepared a stable, high catalytic activity and uniformly distributed non-precious metal oxide nanoparticles on the surface graphene sheets via two step routes, hydrothermal followed by annealing at optimum temperature for VRFB applications. Among the samples, the prepared electrocatalyst shows the best electrochemical activity with lowest peak potential separation and highest peak current density toward VO2 +/VO2+ and V2+/V3+ redox reactions. This observation is due to the synergistic effects related to the presence of excess oxygen vacancies on the metal oxide, the high content of oxygen functional groups, and the high electrical conductivity of the graphene sheets. Hence, the prepared electrocatalyst grown on the surface of graphite felt (GF) support demonstrates the optimal electrochemical activity with the energy and voltage efficiencies of 76.8% and 80.9%, respectively, which are much greater than those of the 59.8% and 63.2% attained from pristine GF at 100 mA cm–2. Moreover, the electrode presented good stability and durability in acidic electrolyte during long-term operations for 100 cycles at a higher current density of 100 mA cm–2.

Sodium Polysulfides As Catholytes for Redox Flow Batteries

Redox flow batteries based on sodium polysulfide (Na2Sx) show promise due to sodium's high solubility in organic solvents (e.g., diglyme. However, when x is lower than 5, sodium polysulfide exhibits low solubility (less than 0.1 molal), limiting the nominal capacity of this redox-active material. Sodium phosphorothioate complexes, Na2P2Sx, have been reported as an alternative to Na2Sx. Incorporating phosphorus into the polysulfide structure improves their solubility in organic solvents, specifically in diglyme.This presentation will describe the synthesis and characterization of sodium phosphorothioate complexes (Na2P2Sx, where x = 6, 7, 8, and 9) for nonaqueous redox flow batteries. The structure of these materials is explored using 31P NMR and 23Na NMR spectroscopy, Raman spectroscopy, and X-ray diffraction analysis. Overall, 31P NMR results indicate that P5+ is tetrahedrally coordinated in all structures and that Na-P-S compounds have a common PS3- moiety. Ongoing efforts are aimed at providing more precise assignments to the 31P bands and correlating these findings with complementary structural information obtained from 23Na NMR and Raman spectroscopy.Electrochemical properties of sodium polysulfide and sodium thiophosphate catholytes, specifically Na2S8 and Na2P2S8, were also compared using CV. The voltammogram of Na2S8 revealed two clear redox reactions in the 1.5-3 V range vs. Na/Na+ due to a multi-step electron transfer process involving the S2-/S0 redox center. In contrast, Na2P2S8 exhibited a larger peak separation (~2 V) and lower peak currents at a given scan rate, potentially indicating a significant activation barrier associated with the rearrangement of the thiophosphate’s polyanionic structure during reduction/oxidation. Despite the substantial voltage hysteresis, Na2P2S8 displayed stable cycling performance, with a slight increase in peak current after 100 cycles. This behavior is consistent with measurements on RFBs containing a Na2P2Sx catholyte, where an electrode activation process increased the cell’s reversible capacity, likely due to subtle changes in the electrode’s surface chemistry during repeated oxidation/reduction. Finally, preliminary flow cell measurements on Na2P2S7 catholyte show reversible voltage profiles after the formation step with deep discharge. Overall, this presentation demonstrates that Na-P-S catholytes represent a promising material for high energy, low-cost redox flow batteries.AcknowledgementsThis research was conducted at Oak Ridge National Laboratory, managed by UT Battelle, LLC, for the U.S. Department of Energy (DOE) and is sponsored by the U.S. Department of Energy through the Energy Storage Program in the Office of Electricity.

Novel nanostructured transparent Na2O–Al2O3–SiO2 carnegieite-based glass ceramics with high crystallinity

Developing next-generation cover glasses with high crystallinity and transmittance, such as transparent nanocrystalline Na2O–Al2O3–SiO2 (NAS) glass, has proved highly challenging. Herein, we propose a novel nanostructured transparent NAS glass–ceramic with high crystallinity (65 %) and transmittance (91 %) owing to the involved separation of crystallization peaks and the diffusion barrier properties of ZrO2. Compared with untreated glass, this glass-ceramic shows a considerable increase in hardness (from 5.18 to 7.15 GPa, i.e. >38 %). With the increased crystallinity, no substantial reduction in transmission is detected and the crystal type and size can be effectively controlled by the limitation of ZrO2. Hence, the findings project a novel method for creating high crystallinity and transmittance, providing new directions for transparent NAS glass–ceramic.

Stability-indicating green HPLC method for fixed-dose tablets containing remogliflozin etabonate and teneligliptin: an AQbD approach

Background In June 2021, the Central Drug Standards Control Organization approved a fixed-dose combination tablet containing remogliflozin etabonate (100 mg) and teneligliptin (10 mg) to manage type II diabetes. Objective This study aims to develop a stability-indicating RP-HPLC method for quantifying remogliflozin etabonate and teneligliptin in tablet formulations via analytical quality by design (AQbD) principles. Methods Risk assessment, Plackett–Burman design, and central composite design were employed to understand the impact of independent variables on critical analytical attributes. The stationary phase was a HyperClone BDS C18 column, and the mobile phase consisted of acetonitrile and phosphate buffer (20 mM, pH 5) at a 45:55% (v/v) ratio. Results The method, validated per ICH Q2 (R1), resulted in retention times of 3.395 and 12.308 min for teneligliptin and remogliflozin etabonate, respectively. Forced degradation studies confirmed robustness, with clear peak separation and no interference from degradation products. The AGREE score of 0.65 supports its green applicability for tablet analysis in quality control. Conclusion The AQbD-assisted RP-HPLC method developed in this study offers environmental friendliness, efficient separation with well-defined peaks, and simple mobile phase combination.

Quantifying Covalency and Environmental Effects in RASSCF-Simulated O K-Edge XANES of Uranyl.

A RASSCF approach to simulate the O K-edge XANES spectra of uranyl is employed, utilizing three models that progressively improve the representation of the local crystal environment. Simulations successfully reproduce the observed three-peak profile of the experimental spectrum and confirm peak assignments made by Denning. The [UO2Cl4]2- model offers the best agreement with experiment, with peak positions (to within 1 eV) and relative peak separations accurately reproduced. Establishing a direct link between a specific electronic transition and peak intensity is complicated, as a large number of possible transitions can contribute to the overall peak profile. Furthermore, a relationship between oxygen character in the antibonding orbital and the strength of the transition breaks down when using a variety of orbital composition approaches at larger excitation energy. Covalency analysis of the U-O bond in both the ground- and excited-state reveals a dependence on the crystal environment. Orbital composition analysis reveals an underestimation of the uranium contribution to ground-state bonding orbitals when probing O K-edge core-excited states, regardless of the uranyl model employed. However, improving the environmental model provides core-excited state electronic structures that are better representative of that of the ground-state, validating their use in the determination of covalency and bonding.

Carbon cloth core with a PEDOT decorated TiO2 shell for degradation of emerging organic contaminants and enhanced vanadium redox flow batteries

In this study, carbon cloth (CC) was enrobed with a TiO2 layer (CC@TiO2) and then decorated with poly(3,4-ethylenedioxythiophene) (PEDOT, CC@TiO2-PEDOT). The XRD, Raman, XPS, and EDS results confirmed the successful preparation of the targeted materials, and SEM images revealed the targeted morphology. According to the UV–vis and PL analysis, the CC@TiO2-PEDOT exhibits wide and strong photoabsorption across the UV–vis spectrum, and the photogenerated charge carriers have a long lifespan and low recombination rate. The photocatalytic assessment revealed that CC@TiO2-PEDOT was more efficient than CC@TiO2 and CC@PEDOT in degrading both benzotriazole and 2-hydroxybenzothiazole, however, 2-hydroxybenzothiazole was more stable than benzotriazole. The superoxide anion radicals, holes, and/or hydroxyl radicals of CC@TiO2-PEDOT played pivotal roles in the photocatalytic degradation of benzotriazole. After the photocatalytic process, the benzotriazole solution was safe to use. The CC@TiO2 and CC@TiO2-PEDOT exhibited a superior performance as a potential cathode for vanadium redox flow batteries (VRFBs) and effectively mitigated the parasitic influence of the hydrogen evolution reaction (HER). CC@TiO2 and CC@TiO2-PEDOT displayed significantly smaller peak separation of 94 and 62 mV, at a scan rate of 5 mV/s, respectively, and a higher suppression for HER in comparison to CC or CC@PEDOT. The performance of the CC@TiO2 and CC@TiO2-PEDOT electrodes manifests their high reversibility for the V(II)/V(III) redox reaction. This research underscores the multifaceted potential of CC@TiO2-PEDOT as a promising material for addressing water purification challenges and advancing VRFBs for sustainable energy applications.

Separate Peaks: Reasons to Reject Derek Parfit’s Views about Theoretical Moral Convergence

Abstract Derek Parfit argued that “Kantians, Contractualists, and Consequentialists … are climbing the same mountain on different sides.” By that he meant that when their views are properly developed, they will converge. One reason to reject his substantive view, however, is that he could not see how to account for the deontological intuition that it is very hard to justify using people as a means. Matthew Oliver offers a clever way for evaluator-neutral consequentialists like Parfit to account for that intuition. But Oliver’s account runs into two problems: the axiology itself is problematic, and it seems inconsistent with other deep deontological intuitions. I offer a different development of contractualism that accounts for the relevant deontological intuitions, but it’s a fundamentally different “mountain.” Convergence is not in sight, but one can still hope that all climbers will eventually migrate to the better mountain.

SIMULTANEOUS DETERMINATION OF ASCORBIC ACID, URIC ACID, AND DOPAMINE ON CARBON NANOTUBE PASTE ELECTRODE

Background: Ascorbic acid (AA), uric acid (UA), and dopamine (DA) play crucial roles in human metabolism. These substances coexist in biological fluids, and their levels are directly associated with various pathologies. A significant problem encountered in the direct and simultaneous electrochemical detection of AA, UA, and DA is that these species present very close oxidation potentials on most electrode materials, leading to an overlap in the voltammetric response. Aim: The main goal of this work was to determine the concentration of AA, UA, and DA in a natural water sample on a carbon nanotube paste electrode (CNTPE). Methods: All voltammetric measurements were performed on a µAutolab potentiostat/galvanostat (Metrohm) connected to an electrochemical cell of three electrodes: working, reference (Ag/AgCl, KCl3.0M), and auxiliary (platinum). The working electrode was handmade in our laboratory. The following proportions were used to prepare the paste: 50% CNT + 50% mineral oil and 65% CNT + 35% mineral oil. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used for the electroanalytical study. Results: The linear ranges for the simultaneous determination of AA, DA, and UA by DPV were: 0.45 – 1.0 mM, 50 – 200 ?M, and 10 – 90 ?M, respectively. The LODs of the proposed method for AA, DA, and UA were: 7.97 mM; 8.57 ?M, and 5.96 ?M, respectively. The relative standard deviations (RSD) were 4.6, 2.8, and 1.6% for 0.45 mM of AA, 50 ?M of DA, and 50 ?M of UA. Discussion: The oxidation mechanism of: AA, UA, and DA is a process that involves two electrons and 2 protons. Electrochemical detection of DA in the presence of high levels of AA on carbon-based electrodes becomes difficult due to the catalytic oxidation of AA by DA. For the three molecules, AA, UA, and DA, it is observed that the oxidation peak currents increased with increasing concentration. Conclusions: CNTPE allowed the separation of the oxidation peaks of the ternary mixture of AA, UA, and DA by cyclic voltammetry and, when associated with DPV allowed the simultaneous quantitative determination of AA, UA, and DA.

Electrochemical performance of MXene/Fe3O4 composite derived from recycled carbon for vanadium redox flow battery

MXenes are emerging 2D materials that have demonstrated excellent combined metallic electrical conductivity and hydrophilicity. They have been extensively studied in applications like energy storage, catalysis, optoelectronics, and so on. In this work, the carbon sourced from carbon soot extracted from fossil fuel combustion wastes was used to produce Ti3C2Tx MXene for the first time. The recyclable carbon-derived MXene/iron oxide (Fe3O4) composites with different concentrations of Fe3O4 were synthesized via a hydrothermal route. The successful synthesis of the MXene/Fe3O4 composites was confirmed by the SEM, HRTEM, EDX, UV–Vis, XRD, FTIR, and XPS analyses. Electron images morphologically revealed the existence of Fe3O4 within the as-synthesized composites, while UV–Vis spectra detected the surface plasmon resonance peaks of MXene and Fe3O4, respectively. The XRD spectra identified the crystalline structure of MXene at 5.7° (002) and 25.3° (006), as well as the magnetite Fe3O4 at 18.2° (111) and 38.2° (311), which aligned well with the presence of Ti-O and Fe-O bands observed in the FTIR data. The XPS study also confirmed the presence of the Fe element within the composites. The electrochemical performance of composite as electrode material towards the cathode VO2+/VO2+ redox reaction was investigated. The synergistic effect of both MXene and metal oxide improved the electrode kinetic activity towards the redox reaction, as evidenced by the voltage peak separation (ΔE) and the ratio of peak currents (IO/IR) values determined in cyclic voltammetry (CV), and the charge transfer process probed by electrochemical impedance spectroscopy (EIS). The specific capacity of the battery with the composites was increased along with the improvement of retention strength. The MXene/Fe3O4 5 wt% composite displayed the highest electrochemical catalytic activity with the lowest ΔE (124 mV), IO/IR of about 1, producing specific capacities of 10.2 Ah L-1 and energy efficiency of 70.1 %. The nature of MXene and Fe3O4, morphological features, and higher surface area of composites increased the kinetic activity of the electrode, enabling the composites to be potentially applied in the vanadium redox flow battery (VRFB) system.