Search Results (112)

Detecting small molecules in biological fluids is essential for diagnosing diseases, monitoring therapy, and studying how the body works. Traditional biosensing methods—such as amperometric, optical, or piezoelectric systems—offer excellent sensitivity but often rely on complex instruments, additional reagents, or time-consuming sample preparation. Potentiometric biosensors, by contrast, provide a simpler, low-power, and label-free alternative that can operate directly in biological environments. This review explores the latest progress in potentiometric biosensing for small-molecule detection, focusing on new solid-contact materials and advanced sensing membranes and compact device designs. We also discuss key challenges, including biofouling, matrix effects, and signal drift, together with promising strategies such as antifouling coatings, nanostructured interfaces, and calibration-free operation. Finally, we highlight how combining potentiometric sensors with artificial intelligence, digital data processing, and flexible electronics is shaping the future of personalized and point-of-care diagnostics. By summarizing recent advances and identifying remaining barriers, this review aims to show why potentiometric biosensors are becoming a powerful and versatile platform for next-generation biomedical analysis. Full article

Proton binding (i.e., charging) isotherms of halloysite nanotubes (HNT) were determined from cycled acid-base potentiometric titrations in KCl solution at constant ionic strengths (0.01, 0.10, 1.00 mol dm⁻³). The isotherms measured in the pH cycle from 3 to 11 and back exhibit a pronounced hysteresis with respect to the direction of pH change, which is accurately reproducible when the cycle is repeated. The hysteresis is absent if the cycled titration is performed within a narrow pH range between 5 and 9. These results align with the dissolution rates of alumina and silica, which form the two surfaces of the rolled kaolinite sheet in HNT, and clearly point to reversible partial dissolution-deposition processes in the HNT interior during a titration cycle, outside the above pH range (alumina dissolution below pH ≈ 5 and silica dissolution above pH ≈ 8.5). In the studied titration experiments, these processes produce partially dissolved surface-bound, rather than completely dissolved species (reversible surface etching). Under the applied conditions, reversible surface etching is less pronounced in the acidic part of the titration cycle. Charging isotherms recorded in the decreasing pH titrations at varied ionic strength exhibit a common intersection point very close to zero charge (point of zero charge) around pH ≈ 8.1, characteristic for an amphoteric solid surface. These isotherms were reasonably well fitted by applying the surface protonation model in the HNT interior, which invokes the Stern model of the electric double layer (EDL), by summing the surface charges calculated for alumina and silica as separate components (surfaces). The model surface charge isotherms for alumina surface in the HNT interior exhibit a point of zero charge at pH = 9.0, while the silica surface has a negative charge above pH > 8.5, which is in very good agreement with the values reported in the literature: as for these two surfaces, thus for kaolinite nanoparticles. The best-fit protonation site density for both surfaces is equal to 8.0 nm⁻², while the best-fit intrinsic pK_a for alumina and silica surfaces of HNT are equal to 9.0 and 8.5, respectively. The pH-dependence of electrophoretic mobility, measured by means of electrophoretic light scattering, reveals a more acidic behavior of the outermost silica surface than within the inner HNT phase, which is consistent with the literature result reported for kaolinite. The results reported herein confirm that the inner and outer surfaces of the HNT are oppositely charged below pH < 8.0 and negatively charged above that value, and importantly, they reveal new details about the protonation affinities and EDL parameters at active surfaces of HNT, important for the colloidal stability of HNT suspensions and the functionalization of HNT through the electrostatic binding of active molecules. Full article

For the first time, an alternative and sustainable approach is reported using phenyl-2-pyridyl ketoxime (PPKO) as a selective extracting agent for the recovery of Cu(II) from alkaline solutions in the presence of tartrate ions. The advantages relative to conventional processes carried out in acidic media are outlined. Through potentiometric and spectrophotometric analyses, the sequential formation of a 1:2 metal cation–ligand Cu(II)-(PPKO)₂ complex was identified as the predominant species in alkaline aqueous solutions. The high removal capacity of the extractant for Cu(II), as assessed from liquid–liquid extraction, and its efficient performance are comparable to widely used commercial extractants. Thermodynamic studies of the complexation between the copper(II) ion and PPKO demonstrated that the process exhibits an endothermic character. A progressive decrease in the performance of the extractant was observed after reuse without a regenerative treatment. This deterioration was partially reversed through a controlled reprotonation process using an acetate buffer solution. Overall, the results support the potential of PPKO as an effective and selective alternative ligand for hydrometallurgical applications in alkaline medium. Full article

Mining activities have long-term impacts on the environment even after the active stage. Historical mines developed in the 19th and 20th centuries for tin, copper, and mainly iron ore are located in the Pitkäranta area (Karelia, Russia). These objects are considered in our research as natural–anthropogenic sites of long-term water–rock interaction. Waters from flooded mines are the subject of this research. Redox conditions, pH, dissolved oxygen content, conductivity, and water temperature were determined during field work. The chemical composition of natural waters was determined by ICP-MS, ICP-AES, ion chromatography, potentiometric titration, and spectrophotometry. Our investigation showed that the mine waters are fresh and predominantly calcium–magnesium hydrocarbonate; most samples showed elevated sulfate ion contents. Circumneutral pH values and the absence of extremely high concentrations of heavy metals indicate neutral mine drainage. However the calculation of the accumulation coefficient showed the highest levels for siderophile elements relative to the corresponding data of the geochemical regional background. Moreover, zinc has the highest content in the series of heavy metal(loid)s considered. The maximum concentration of zinc was determined in the water of one of the shafts of the Lupikko mine, i.e., 5205 µg/L. The accumulation of heavy metals occurs in the process of long-term interaction of water–rock–organic matter under conductive redox conditions. Overall, the research highlighted the relevance of investigating the geochemistry of historical mines in the Pitkäranta area both from the perspective of environmental safety and the preservation of mining sites for scientific and educational purposes. Full article

The acid number evaluates the degree of deterioration of lubricating oil. Existing methods for evaluating the performance degradation of lubricating oils are mostly based on the detection of traditional physical and chemical indicators, which often only reflect a single dimension of the degradation process, thus affecting the accuracy and repeatability of the results. Integrating multi-dimensional information can more comprehensively reflect the essence of degradation, which can improve the accuracy and reliability of the evaluation results. Mid-infrared spectroscopy is an effective means of monitoring the acid number. In this study, a combination of infrared spectroscopy quantitative analysis and chemometrics was used. The oil sample data was divided into training set and validation set by the Kennard–Stone method. In the experiment, a Fourier transform infrared spectrometer equipped with an attenuated total reflection accessory (ATR-FTIR) was used to collect spectral data of the samples in the wavenumber range of 1750–1700 cm⁻¹ (this range corresponds to the characteristic absorption of carboxyl groups and is directly related to the acid number). Meanwhile, a G20S automatic potentiometric titrator was used to determine the acid number as a reference value in accordance with GB/T 7304. The study compared various preprocessing methods. A regression prediction model between the spectra and acid number was established using partial least squares regression (PLSR) within the selected wavenumber range, with the root mean square error of cross-validation (RMSECV), root mean square error of prediction (RMSEP), and coefficient of determination (R) as evaluation indicators. The experimental results showed that the PLSR model established after preprocessing with second derivative combined with seven-point smoothing exhibited the optimal performance, with an RMSECV of 0.00505, an RMSEP of 0.14%, and an R of 0.9820. Compared with the traditional titration method, this prediction method is more suitable for real-time monitoring of production lines or rapid on-site screening of equipment. It can in a timely manner warn of the deterioration trend of lubricating oil, reduce the risk of equipment wear caused by oil failure, and provide efficient technical support for lubricating oil life management. Full article

Renewable fuels produced from animal- and plant-based edible oils have emerged as an alternative to oil and natural gas. Burgeoning interest in renewables can be attributed to the rapid depletion of fossil fuels caused by the global energy demand and the environmental advantages of renewables, specifically reduced emissions of greenhouse gases. An important property of the feedstock that is crucial for the conversion of edible oils to renewable fuels is the total acid number (TAN), as even a small increase in TAN for the feedstock can lead to corrosion of the catalyst in the refining process. Currently, the TAN is determined by potentiometric titration, which is time-consuming, expensive, and requires the preparation of reagents. As part of an effort to promote the use of renewable fuels, a partial least squares regression method with orthogonal signal correction to remove spectral information related to the sample background was developed to determine the TAN from the mid-infrared (IR) spectra of the feedstock. Digitally blended mid-IR spectral data were generated to fill in regions of the PLS calibration where there were very few samples. By combining experimental and digitally blended mid-IR spectral data to ensure adequate sample representation in all regions of the spectra–property calibration and better understand the spectra–property relationship through the identification of sample outliers in the original data that can be difficult to detect because of swamping, a PLS regression model for TAN (R² = 0.992, cross-validated root mean square error = 0.468, and bias = 0.0036) has been developed from 118 experimental and digitally blended mid-IR spectra of commercial feedstock. Thus, feedstock whose TAN value is too high for refining can be flagged using the proposed mid-IR method, which is faster and easier to use than the current titrimetric method. Full article

This work studies the effect of mesostructured silica–zirconia–tungstophosphoric acid (SiO₂-ZrO₂-TPA) composites used as catalysts in the synthesis of nifedipine by the Hantzsch methodology. The selectivity for nifedipine is determined, along with that of secondary products that may form depending on the reaction conditions. The materials were synthesized via the sol–gel method and characterized by N₂ adsorption–desorption isotherms, infrared spectroscopy (FT-IR), ³¹P solid-state nuclear magnetic resonance (NMR-MAS), X-ray diffraction (XRD), thermogravimetric analysis (TGA), X-ray photoelectron spectra (XPS), and potentiometric titration. The characterization results from the XPS spectra showed that as the Si/Zr ratio drops, the Si-O-Si signal size decreases, while the Zr-O signal size increases. Characterization by titration indicated that an increase in the total acidity of the material, resulting from support modification with tungstophosphoric acid (H₃PW₁₂O₄₀, TPA), enhances the reaction yield. The catalytic activity in the solvent-free Hantzsch reaction was evaluated under thermal heating and microwave irradiation. The experiments conducted at 80 °C achieved a maximum yield of 57% after 4 h of reaction using the Si20Zr80TPA30 catalyst (50 mg), while by microwave heating, the yield significantly improved, reaching 77% in only 1 h of reaction. This catalyst exhibited stability and reusability without significant loss of activity up to the third cycle. Depending on the type of material and the reaction conditions, it is possible to modify the selectivity of the reaction, obtaining a 1,2-dihydropyridine isomeric to nifedipine. Reaction intermediates and other minor secondary products that may be formed in the process were also evaluated. Full article

The effects of acid and alkali pretreatments on the physicochemical and textural properties of Macrocystis pyrifera were evaluated to assess its potential for removing recalcitrant organic pollutants from aquatic systems. Untreated (UB), acid-pretreated (A_CPB), and alkali-pretreated (A_LPB) seaweed biomass were characterized using SEM, FTIR-ATR, N₂ adsorption–desorption, and potentiometric titrations. Adsorption isotherms and kinetic studies, using methylene blue (MB) as a model pollutant, were conducted to evaluate removal performance. All biosorbents exhibited Langmuir behavior, with maximum adsorption capacities of 333 mg g⁻¹ (UB), 189 mg g⁻¹ (A_CPB), and 526 mg g⁻¹ (A_LPB). FTIR-ATR and SEM analyses revealed that alkali pretreatment increased the abundance of hydroxyl, carboxylate, and sulfonated functional groups on the seaweed cell walls, along with greater porosity and surface roughness, resulting in enhanced MB adsorption. In contrast, acid pretreatment increased the exposure of carboxylic, amine, and amide functional groups, reducing the electrostatic interactions. The adsorption energy values further supported this, while the intra-particle diffusion model indicated a two-step process involving MB diffusion onto the seaweed surface, followed by diffusion into internal pores. These findings highlight the potential application of Macrocystis pyrifera-based biosorbents in the treatment of wastewater containing recalcitrant organic pollutants. Full article

This study presents a detailed thermodynamic investigation on the protonation behavior of tartronic acid in aqueous solutions of various ionic media, including sodium chloride, potassium chloride, tetramethylammonium chloride, and tetraethylammonium iodide. Specifically, potentiometric measurements were performed at temperatures ranging from 288.15 to 310.15 K and ionic strengths between 0.1 and 1.0 mol dm⁻³ to determine stoichiometric protonation constants in different ionic media. The formation of weak complexes between tartronate and alkaline metal cations was obtained by means of the ΔpK method. Moreover, data were modeled using the Debye–Hückel equation and Specific Ion Interaction Theory (SIT), allowing for the calculation of standard thermodynamic parameters and the assessment of the dependence of protonation constants on ionic strength. Additionally, the protonation behavior of tartronic acid was compared with that of structurally related acids, such as malonic and mesoxalic acids, providing insights into the role of molecular structure in acid dissociation. The results emphasize the significant role of entropic contributions in the protonation process and provide a comprehensive model for the thermodynamic properties of tartronic acid across a wide range of experimental conditions. Full article

Supercapacitors have a better power density than batteries; however, there is room for improvement in energy density. Co₃V₂O₈ nanoparticles were synthesized using the hydrothermal approach, with the reaction duration tuned to enhance energy density. At a 10 h hydrothermal reaction time, bundles of nanowires with void spaces were obtained, demonstrating excellent areal capacitance of 4.67 F/cm², energy density of 94 μWh/cm², and power density of 573 μW/cm² at a current density of 3 mA/cm². With activated carbon (AC) and Co₃V₂O₈ nanoparticles prepared over a 10-h hydrothermal reaction period, an asymmetric supercapacitor (ASC) was assembled. The device performed admirably in terms of energy storage capacity, with an areal capacitance of 781 mF/cm² and a volumetric capacitance of 1.43 F/cm³. The ASC’s cyclic stability demonstrated capacity retention of 83.40% after 5000 cycles. The powering of red LEDs was used to show practical applications. In a 2M KOH electrolyte, the optimized Co₃V₂O₈ electrode demonstrated good electrocatalytic performance for the hydrogen evolution process, with an overpotential of 259 mV at a current density of 10 mA/cm². Overall, water splitting studies revealed a potential of 1.78 V with little potential enhancement after 8 h of Chrono potentiometric stability. As a result, Co₃V₂O₈ nanoparticles prepared at a 10 h hydrothermal reaction time offer excellent electrode materials for energy storage in supercapacitors and electrocatalytic applications for total water splitting. Full article

Wooden panel paintings (WPPs) are among the most significant historical artworks that must be preserved for future generations. Ensuring their long-term conservation requires a comprehensive characterization of their condition, making monitoring an essential process. Thus, the primary objective of this study is to provide a comprehensive overview of the current techniques employed to study support deformations in WPPs, categorizing them into localized and full-field methods. Specifically, we provide information about linear potentiometric transducers, the Deformometric Kit, and Fiber Bragg Grating sensors as techniques that provide information about specific and isolated points on the artwork’s surface. On the other hand, digital image correlation, stereo-correlation, mark-tracking, 3D modeling techniques, and the moiré method, are discussed as techniques that analyze the entire surface or a significant part of the artwork. Each method has advantages and limitations, depending on the type of monitoring needed and the desired information. Nevertheless, these techniques contribute to understanding the behavior of the artworks’ materials under environmental fluctuations or restoration interventions, aiding the development of targeted and effective conservation strategies. Furthermore, this study seeks to evaluate the effectiveness of these methods in various conservation contexts and offers practical guidelines to assist conservators and researchers in selecting the most appropriate approach to support the long-term conservation of these invaluable historical artworks. Full article

Protolytic reactions on the surface of a titania photocatalyst (TiO₂ P25 containing chlorine impurities) were studied using potentiometric and calorimetric acid-base titration. The impurity was removed by either washing or heat treatment. The efficiency of purification was tested by chlorine (TOX) analysis and acid-base titration. Common intersection points of −0.023 and −0.021 mmol/g were obtained for the original and 400 °C heat-treated samples, which are in good agreement with the measured TOX value of 28 mmol/kg. The point of zero charge of the purified sample was determined to be 6.50. Titration data were fitted to simulate protolytic reactions during isothermal calorimetric titrations of purified titania. The evolved heat was measured, and data points were corrected with the heat of mixing and neutralization. The quantity of charged surface species formed in each step of titration was calculated using the parameters from the constant capacitance model fit. The partial molar enthalpy values of the exothermic and endothermic processes of surface protonation (ΔH_pr, −17.47 to −16.10 kJ/mol) and deprotonation (ΔH_depr, 32.53 to 27.08 kJ/mol) depend slightly on the ionic strength of suspensions. The average standard enthalpy of one proton transfer reaction is −23.54 ± 1.75 kJ/mol, which is consistent with the literature. Full article

This work presents a potentiometric readout circuit for a pH-sensing system in an oral healthcare device. For in vivo applications, noise, area, and power consumption of the readout electronics play critical roles. While CMOS amplifiers are commonly used in readout circuits for these applications, their applicability is limited due to non-deterministic noises such as flicker and thermal noise. To address these challenges, the Correlated Double Sampler (CDS) topology is widely employed as a sampled-data circuit for potentiometric readout, effectively eliminating DC offset and drift, thereby reducing overall noise. Therefore, this work introduces a novel potentiometric readout circuit realized with CDS and a switched-capacitor-based low-pass filter (SC-LPF) to enhance the noise characteristic of overall circuit. The proposed readout circuit is implemented in an integrated circuit using 0.18 µm CMOS process, which occupies an area of 990 µm × 216 µm. To validate the circuit performances, simulations were conducted with a 5 pF load and a 1 MHz input clock. The readout circuit operates with a supply voltage range ±1.65 V and linearly reproduces the pH sensor output of ±1.5 V. Noise measured with a 1 MHz sampling clock shows 0.683 µ$V_{rms}$, with a power consumption of 124.1 µW. Full article

This work presents a comprehensive approach for the justification of the reagent regime of coal flotation by investigating the interfacial characteristics of flotation phases with various techniques. For the energy characterization of the surface processes in flotation systems, a method of establishing the components of the specific surface Gibbs energy on the basis of a numerical estimation of surface free energy change during the adsorption of flotation reagents using the Owens–Wendt–Rabel–Kaelble technique was proposed. Using the developed approach, the features of the kinetics of n-hexane sorption on the surface of coal samples were established. The substantiation of differences in the potential mechanisms of the fixation of strictly apolar and aromatic reagents is based on the results of the quantum–chemical modeling of the states of the coal–adsorbate system using the software packages Avogadro and Orca. The simulation shows the possibility of aliphatic and aromatic reagents’ synergetic effects on coal surface hydrophobization. Based on the results of quantum–chemical modeling, it was found that for the physical adsorption of an oxyethylated nonyl-phenol molecule on a molecular fragment of the coal surface, according to the Weiser model, the decrease in the energy of the system was 0.05562 eV, which indicates the high thermodynamic probability of the physical sorption of this compound. The parameters of the Langmuir monomolecular model for the sorption of oxyethylated nonyl-phenol on the surface of the studied coal samples were established. The criterion characterizing the interphase phenomena in the flotation system based on the results of potentiometric studies of the interfacial characteristics, E_f, was proposed. It was found that for the studied values of the flow rate of oxyethylated nonyl-phenol, the highest value of E_f was achieved when the value of the sorption of the reagent equaled 63.99% of the limiting sorption capacity. The performance of the proposed reagents for coal flotation was confirmed by flotation tests. Full article

In the process of a systematic study of the bis-chelate oxime-amide ligands with different polymethylene spacers and their transition metal complexes, two new Ni(II) and Cu(II) complexes of the mhiea₂poh ligand have been isolated, and their molecular and crystal structures determined by single crystal X-ray diffraction. Potentiometric titrations were performed on a range of aqueous solutions in both systems, which allowed the identification of various complex species and afforded their stability constants. ESR spectra of samples with optimised concentrations of complexes in Cu(II)–L–H system were recorded. A distinguishing feature of both systems is the dimerization of anionic pseudo-macrocyclic complexes. The latter is caused either by centrosymmetric hydrogen bonding of the hydroxy group on the propane spacer to the oximato oxygen of the opposing unit or by back-to-back π-stacking of planar complex units. ESR measurements indicated likely coupling of Cu-Cu paramagnetic centres in the dimers. Full article