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This paper carries out a study of an environmentally friendly natural material for creating a carbon-paste electrode and its application for Fe(II) determination. The electrode-active material (iron-containing carbonized keratin waste) was characterized by scanning electron microscopy (SEM), thermal analysis (DTA, TGA), and FT-IR spectroscopy. The advantages of an electrode modified with composite material are a high selectivity coefficient, a sufficiently wide range of linearity of the electrode pH function for iron (II) ions due to the presence of iron (III) oxide in the carbonation product. The analytical characteristics of the electrode containing Fe (III) were determined in the direct potentiometry mode with a relative error of about 8% and the potentiometric titration (chelatometry) mode with a change in the electrode potential of 4.4 mV and a relative error of 0.2%.

The mechanism of phthalic acid, a dicarboxylic acid collector, in flotation separation of fluorite and rare earth (RE) was studied in this paper. The experimental data of flotation show that phthalic acid, as the collector, can realize highly efficient separation of fluorite and rare earth under weakly acidic conditions. The adsorption mechanism of phthalic acid on the surface of fluorite and bastnaesite was analyzed in this paper by means of the zeta potential measurement, the Fourier transform infrared (FT-IR), the X-ray photoelectron spectroscopy (XPS) and the stability constant measurement of active metal ion and phthalic acid coordination complex. According to the zeta potential testing results, the surfaces of fluorite adsorb the collector phthalate ion with negative charge under weakly acidic conditions which, in turn, increases its electronegativity and results in the motion of its potential. After the reaction between phthalic acid and fluorite ores under weakly acidic conditions, the peak of the fluorite ores is found to have significant changes in the FT-IR results, indicating strong chemical adsorption on the surfaces of phthalic acid and fluorite ores. According to the XPS analysis, the peak of benzene ring of phthalic acid is as high as 2% on the surface of fluorite, while no obvious characteristic peak of benzene ring is found on the surface of bastnaesite. According to the pH potentiometric titration results, the stability constant Ktotal of calcium phthalate complex within the acid range is higher than the stability constant Ktotal' of cerium phthalate complex, indicating that the complex generated between phthalic acid and Ca2+ is more stable than the complex generated between phthalic acid and Ce3+. The possible reason is that Ca2+, with the highest reticular density, plays a prevailing role in the octahedron structure of fluorite amidst the acidic media. As the active point of flotation, Ca2+ works with the carboxyl groups of the collector phthalic acid (–C=O–) to form polycyclic calcium phthalate complex.

Dextran-based gels bearing two types of pendant N, N-dimethyl-N-alkyl-N-(2-hydroxypropyl) ammonium chloride groups with different alkyl chain length substituents (C2 and C12/C16, respectively) at the quaternary nitrogen were synthesized and structural characteristics of the compounds were studied by elemental analysis, potentiometric titration, FTIR and NMR spectroscopy. The morphology and size of polymeric microspheres were examined by SEM and their swelling behavior in water was also investigated. The hydrogels were evaluated as sorbents for sodium cholate (NaCA) and sodium deoxycholate (NaDCA) in water and 10 mM NaCl solutions. Different isotherm models (nearest-neighbor-interaction, Langmuir, Freundlich, Dubinin-Raduskevich, Sips and Hill) were used to elucidate the adsorption mechanism and established the characteristics of the most efficient polymeric sorbent. The maximum adsorption capacity of the gels was highly controlled by gel hydrophobicity which enhanced gel-bile salt affinity but decreased binding cooperativity. Swelling porosity, ionic strength and ligand lipophilicity were other factors that also affected the adsorption process. The hydrogel having 25 mol% pendant dodecyl groups retained the maximum amount of bile salts (1051 mg NaCA/g and 1138 mg NaDCA/g). All hydrophobically modified hydrogels revealed a better affinity and strength of binding compared to commercial Cholestyramine®.

New and novel heavy metal ion selective organic-inorganic composite CNTs reinforced polyaniline@Zn-CuO was expediently obtained by the sol-gel method. Conducting monomer, aniline was polymerized by in situ chemical oxidation. The CNT reinforced polyaniline@Zn-CuO was used for the preparation of ion-selective membrane. The prepared membrane was characterized for porosity, swelling, and find suitable to be used for the preparation of modified ion-selective membrane electrode. The prepared electrode was calibrated with different metal ions and found suitable selective for Hg2+ ions. The electrode showed excellent results as the limit of detection (1 × 10−6 M), working conc range (1 × 10−1 M to 1 × 10−6 M), pH working range (3–6), and response time 17 Sec with room temperature stability two and half month while 30.2 mV is the Nerstian slope obtained by per decade change in metal ion concentration of Hg2+. The practical utility of the proposed membrane sensor assembly was tested by its use as an indicator electrode in the potentiometric titrations.

WOx-ZrO2 (ZWx) based catalysts were prepared by equilibrium adsorption in basic condition (pH 10) with W content of 10.5, 19.7 and 27.0 wt.%, using hydrous zirconia [ZrO2(383)] as support. In order to determine the soluble fraction of W species which did not interact with the surface, samples were leached with NH3, dried and re-calcined [ZWx(NH3)y]. The W content was determined by spectrophotometric method, before and after the leaching. All catalysts were characterized by textural analysis (BET), X-ray diffraction (XRD) and Raman spectroscopy; the acidic strength was determined by potentiometric titration with n-butylamine. The catalytic behavior was analyzed for the selective oxidation of diphenyl sulfide (DPS) to diphenyl sulfoxide (DPSO) or diphenyl sulfone (DPSO2) using H2O2 as oxidizing agent. High conversion of DPS (∼100 %) and selectivity to DPSO2 (>90 %) at 60 min of reaction time were obtained for the ZWx series of catalysts. The ZWx(NH3)y series (W content: 3.65, 6.50 and 7.50 wt.%, respectively) also showed high selectivity to diphenyl sulfone but the maximum conversion (∼100 %) was achieved with reaction times longer (30 min) than those of the ZWx (10 min) samples. Polytungstate species strongly interacting with the support, identified by Raman spectroscopy in both series of samples, are considered the active phases.

Mesoporous activated carbon from sunflower shells (SAC) modified with sulfonic acid groups (SACSO3H-XX) was synthesized by grafting the sulfonic groups on the carbon surface to produce novel heterogeneous and reusable solid acid catalysts. The mesoporous carbon was prepared by chemical (H3PO4) and thermal (600 °C) activation of sunflower seed shells. Four materials with increasing SO3H content (SACSO3H-5, SACSO3H-10, SACSO3H-15, and SACSO3H-20) were obtained using rising chlorosulfonic acid:SAC ratios. They were texturally and physicochemically characterized by SEM-EDX, BET, FT-IR, and TGA-DSC. Potentiometric titration with n-butylamine technique was used to evaluate their acidic properties. The results showed that both the acid strength and the number of acid sites increased with the SO3H content in the SACSO3H-XX samples. The FT-IR spectra of SACSO3H-XX samples confirmed the successful functionalization of SAC with the sulfonic acid group. TGA-DSC diagrams of SACSO3H-20 showed that the elimination of the sulfonic groups takes place in the range 250–350 °C. The activity and selectivity of SACSO3H-XX in the esterification reaction of itaconic acid with absolute ethanol to form the diester derivative depended strongly on their acidic properties. Furthermore, the effective separation of the product combined with the use of a recyclable catalyst resulted in a clean and environmentally friendly strategy for the synthesis of diethyl itaconate, a bioproduct of relevance to the biorefinery industry.

A new heteropolyacid, derived from phosphomolybdic acid containing niobium (PNbMo), was synthesized and included in silica, alumina, and silica/alumina matrixes by sol-gel technique, in order to use it as heterogeneous catalyst. The matrixes confer stability to the active phase, good textural and morphological properties. PNbMo and included materials were characterized by 31P-NMR, FT-IR, UV–vis, TGA, SEM, TEM, XRD, N2 physisorption, and potentiometric titration, and tested as catalyst in the sulfoxidation of diphenyl sulfide under suitable conditions. The redox activity was compared with phospomolybdic acid and correlated with the edge energy obtained from UV–vis absorption spectra. The best results in diphenyl sulfide sulfoxidation were obtained with PNbMo-SiAl-4:1 (92% conversion and 95% selectivity at 3 h) and with PNbMo-Si (92% conversion and 94% selectivity at 4 h). The reuse of these catalysts was evaluated.

Porous carbons were obtained from rice husk using two different chemical activation methods and they were investigated as supercapacitors. Their properties were studied using X-ray photoelectron spectroscopy, thermal analysis, potentiometric titration, and nitrogen adsorption isotherm. The specific capacitance measured in both H2SO4 and KOH electrolytes in two-electrode cell was up to ~150 F/g. The activation method used affected the resulting carbons' features. As expected, the dependence of the capacitance on porosity was found. The ash content reached 36 wt.% and that inorganic mater blocked some pores and limited their accessibility to electrolyte ions and increased the charge transfer resistance. Nevertheless, the main ash constituents such as CaCO3, MgCO3, Ca3(PO4)2 (or P2O5), and Fe- and Zn- containing species did not affect the specific capacitance to a large extent. Especially SiO2, even in a relatively large amount (~20 wt.%), did not play a detrimental role in the capacitance behavior. The results showed that in spite of a high ash content, carbon can exhibit a good capacitive performance provided that it has a favorable porosity and is rich in sp2 configurations.

In recent years, chitosan has attracted considerable interest in many fields due to its sufficient charge density under biological, non-hazardous conditions. Since chitosan originates from natural resources and has two different monomer units, its characterization must be carried out in a goal-oriented and precise manner. This work focuses on the characterization of chitosans most important parameters – solubility, crystallinity, degree of deacetylation (DD) and molecular weight – in a simple and convenient way. The DD was determined using Nuclear Magnetic Resonance spectroscopy (NMR), Particle Charge Detection (PCD), Fourier Transform Infrared spectroscopy (FTIR), CHN elemental analysis (CHN-EA) and conductometric/potentiometric titration with special attention to its physical state as solid or liquid. Investigation of DD by FTIR was successfully determined by calculating peak heights, peak areas and peak deconvolution from a linear combination of Gaussian and Lorentzian functions. Asymmetrical flow field flow fractionation with light scattering detection (AF4-LS) was applied in order to calculate molar masses and radii. In addition, pH-potentiometric titrations demonstrated a reproducible displacement of the point of zero charge (PZC) in form of a hysteresis depending on the titration direction. The DD affects the crystallinity, which was determined by deconvolution of the crystalline and amorphous domains.

Electrochemical study to compare the corrosion resistance of three different aluminum alloys (AA8011, AA4017 and AA1200) in organic acid solutions (nitric and acetic acids) was carried out. Polarization technique was used to determine the corrosion behavior of the alloys in the acid solutions, while potentiometric technique was used to study the passivity of the alloys over time. The surface analysis was carried out on the alloys’ surfaces to know the morphological changes that took place on the surface of the alloys using scanning electron microscopy (SEM). Alloy AA4017 showed the least tendency to pit in acetic acid solution with alloy AA8011 showing the highest susceptibility to pitting in the acidic solutions. All the alloys on the other hand showed high tendencies to pit in nitric acid solution. Considering the rate of corrosion of the alloys in both solutions, alloy AA8011 had corrosion rate of 0.0873 mm/yr., which was the highest in acetic acid solution, while alloy AA1200 had the least corrosion rate of 0.0045 mm/yr. in the solution. Meanwhile, alloy AA4017 exhibited the highest corrosion rate of 0.0552 mm/yr. and alloy AA1200 had the least corrosion rate of 0.0126 mm/yr. in nitric acid solution. These results showed that the AA4017 and AA1200 alloys corroded more in nitric acid solution than in acetic acid solution. Potentiometric test results showed the formation of more stable passive films in nitric acid than in acetic acid solution. The SEM micrographs showed pits formation on the alloys in all the acidic solutions.

Chemical speciation plays key role in understanding the physiological and biological aspects of metal ions and ligands in human body. The complexation of essential metal ions with Glycylglycine (GG) and Histamine (Him) in Sodium Lauryl Sulphate (SLS) has been presented in this study. The complexes formed in the present study are M L X H 2 , M L 2 X H 2 and M L X 2 H 3 . The Skewness values in the present study are from 0.05 to 0.84 for Ca(II), 0.03 to 0.93 for Mg(II) and 0.45 to 1.34 for Zn(II) and the χ2 values obtained the present study are ranging from 7.8250.37 for Ca(II), 6.1837.45 for Mg (II) and15.69143.67 for Zn(II). A very low standard deviation in log β values indicates the precision of the parameters. The advanced principles of mathematics and fuzzy logic have been employed to correlate chemical problems, which is called chemo metrics. In the present investigation potentiometer is used for analysis and the results obtained in the study have been processed through Gran plot method, SCPHD is used for best fit chemical model and MINIQUAD75 is used for refinement of results. An experiment has been conducted to understand the distribution of species, effect of surfactant on stability constants of ternary complexes, effect of influential parameters like concentration of alkali, acid, ligands and metal ions on the stability constants.

In this research, five ion selective electrodes for finsatride drug were successfully prepared including: coated wire electrode (CWE), coated graphite electrode (CGE), carbon paste electrode (CPE), carbon paste-carbon nanotube electrode (CPCNT) and carbon paste-nanosilica electrode (CPNS) depending on the formation of finsatride-TPB complex. Furthermore, the Nernastain response was studied by determination of slope and detection limit with the study pH effect on the response for finsatride electrodes and response time. However, the selectivity was calculated with applied the potentiometric method which including: direct, standard addition method and potentiometric titration for pure and pharmaceutical formulation of finsatride. The RSD was 2.82, 1.52, 2.04, 2.27, 1.84, respectively. And the 6.350 × 10-7 , 7.449 × 10-8 , 6.334 × 10-6 , 5.316 × 10-6 and 5.433 × 10-6 M, respectively.

In this work, we describe a novel method to improve the detection limits of the non-classical polymeric membrane ion-selective electrodes (ISEs) which are conditioned with highly discriminated ions instead of primary ions. It is based on a thin-layer ISE membrane with a thickness of 5 μm, which is coated on ordered mesoporous carbon used as solid contact. The diffusion of the primary ion from the surface of the sensing membrane to the bulk of the membrane could be avoided by the proposed thin membrane configuration. Since the detection sensitivity of the non-classical ISEs depends on the accumulation of the primary ion in the interfacial layer of the sensing membrane, a lower detection limit can be obtained. By using the copper ion as a model, the present potentiometric sensor shows a significantly improved detection sensitivity compared to the conventional ISE with a membrane thickness of ca. 200 μm. Low detection limits of 0.29 and 0.53 nM can be obtained in 0.01 and 0.5 M NaCl, respectively. In addition, the proposed sensor exhibits an excellent reversibility by using a neutral proton-selective ionophore incorporated in the thin membrane.

Kinetic models were developed to describe the esterification reaction of lauric acid and ethanol over heterogeneous catalysts, which is a reaction of special interest in the biodiesel production. Vanadium Keggin heteropolyacid was included on a silica framework by sol–gel procedure, using different loadings. The synthesized materials were characterized by FT-IR, XRD, SEM, nitrogen adsorption/desorption isotherms, and potentiometric titration, and tested as solid catalysts in the esterification of lauric acid. Best performance was achieved with SiO2@20PMoV, which was used in the esterification of others fatty acid and alcohols. The reuse was successfully tested in five consecutive runs. Kinetic data using SiO2@20PMoV were obtained at different temperatures (48–78 °C), fatty acid:alcohol molar ratios (4 mmol of lauric acid and 2.5, 5, 10 and 15 mL of ethanol), and catalyst amounts (12.5, 25 and 50 mg). The best heterogeneous models were LH3 (surface reaction as rate-limiting step) and ER3 (desorption of ethyl laurate as rate-limiting step when the adsorbed reactant is lauric acid). The activation energies were 56.1 kJ mol−1 and 64.8 kJ mol−1, and the reaction rate constants at 78 °C were 0.2791 mol g−1 h−1 and 0.0768 mol g−1 h−1 for LH3 and ER3, respectively.

Traditional potentiometric NO3−-selective electrodes suffer from a fundamental limitation of the Nernst slope (59.1 mV/dec at 25 °C) due to the relationship between the potential and the logarithmic of ionic activity. Herein, a coulometric signal readout is proposed instead of the potentiometric response for detection of NO3− based on an ordered mesoporous carbon (OMC)-based solid-contact ion-selective electrode (ISE). The mechanism for obtaining the coulometric signal is based on the electrical double layer capacitance of OMC compensating the potential change at the ion-selective membrane/solution interface during the measurements under the control of a constant applied potential. Under the optimized conditions, the coulometric signal for the OMC-based solid-contact NO3−-ISE shows two linear responses in the activity range of 1.0 × 10−6-8.0 × 10−6 M and 8.0 × 10−6-8.0 × 10−4 M, and the detection limit is 4.0 × 10−7 M (3σ/s). The proposed coulometric response also shows excellent reproducibility and stability in the presence of O2 and CO2 and light on/off. Additionally, the coulometric response shows acceptable and reliable results for detection of NO3− in mineral water as compared to the traditional potentiometric response and the ion chromatography. This work provides a promising alternative signal readout for detection of ions by using solid-contact ion-selective electrodes.

The presence and form of oxygenated functions on carbons lead to significant differences in material properties that impact surface chemistry, catalysis, electronic, and mechanical properties. Titration methodologies, specifically potentiometric and Boehm titrations, classify the types of acidic functions present on carbon materials into broad categories described as carboxylic, lactonic, and phenolic functions based upon the measured or estimated acid dissociation constants (pKa). The accuracy of these methods depends, however, on the estimates for pKa values and suffers when multiple possible species possess similar pKa values. Here, we improve upon past methods by combining potentiometric and chemical titrations, which involves identifying acidic functions by pKa values but also examining how functional groups react with alkaline titrants. Specifically, Bronsted acids like carboxylic and phenolic groups deprotonate reversibly when contacted with alkaline titrant solutions; however, lactonic functions undergo hydrolysis to form carboxylic acids and hydroxyls during identical treatments. Consequently, comparisons between sequential potentiometric titrations can be used to discriminate between functional groups by examining their pKa values but also their reactivity. Tests on probe compounds and functionalized carbon materials show our method successfully distinguishes lactones from other acidic functions on carbon surfaces and suggests the methodology complements other characterization techniques for carbon materials.

Removing heavy metals from aqueous solutions has drawn the attention of scientists due to their serious global health challenges to human society. Thus, it is very important to use an adsorbent with a high removal efficiency of heavy metals and has the advantage of low-cost. In the present work, metal-organic framework with tailored components is very important in attaining the required purpose and expanding the developing applications. Herein, bimetallic Ag-Fe metal-organic framework has been successfully synthesized through a solvothermal method and characterized by Fourier transform infrared spectroscopy, X-ray diffraction, Scanning electron microscopy, Transmission electron microscopy and surface area measurements. Due to the synergistic contribution between Ag and Fe, bimetallic Ag-Fe metal-organic frameworks nanocrystals exhibit enhanced decontamination performance toward the removal of heavy metal ions with ultra-fast adsorption kinetics and high adsorption values. Impressively, an extraordinary Cadmium (II) and Copper (II) adsorption values up to 265 and 213 mg/g, respectively are obtained in bimetallic (0.6:1) Ag-Fe metal-organic framework, which considers the superior adsorbent between the prepared metal-organic frameworks. The surface acidity, examined through the nonaqueous potentiometric titration of n-butylamine, was found to be increased by the formation of a bimetallic metal-organic framework as well as the catalytic activity. Among various Ag: Fe, the ratio (0.6:1) showed the highest acidity and catalytic activity towards the synthesis of 3,4-dihydropyrimidinone. The metal-organic frameworks catalysts were found to maintain their adsorption capacity and catalytic activity even after four-time reusing.

The dehalogenation of gaseous chlorobenzene (CB) to useful intermediates at ambient temperature is desirable. In this study, gaseous CB was dehalogenated to useful intermediates using an electrochemically generated homogeneous low-valent electron mediator in an electroscrubbing column at ambient temperature. A homogenous electron mediator [Ni(I)(CN)4]3− (Ni(I) low-valent) was generated at the cathodic half-cell using a membrane-divided electrolytic cell and quantified by oxidation/reduction potential (ORP) variations with a potentiometric titration. CB removal according to a mediated electrocatalytic reduction (MER) process, was confirmed by the change in electrogenerated Ni(I) from 4.2 mM to 2.8 mM during the degradation of CB. A Fourier transform infrared gas analyzer and chlorine sensor showed that 100% of 15 ppm CB at a 0.2 L min−1 flow rate had been removed by the MER process with CO2 as the gaseous product. At the same time, the phenoxide anion was found in the resulting solutions, which is a starting material in many pharmaceutical industries. The developed method and possible generation of a homogenous electron mediator on CB dehalogenation to useful intermediates at ambient temperature is a practical technology.

The oxidative reaction between lanthanum trichloride and oxide ion was studied in the molten LiCl-KCl eutectic at 773 K by in-situ Raman spectroscopy using an yttria-stabilized zirconia electrode in conjunction with electrochemical methods. The formation of lanthanum oxychloride, LaOCl(s), was confirmed by studying the vibrational properties of crystalline LaOCl and X-ray diffraction analysis. The solubility product of LaOCl in the LiCl-KCl molten eutectic at 773 K is found to be pKsp(LaOCl) = 7.569 ± 0.100, by combining the results of Raman spectroscopy and potentiometric titration with the addition of barium oxide. The use of Raman spectroscopic quantitation of dissolved lanthanum ions in the system allows faster and more accurate determination of the stable phase of lanthanum as well as the solubility product of LaOCl compared with that measured by potentiometric titration only. Based on experimentally obtained pKsp and standard equilibrium potentials, the potential-pO2− phase diagram of lanthanum in the molten LiCl-KCl eutectic was reported.

The adsorption of metal onto archaea could affect metal behavior and bioavailability in hypersaline environments where archaea represent the dominant life form. However, the mechanism and thermodynamics of metal adsorption onto halophilic archaea are not well understood. In this study, Cd adsorption experiments and potentiometric titrations were conducted to model metal adsorption by the halophilic archaeon Halobacterium sp.. Cd adsorption onto the archaeal cells exhibits slow adsorption kinetics, taking 8 h to reach steady-state. The extent of Cd adsorption depends strongly on pCH+ and Cd loading. Desorption of Cd is even slower than adsorption, but exposure of the Cd-adsorbed biomass to high concentrations of cysteine promotes desorption and demonstrates that the distribution of Cd is controlled by reversible adsorption reactions, likely involving sulfhydryl binding of Cd on the cell surface. We conducted potentiometric titration experiments with and without sulfhydryl site blocking to yield a total sulfhydryl site concentration of 91 ± 28 μmol/g within the archaeal cell envelope. Using a combination of the X-ray absorption fine structure analysis results from Showalter et al. (2016) and the Cd adsorption measurements and titration data from this study, we construct a surface complexation model of the Cd adsorption behavior. Because the Cd adsorption behavior is likely similar to that of a range of chalcophilic micronutrients, the importance of Cd-sulfhydryl binding suggests that the production of high affinity sulfhydryl binding sites by the archaea may represent an adaptive strategy for halophiles to obtain metal nutrients in environments in which aqueous metal-chloride complexation dominates the speciation for many metals.

Paper-based microfluidic device was designed with wax-printing to combine potentiometric, fluorimetric and colorimetric detection zones. This newly developed trimodal paper chip has been used for on-site determination of ketamine hydrochloride (KET) as a date rape drug in beverages. The device employed polyaniline nano-dispersion as conducting polymer in ion sensing paper electrodes designed to fit USB plug connector. Carbon dots-gold nanoparticles and cobalt thiocyanate were used in fluorescence and color detection zones, respectively. Cellular phone's camera facilitated the on-site fluorimetric and color detection. The implemented trimodal detection system exhibited specificity for KET detection in the presence of several other beverage interferences i.e., biogenic amines. This innovative sensor brings together analytical figures of merit for effective KET detection in single aliquot of spiked beverages. The proposed paper-based chip also fulfils WHO criteria for point-of-care devices posing the proposed trimodal paper device as an active part for rapid, on-site drug diagnostics and to be applied further for other similar drugs.

This work investigates two new aspects of the biphasic esterification reaction of glycerol (G) and oleic acid (A), i.e. the formation of several oxidation/dehydration co-products and the effect of the ester products as phase transfer agents to accelerate the reaction. Potentiometric titration, FTIR, TG and especially paper electrospray mass spectrometry (PS-MS) were employed to analyze the products. Reactions with different G:A molar ratios (1:0.5, 1:1 and 1:2) without catalyst at 140, 160 and 180 °C showed oleic acid conversions of 50–80% to form the mono, di and triesters with several other by co-products due to dehydrogenation/oxidation of the oleic chain and dehydration of the glycerol moiety identified by PS-MS. The phase transfer autocatalytic effect was investigated by the addition of the oleate esters (2, 4 and 10 wt%) to the reaction. It was observed a strong acceleration of at the initial stage of the process indicating an autocatalysis likely due to a phase transfer effect. The reaction is discussed in terms of three stages. In the initial biphasic Stage 1, oleic acid suffers some dehydrogenation/oxidation and the esterification reaction takes place slowly at the glycerol-oleic acid interface to form mainly the monooleate ester which is an amphiphilic/tensoactive molecule. In the Stage 2, the amphiphilic ester products act as phase transfer agents taking glycerol molecules to the oleic acid phase for the formation of mono and mainly dioleate ester. At the Stage 3 in the presence of relatively high concentration of the tensoactive ester products the reaction becomes homogeneous/monophasic.

The use of a Pt electrode coated with a layer of Nafion has been described in previous works as an attractive way to perform the potentiometric detection of hydrogen peroxide. Despite of the attractive features of this approach, the nature of the non-Nernstian response of this system was not properly addressed. In this work, using a mixed potential model, the open circuit potential of the Pt electrode is shown to be under kinetic control of the oxygen reduction reaction (ORR). It is proposed that hydrogen peroxide acts as an oxygenated species that blocks free sites on the Pt surface, interfering with the ORR. Therefore, the effect of the polyelectrolyte coating can be understood in terms of the modulation of the factors that affects the kinetics of the ORR, such as an increase of the H+ concentration, minimization of the effect of the spectator species, etc. Because of the complexity and the lack of models that accurately describe systems with practical applications, this work is not intended to provide a mechanistic but rather a phenomenological view on problem. A general framework to understand the factors that affect the potentiometric response is provided. Experimental evidence showing that the use of polyelectrolyte coatings are a powerful way to control the mixed potential open new ways for the development of robust and simple potentiometric sensors.

In this study, ultrathin and defect-free graphene (Gr) sheets were prepared through a fluid dynamics–induced shear exfoliation method using graphite. The high hydrophobicity and surface area of Gr make it attractive as a solid-contact ion-to-electron transducer for potentiometric K+ sensors, in which the electrodes are fabricated through a screen-printing process. The electrochemical characterization demonstrates that Gr solid contact results in a high double-layer capacitance, potential stability, and strong resistance against water layer, gases, and light. The Gr-based K+ sensors showed a Nernstian slope of 53.53 mV/log[K+] within a linear concentration range of 10−1–10−4 M, a low detection limit of 10−4.28 M, a fast response time of ~8 s, good repeatability, and excellent long-term stability. Moreover, the Gr-based K+ sensors provided accurate ion concentrations in actual samples of human sweat and sports drinks.

The objective of the present study was to assess the suitability and efficiency of synthesized Polypyrrole-Antimony(III)iodophosphate (Ppy-SbIP) nanocomposite for the removal of Cd(II) from aqueous solution. Nanocomposite cation exchanger membrane was prepared by solution casting method using Polypyrrole-Antimony(III)iodophosphate and polyvinyl chloride (PVC) as a binder. The synthesis of membrane was confirmed by characterization of the nanocomposite membrane by various instrumentation techniques like SEM, EDX, FTIR, XRD, TGA. The experimental equilibrium data were tested by various potentiometric studies like Calibration curve, Transport no., Effect of pH, Response time, Potentiometric titration studies. The experimental data was best followed by selective for Cd(II) metal, having detection limit (1×10-9 M to 1×10-1 M), response time (20s) and working pH range (3-8). The analytical utility of this electrode was established by employing it as an indicator electrode in potentiometric titration. Various experimental parameter studies proved the absorption of Cd(II) on nanocomposite. Therefore, the present nanocomposite could be applied to purify metal contained wastewater

A new type of magnetically-separable nanocatalyst was prepared through the immobilization of phosphomolybdic acid (H3PMo12O40) in 10–30 wt.% on the surface of core-shell zirconia-coated magnetite nanoparticle (nano-Fe3O4@ZrO2). The developed heterogeneous nano-sized acid catalyst named nano-Fe3O4@ZrO2 supported PMA (or n-Fe3O4@ZrO2/PMA) was characterized using several techniques such as FT-IR, XRD, FE-SEM, VSM, EDX, TEM and TGA. The characterization data derived from FT-IR spectroscopy exhibited that H3PMo12O40 species on the support retained their Keggin structures. Additionally, the potentiometric titration with n-butylamine was employed to measure the acidity content of the as-obtained catalyst. Surprisingly, this novel active solid acid catalyst displayed to have a higher number of surface active sites compared to its homogeneous analogues. Besides, the catalytic activity of the catalyst was evaluated in multicomponent reactions (MRCs) for the rapid and efficient one-pot synthesis of 2, 4, 5-trisubstituted and 1, 2, 4, 5-tetrasubstituted imidazoles in high yields and selectivity. The sample of 20 wt.% displayed higher acidity content which led to its enhanced activity in the catalytic transformation. Moreover, the catalyst could be easily reused without deactivation after five runs, which made it a promising catalyst for practical and large-scale applications. This outstanding reusability was ascribed to the strong attachment of PMA molecules on the n-Fe3O4@ZrO2 support material. Keywords: Nano-Fe3O4@ZrO2 supported PMA, Core-shell zirconia-coated magnetite nanoparticles, Heterogeneous nanocatalyst, Reusability, Multicomponent reaction (MRCs)

Two methods for obtaining of benzoaza-15(18)-crown-5(6) ethers from 1,2-bis(2-iodoethoxy)benzene or diethyl 1,2-phenylenebis(oxy)diacetate have been reported. The ability of the crown ethers to coordinate lead(II) ions has been estimated by potentiometric and NMR methods.

New water soluble copper(II) complexes, - [Cu(phen)(gln)(H2O)]NO3·H2O (1) and [Cu(dmphen)(gln)(H2O)]ClO4 (2) - (phen: 1,10-phenanthroline, dmphen: 4,7-dimethyl-1,10-phenanthroline, gln: l -glutamine), have been synthesized and characterized by CHN analysis, ATR-FT-MIR, ESI-MS and single-crystal X-ray diffraction techniques. Binary and ternary complexes of copper(II) with the selected ligands have been investigated using potentiometric methods in 0.1 M KCl aqueous ionic media at 298.2 K. The protonation constants of the selected ligands and the stability constants of the complexes 1 and 2 have been calculated from the potentiometric data using the “BEST” software package and the potentiometric results have been analyzed using the “SPE” software package. The binding interaction of the complexes with calf thymus DNA (CT-DNA) was investigated by electronic absorption and emission spectroscopic methods revealed that the complexes could interact with CT-DNA via a moderate intercalation mode. The fluorescence quenching mechanism of bovine serum albumin (BSA) by the complexes was analyzed and the binding constant has been calculated. In vitro antiproliferative effect of the complexes was examined on human tumor cell lines (Caco-2, A549 and MCF-7) and healthy cells (BEAS-2B). The complex 2 showed remarkable antiproliferative activity compared to the complex 1 and cisplatin.

Potentiometric aptasensors enhanced by integrating advanced nanomaterials are of particular interest for the detection of multiplex species (e.g., proteins, bacteria, micro-organisms) due to their low cost, ease of operation, and low detection limits. However, potentiometric detection of small ionic species aptasensors is still challenging. This article describes the first example of a label-free G-quadruplex-based potentiometric aptasensing platform for the detection of Pb2+. Polyion oligonucleotide-labeled gold nanoparticles (AuNPs-DNA) as probes are modified on Au electrode, providing high-density negative charge on the electrode surface. These signal-amplifying probes can selectively form G-quadruplexes with the presence of Pb2+ ions and reduce the negative charges on the electrode surface, hence achieving potentiometric detection of Pb2+ ions with high selectivity. The AuNPs-DNA-based aptasensor shows an acceptable sensitivity over a wide range from 10−11 to 10−6 M with a detection limit of 8.5 pM. Furthermore, confirmed by coupled plasma mass spectrometry, the sensing platform is capable of performing effective and accurate detection of Pb2+ level in real water samples. The presented aptasensor offers a fast, convenient, low-maintenance, and highly sensitive alternative for on-site water pollution detections.

The discrepancy between concentrations and activities is a predicament well known to the analytical chemist. Because of the difficulty of determining activity coefficients, the standard technique for quantitative equilibrium studies is to work under a particular 'constant ionic strength' by adding an excess of an inert salt. Under such conditions, activity coefficients are approximately constant and can be taken into the equilibrium constants which are defined for the chosen ionic strength (I). Here we propose a fundamentally different approach. Throughout the numerical analysis of the titration data, activity coefficients for all individual species are approximated by well-known equations based on the work of Debye-Hückel. The computational analysis of the measurements strictly obeys the law of mass conservation and obeys the law of mass action only approximately. The main novelty is that now the addition of inert salts is no longer required and measurements are done at minimal I. Consequently, the thermodynamic equilibrium constants are now determined much more robustly based on experiments taken at low I. The approach has been tested and validated with the two very well investigated 3-protic phosphoric and citric acids. In summary: the technique of artificially keeping ionic strength constant has been replaced by improved computational analysis.

Water soluble hydrazide based O-carboxymethyl chitosan Schiff base ligands have been prepared from chitosan and a mixture of benzoic acidhydrazide with β-diketone by carboxymethylation using mono chloroaceticacid (MCA) through in-situ reaction. The degree of deacetylation of chitosan was determined by elemental analysis and potentiometric titration. Schiff base ligands and the functional groups were characterised by FT-IR, 1H, and 13C NMR spectroscopic techniques. The crystallinity of ligands and complexes was evaluated by X-ray powder diffraction (XRD) studies. Thermal stability of all the synthesized compounds was investigated by thermo gravimetric analysis and differential thermal analysis (TGA-DTA) which revealed the presence of metal oxide (CuO) residue to elevate the temperature to >500 °C. Filed emission scanning electron microscopic (FESEM) analysis revealed that Cu (II) complexes were more amorphous in nature than chitosan and Schiff base ligands. Vibrating sample magnetometer (VSM) studies reported that the d9 configuration of the metal complex was paramagnetic in nature and the geometry of the complex was square pyramidal. The antimicrobial activity of the synthesized hydrazide Cu (II) complexes was characterised by agar plate method, anti-inflammatory study was characterised by egg albumin denaturation technique and total antioxidant activity was characterised by phosphomolybdenum method.

Analytical techniques are extensively used in various fields of human activity to define quality and usage safety patterns of goods and consumables. Between those, liquid chromatography is probably the most common, generally combined with optical detectors. Alternatively, electroanalytical techniques provide versatile tools that offer high selectivity and sensitivity in a short time, using simple and low cost instrumentation. Amperometric, coulometric and conductimetric detectors are thus well established in HPLC with commercially available instrumentation. Despite sharing some of the stated features, the use of potentiometric detectors seems however overlooked. Potentiometry with ion-selective electrodes has been highlighted in both batch and flow analysis systems, evidenced by numerous applications performed worldwide. The determination of electrolytes in blood samples, heavy metals in natural water samples and pharmaceutical drugs in bulk drug materials are some of the representative examples. The developments achieved so far in hydrodynamic separation systems proved the great potential of potentiometry to become a competitive detection technique with the many others. Therefore, it is intended to present an overview about potentiometric detection in liquid chromatography with the purpose of enhance its importance for future analytical applications.

Tritium management is one of the main challenges that future nuclear fusion energy has to achieve. Accurate tritium monitoring is a basic task in order to have relying fusion reactors. High temperature sensors have to be developed to make this monitoring a reality. Hydrogen sensors based on solid-state electrolytes can be a reliable option to perform this monitoring. These types of sensors offer resistance to harsh chemical environments, temperature depending conductivity and quick and easy to measure signals. Potentiometric and amperometric hydrogen sensors based on solid-state electrolytes were previously studied in our research group. These previous sensors contained a pellet-shaped solid-state electrolyte. Using a one-end closed tube geometry the active area of the sensor increases. This new shape was obtained by a slip casting process. The satisfactory results obtained with both amperometric and potentiometric sensors present a promising path to the development of high temperature tritium sensors that could be used in the breeding blankets of the future nuclear fusion reactors. In the present work, amperometric sensors performance has been improved by increasing the electrolyte’s active area. Enlarging the electrolyte’s area gives the sensor more sensitivity and reduces its limit of detection and quantification. Analytical parameters of the sensor were compared to other electrochemical hydrogen sensors.

Metal complexes involving a chelation between copper(II) and the tripeptides, sarcosyl- l -leucyl-phenylalanine (Sar-Leu-Phe) and glycyl- l -leucyl-phenylalanine (Gly-Leu-Phe), have been identified as potential therapeutic drugs for rheumatoid arthritis. However, in solution the speciation and exact coordination of these tripeptides to copper(II) is unknown and as a result this was investigated using glass electrode potentiometry, ultraviolet–visible spectrophotometry, infrared spectroscopy and 1H NMR and CW EPR spectroscopies. The same basicity was found for the terminal amine of both tripeptides, but the methyl group on Sar decreased the copper(II) complex stability constants by 0.38–1.67 log units. Four species: ML, MLH-1, ML2H-1 and MLH-2 were found for both tripeptides in the pH range 2–11. The dissociated protons are from the amide groups. Room temperature and frozen solution EPR spectra support the existence of MLH-1, MLH-2 and ML2H-1 (a large excess was required for the ML2H-1 species). The two species, MLH-2 and ML2H-1, have a CuN3O equatorial chromophore, which therefore produce similar room temperature EPR spectra, with similar magnetic parameters. Frozen solution EPR spectra revealed different anisotropic magnetic parameters in axial symmetry, thus suggesting the presence of two different geometries. The lower g|| and the higher A|| values indicate that the geometry of the MLH-2 complexes tends more towards square planar, instead of the usual expected tetragonally elongated octahedral geometry. Copper(II) could coordinate to each tripeptide via an amine-N, two amide-Ns, two carbonyl-Os and a carboxyl-O. The proposed coordination modes were validated using quantum mechanical calculations.

TiO2 and Sn+4 doped TiO2 nanoparticles were prepared via the surfactant-assisted sol-gel method. Then, H3PW12O40 (PTA) was loaded over Sn-TiO2 nanoparticles with different PTA contents by wet impregnation method. The samples have been characterized by XRD, TEM, SEM, FTIR, UV–vis diffuse reflection (DRS) and photoluminescence spectroscopy (PL). The surface acidity was studied by potentiometric titration and the pyridine was used as probe molecules to distinguish between Bronsted and Lewis acid sites. XRD patterns analysis indicates that the crystallite size reduced remarkably with increasing PTA loading. TEM and SEM images exhibit irregular particles shape and the amount of PTA on the Sn-TiO2 surface increased with increasing PTA loading up to 60% wt. The addition of PTA and Sn+4 improved the surface acidity and catalytic activity of TiO2. Moreover, the addition of Sn+4 promoted the electrons transfer between PTA and TiO2 and reduced the recombination of electrons (e–) and holes (h+). The catalytic activity was tested by synthesis of 7-hydroxy-4-methyl coumarin and 14-phenyl-14H-dibenzo [a,j] xanthene. Both the acidity and catalytic activity increased sharply after modification Sn-TiO2 by PTA and the sample with 50 wt.% PTA showed the highest acidity and catalytic activity. Also, the photocatalytic performance of PTA/Sn-TiO2 was confirmed in the degradation of Methylene Blue (MB) and Rhodamine B (RhB) under UV–vis irradiations. The mineralization of MB and RhB were confirmed by Chemical oxygen demand (COD) and total organic carbon (TOC). The results indicate that 20% PTA/Sn-TiO2 showed the highest photocatalytic activity.

The detection of a drug belonging to the Sulfonamide class of compounds, namely Sulfapyridine, is reported in this work using an in-situ and fast potentiometric method. The strategy employed for this detection is based on the novel ion pair complex, [Sulfapyridine-H]+[Co(C2B9H11)2]- acting as the active site for highly selective recognition of Sulfapyridine. This enables the sensor's selectivity to be improved by incorporating the target molecule to the selective membrane. In this work, all solid state Sulfapyridine selective microelectrodes based on PVC-type membranes were prepared using three different plasticizers and the aforementioned ion pair complex. The sensors developed have provided quick and accurate response within the range of 10−6 mol/dm3 to 10−3 mol/dm3 of Sulfapyridine concentration and showed a Nernstian slope between 47 and 61 depending upon the type of plasticizer used. The lowest limit of detection achieved was 4 μmol/dm3. The potentiometric coefficient of selectivity, KA,Bpot, has shown that the Sulfapyridine-selective microsensors were highly selective towards Sulfapyridine even when compared to other members of the Sulfonamides class of compounds. In addition, from the Reilley diagram it can be observed that the sensor signal is stable for a working pH interval between 6.00 and 8.00.

Hypothesis The surface charging and adsorption properties of beryllium oxide follow the same principles as the properties of other metal oxides. Experiments The point of zero charge PZC was determined by potentiometric titration, and by salt addition method at 15, 25 and 35 °C. The ζ potential of beryllium oxide was measured at different concentrations of various 1-1 salts. The effect of ionic surfactants and of multivalent inorganic ions on the isoelectric point IEP was studied. Findings The PZC of beryllium oxide in the presence of NaCl is at pH 9.1 at 25 °C, and it decreases by 0.04 pH unit per 1 °C. The IEP of beryllium oxide in the presence of NaCl, KCl and KNO3 is at pH about 9, and it is independent of the electrolyte concentration and of aging. The presence of anionic surfactant (SDS) and of phosphate results in a shift in the IEP to low pH, and the presence of cationic surfactant (CTAB) results in a shift in the IEP to high pH. The IEP roughly matches the maximum in the particle size. The surface charging behavior of beryllium oxide confirms specific adsorption of ionic surfactants and of multivalent inorganic ions, and it is qualitatively similar to that of more common metal oxides (titania, alumina, hematite).

Metal-resistant bacteria can survive exposure to high metal concentrations without any negative impact on their growth. Biosorption is considered to be one of the more effective detoxification mechanisms acting in most bacteria. However, molecular-scale characterization of metal biosorption by wild metal-resistant bacteria has been limited. In this study, the Pb(II) biosorption behavior of Serratia Se1998 isolated from Pb-contaminated soil was investigated through macroscopic and microscopic techniques. A four discrete site non-electrostatic model fit the potentiometric titration data best, suggesting a distribution of phosphodiester, carboxyl, phosphoryl, and amino or hydroxyl groups on the cell surface. The presence of these functional groups was verified by the attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, which also indicated that carboxyl and phosphoryl sites participated in Pb(II) binding simultaneously. The negative enthalpy (−9.11 kJ mol−1) and large positive entropy (81.52 J mol−1 K−1) of Pb(II) binding with the bacteria suggested the formation of inner-sphere complexes by an exothermic process. X-ray absorption fine structure (XAFS) analysis further indicated monodentate inner-sphere binding of Pb(II) through formation of C−O−Pb and P−O−Pb bonds. We inferred that C−O−Pb bonds formed on the flagellar surfaces, establishing a self-protective barrier against exterior metal stressors. This study has important implications for an improved understanding of metal-resistance mechanisms in wild bacteria and provides guidance for the construction of genetically engineered bacteria for remediation purposes.

This work reports the unusual results on studying the operability and capability of a solid state electrochemical sensor based on a proton-conducting material to analyze the oxygen concentration in a gas media at elevated temperatures. This sensor consists of two ceramic parts made of CaZr0.9In0.1O3–δ, one of which acts as a hydrogen pump element, while another as a potentiometric detection element. A limiting current, occurring at a certain voltage value applied to the former element, is a sensor's response; it forms the concentration or temperature calibration curves, which can be used for the subsequent electrochemical analysis at high temperatures. The presented results expand the possibilities for utilizing the proton-conducting materials in new electrochemical (analytical) directions.

Nowadays, development of highly efficient potentiometric sensors attracts the attention of many researchers over the world; due to the great expansion of portable analytical devices. This study aims to apply a current development to the construction and sense of carbon paste sensors based on flowered-like Mg-Al layered double hydroxides/multiwalled carbon nanotubes (FLLDH/MWCNTs) (sensor І), FLLDH/titanate nanotubes (TNTs) (sensor ІІ) and MWCNTs/TNTs (sensor ІІІ) nanocomposites for bambuterol hydrochloride analysis; to enhance the potentiometric response towards determination of the drug. The sensors exhibited excellent Nernstian slopes 58.8 ± 0.5, 58.5 ± 0.8 and 57.4 ± 0.7 mV/decade with linear working ranges of 1.0 × 10−7–1.0 × 10−2, 1.0 × 10−6–1.0 × 10−2 and 1.0 × 10−7–1.0 × 10−2 mol L−1, detection limits 2.3 × 10−8, 2.5 × 10−7and 7.5 × 10−8 mol L−1 and quantification limits of 7.6 × 10−8, 8.3 × 10−7and 2.5 × 10−7 mol L−1 for sensor І, ІІ and ІІІ, respectively. The selectivity behaviour of the investigated sensors was tested against biologically important blood electrolytes (Na+, K+, Mg2+, Ca2+). The proposed analytical method was successfully applied for BAM determination in pure drug, pharmaceutical products, surface water, human plasma and urine samples with excellent recovery data (99.62, 99.10 and 98.95%) for the three sensors, respectively.