Direct Potentiometric Measurement Research Articles

Sertraline: Theoretical Studies and a New Potentiometric PVC Membrane Sensor for its Determination

Background: Sertraline (ST) hydrochloride is an anti-depressant of the selective serotonin reuptake inhibitor (SSRI) class. Potentiometric sensors are an appealing route for detecting drugs due to some advantages in terms of sensitivity, feasibility, selectivity, fast response, tolerance to turbidity and colour of solutions, and cost-effectiveness. Methods: A mixture of polyvinyl chloride powder (PVC) with o-nitrophenyl octyl ether and the ion association complex was dissolved in tetrahydrofuran (THF) to prepare the membrane for the proposed sensor. The sensor was calibrated and then electrochemically used for detecting ST in pharmaceutical samples. Results: The near Nernstian response was observed for a concentration of 1.0 x 10-8 – 1.0 x 10-2 mol L-1 with 58.62 mV as a slope per concentration decade. This direct potentiometric measurement resulted in average recoveries of 96.0 ± 0.2%. Moreover, good selectivity for sertraline with respect to many inorganic and organic cations was observed. Conclusion: The proposed sensor was simple to use and produced accurate and precise results. The molecule's chemical and biological activities were revealed using theoretical calculations. Regarding the chemical activities, calculations were made on the 3-21g and 6-31g while the SDD bases were set at B3LYP, HF, and the M062X level. Molecular docking calculations were designed against cancer proteins in order to have details regarding the molecule's biological activity.

Research Progress of the Ion Activity Coefficient of Polyelectrolytes: A Review.

Polyelectrolyte has wide applications in biomedicine, agriculture and soft robotics. However, it is among one of the least understood physical systems because of the complex interplay of electrostatics and polymer nature. In this review, a comprehensive description is presented on experimental and theoretical studies of the activity coefficient, one of the most important thermodynamic properties of polyelectrolyte. Experimental methods to measure the activity coefficient were introduced, including direct potentiometric measurement and indirect methods such as isopiestic measurement and solubility measurement. Next, progress on the various theoretical approaches was presented, ranging from analytical, empirical and simulation methods. Finally, challenges for future development are proposed on this field.

Synthesis of a Functionalized Carbon Nanotube Graphene Composite Enabling pH-Responsive Electrochemical Sensing for Biomedical Applications

Sensing of pH value plays an important role in many fields of studies including biology, chemistry, and biomedicine. In recent years, nanomaterials have emerged as a promising sensing element for a variety of applications. In this study, we report a high-sensitivity pH sensor synthesized by a functionalized single-wall carbon nanotube graphene (FSWCNT/G) composite. This sensor was constructed with Cr/Au electrodes and FSWCNT/G sealed in a PDMS microchannel on a glass substrate. The experiments of a field-effect transistor (FET), linear sweep voltammetry (LSV), and response time measurement all proved the superiority of the fabricated composite sensor over a pristine graphene sensor. A high potentiometric gradient of 98.75 mV/pH within the operating pH range of 4–10 was obtained in direct potentiometric measurements. The composite nanosensor can be used to monitor the pH value in cancer cell solution. Moreover, the composite nanosensor was tested for cancer cell detection, and the range of the concentration detection was from 5 × 106 to 2.5 × 105 cells/mL, showing a potential way to achieve label-free cell detection.

A New, MWCNT-Based, Solid-State Thiabendazole-Selective Sensor

Direct potentiometric measurements using solid-state sensors have a great potential for thiabendazole (TBZ) determination, considering simplicity, accuracy, and low cost. Modifying the sensing material of the sensor with multi-walled carbon nanotubes (MWCNTs) leads to improved analytical properties of the sensor. In this study, a new potentiometric solid-state sensor for TBZ determination, based on MWCNTs modified with a sulfate group, and TBZ ion as sensing material was developed. The sensor exhibited a Nernstian response for TBZ (60.4 mV/decade of activity) in a working range between 8.6 × 10−7 and 1.0 × 10−3 M. The detection limit for TBZ was 6.2 × 10−7 M. The response time of the sensor for TBZ was 8 s, and its signal drift was only 1.7 mV/h. The new sensor is applicable for direct potentiometric determination of TBZ in complex real samples, such as fruit peel. The accuracy of TBZ determination is confirmed using the standard addition method.

Ionic strength-independent potentiometric cation concentration sensing on paper using a tetrabutylammonium-based reference electrode

Ion-selective electrodes (ISEs) are known not to strictly measure the concentration of ions, but their activities. The relationship between the two varies with ionic strength, which may result in measurement errors if samples of variable ionic strength are measured and concentration is chosen as the sensor output. Traditionally, concentration readings from potentiometric signals have been possible if the ionic strength of the solution matches that of the calibrant or is made constant by an ionic strength adjusting buffer. In this work, a direct concentration output is realized for a potassium-selective electrode by using a TBA+ (tetrabutylammonium)-selective membrane as the reference electrode and preloading a TBA+ salt in the solution channel. It is shown that the activity coefficients for K+ and TBA+ change similarly to effectively cancel out the influence of ionic strength, allowing for direct potentiometric concentration measurements with deviations from ideality of < 1 mV. The approach was realized on paper-based analytical devices (PADs). The potentiometric concentration data on paper were found to be independent of ionic strength and, owing to their geometric feature, of sample volume. K+ concentration in grape juice, infused water and green tea analyzed by the newly developed PADs showed good correspondence with Atomic Emission Spectroscopy (AES).

Hydrosulfide-selective ChemFETs for aqueous H2S/HS− measurement

We have prepared and characterized hydrosulfide-selective ChemFET devices based on a nitrile butadiene rubber membrane containing tetraoctylammonium nitrate as a chemical recognition element that is applied to commercially available field-effect transistors. The sensors have fast (120 s) reversible responses, selectivity over other biologically relevant thiol-containing species, detection limits of 8 mM, and a detection range from approximately 5 to 500 mM. Sensitivities are shown to be 53 mV per decade at pH 8. Use of this compact, benchtop sensor platform requires little training – only the ability to measure DC voltage, which can be accomplished with a conventional multimeter or a simple analog data acquisition device paired with a personal computer. To the best of our knowledge, this report describes the first example of direct potentiometric measurement of the hydrosulfide ion in water.

PH analysis and dental erosive potential of bottled water commercialized in Portugal

Introduction: The knowledge of drinks' pH is essential for the development of preventive strategies in patients at risk of dental erosion [1], since this defines the erosive potential of a drink. The critical pH, below which demineralization is expected to occur is 5.2–5.5 in enamel [2]. Bottled water is often considered innocuous for dental tissues, both by patients and clinicians, and the erosive potential of different brands is neglected, especially in patients with dry mouth symptoms who need a strong water reinforcement [3]. The aim of this study is to demonstrate that bottled waters, commercialized in Portugal, have a minimum erosive potential for enamel, based on the measurement of their pH. Materials and methods: 31 different bottled mineral water, commercialized in Portugal, were analysed by means of the hydrogenionic concentration, by direct potentiometric measurement using a pH electrode calibrated in the range 4.01-10.00. Five independent pH measurements were recorded at 25 °C immediately after opening each bottle, for later calculation of the mean value and standard deviation. Results: From the 31 analysed bottled mineral water, three have shown a mean pH value within or very close to the critical pH range for demineralization (namely bottled waters Dia, Salutis and Vitalis), while the remaining 28 have shown to have mean pH values above. None of the measured waters had a pH mean value below 5.2 (Table 1). Discussion and conclusions: With the results of this preliminary study, we can demonstrate that bottled mineral waters commercialized in Portugal have minimal erosive potential on human dental enamel, based on the pH mean value. Nevertheless, it is essential for the clinician to be aware of the erosive potential of bottled water and educate patients as a preventive strategy. A further investigation concerning this area is needed for wider conclusions.

Graded interference with the direct potentiometric measurement of sodium by hemoglobin

ObjectivesSodium concentration is measured by either indirect (INa) or direct potentiometry (DNa), on chemistry and gas panels, respectively. A spurious difference between these methods (ΔNa=INa−DNa) can be confusing to the clinician. For example, variation in serum total protein (TP) is well known to selectively interfere with INa. Red cells have been suggested to interfere with DNa, but both positive and negative interference have been reported. In this study, the effect of gas panel hemoglobin (Hb) on ΔNa was examined. MethodsΔNa was calculated in 772 pairs of closely-timed chemistry and gas panels (median: 4min. apart), retrospectively collected from our critical care units, with 1 pair per patient. Hb was treated as a categorical or continuous variable and tested for linear and non-linear effects, with adjustment for 3 known influences on ΔNa—TP, bicarbonate (tCO2), and the chemistry-gas panel glucose difference (ΔGlu). ResultsHb ranged from 3.5 to 22.0g/dL [35–220g/L]. In categorical analysis, ΔNa increased with Hb, and the effect was essentially linear. By simple regression, ΔNa rose 0.06±0.03[SE]mmol/L per 1g/dL [10g/L] increase in Hb (p<0.05), but confounding was suspected because Hb also correlated (p<10−3) with TP, tCO2, and ΔGlu. Using multiple regression to adjust for the confounders, ΔNa rose 0.15±0.03mmol/L per 1g/dL [10g/L] rise in Hb (p<10−6). ConclusionsIncreasing Hb spuriously decreases DNa and increases ΔNa. A linear correction for this artifact can reduce the discordance between INa and DNa, promoting their interchangeable use.

Fabrication of a new nanocomposite modified carbon paste Al3+-ion selective electrode based on N,N′-dipyridoxyl (1,2-cyclohexanediamine) (PYCA) as an active material

Construction and feature of a nanocomposite modified carbon paste electrode for aluminum(III) ion determination based on N,N′-dipyridoxyl (1,2-cyclohexanediamine) (PYCA) as a novel selector material will be covered by this paper. The optimum composition, Nernstian slope/linear range/detection limit in the forms of calibration graph, response time, utilizable pH range, repeatability and precision of measurements of the aluminum(III) ion using the new fabricated Al3+-CPE was evaluated. The optimal composition which performed over Al+3 ion concentration range 1.0 × 10−8 mol L−1–1.0 × 10−1 mol L−1 with near-Nernstian slope equal 20.9 ± 0.2 mV decade−1 and low detection limit about 5.0 × 10−9 mol L−1, was formed of ionophore (PYCA 3 %), binder (paraffin oil 30 %), modifier [multi-wall carbon nanotubes (MWCNTs) 1 %] & [Nanosilica (NS) 0.5 %], and inert matrix (graphite powder 65.5). The request time to give rise Nernstian response of electrode for concentrations from 1.0 × 10−8 mol L−1 to 1.0 × 10−1 mol L−1 of Al3+ ion solution was estimated about ~6 s. The new Al3+-CPE was applied in pH range 2.0–5.0 with no consequential change in potential response. To verify the selectivity of electrode toward aluminum(III) ion in the presence of different metallic cations, matched potential method was used. The obtain results in analytical applications reflect the excellent ability of this electrode to play the role as endpoint indicator electrode in both titration and direct potentiometric measurements.

24 Direct potentiometric measurement for chloride ion using Spotchem Arkray analyser adapted to sweat samples

Objectives: Sweat testing following pilocarpin iontophoresis is the preferred method to check for cystic fibrosis. Correct measurement and interpretation of results are essential components of cystic fibrosis testing. Methods: All sweat tests performed in the years 2005 to 2010 in our cystic fibrosis centre were analyzed retrospectively. Pilocarpin iontophoresis was in accordance to established international guidelines. All samples were analyzed using chloridometry (Chloridmeter, Kreienbaum, Germany) and conductivity measurement (SweatCheck, WesCor Inc., USA). Results were interpreted as negative, indeterminate or positive according to international guidelines (chloridometry) or manufacturer’s recommendation (conductivity measurement). Results: 1246 sweat tests were performed on 1077 patients. 68 patients were 18 years or older. Median age at testing was 1.58 years (min. 14 days, max. 77 years). Comparison of conductivity measurement and chloridometry reveals a constantly higher NaCl equivalent in conductivity measurement (mean value of difference 24.1±10.7mmol/l). In 91.4% the assessment of test results reveals consistent diagnoses. 0.9% of patients would not have received a second test if only conductivity measurement had been used although chloridometry revealed positive or indeterminate results. Discussion: Sweat testing remains a particularly paediatric topic. The gold standard is chloridometry. This study underlines the inappropriate comparability of conductivity measurement and chloridometry with consequently higher values in conductivity measurement. Special reference values allow a consistent interpretation in many cases but not in all.

Direct potentiometric determination of diastase activity in honey

A novel method for the determination of diastase activity is reported. The method is based on a direct potentiometric measurement of triiodide ion that is released when a starch–triiodide complex is hydrolysed by honey diastase. The increase of free triiodide ion concentration in a sample is found to be directly proportional to the diastase activity of the sample.A response mechanism of the platinum redox electrode is proposed, allowing a calculation of the diastase activity factor (F). The sensor and analyte parameters, including F, were obtained by least squares fitting of potentiometric data using the optimisation function of the Solver add-in of Microsoft Excel. The values of F obtained by the new direct potentiometric method were compared with those obtained using the standard Phadebas method (DN values), and the two values were found to agree within experimental error. Finally, the diastase activity of nine varieties of honey was determined using the novel method developed here.

Determination of the botanical origin of starch using direct potentiometry and PCA

Abstract A new approach for the determination of the botanical origin of starch is presented based on the formation of starch–triiodide complexes. The starch samples were extracted from wheat (Srpanjka), potato, maize, rye (Barun), barley (Conduct), rice, tapioca and a commercial modified starch. The amylose/amylopectin ratios of starches, among various other properties, differ between starches of different botanical origins. Triiodide ions bind characteristically to the amylose and amylopectin of the starch depending on the starch's origin. The new technique includes direct potentiometric measurements of the response of free triiodide ions in starch–triiodide solutions where the data is analysed by principal component analysis (PCA). PCA gave graphical results for statistical differentiation between starches of different botanical origins.

Discrimination of apple juice and herbal liqueur brands with solid-state electrodes covered with polyaniline and thiacalixarenes

Solid-contact ion-selective electrodes based on glassy carbon electrode covered with electropolymerized polyaniline and tetrasubstituted thiacalix[4]arene ionophores with hexyl and o-pyridylamido functional groups at the lower rim have been developed and examined in the discrimination of the brands of apple juices and herbal liqueurs. For this purpose, the liquids tested were diluted and spiked with a constant amount of Fe 3+ ions. The variation of the signal toward Fe 3+ ions was achieved due to their involvement in the reactions with the organic ligands and the antioxidants present. As was shown, the combination of the three electrodes with various receptors makes it possible to predict the brand of apple juices and herbal liqueurs using linear discriminant analysis in 95–100% cases. The discrimination procedure makes it possible to discriminate liquids within 20 min. Besides, the electrodes developed make it possible to detect individual antioxidants (ascorbic, malic, oxalic acids, hydroquinone, and quercetin) in the range from 5.0 × 10 −6 to 1.0 × 10 −2 M in direct potentiometric measurements and redox titration.

Development and Characterization of a New PVC-Membrane Electrode for Selective Sensing of K+ Ion

This paper describes a potassium ion-selective electrode based on 2,2-dithiodibenzoic acid with a focus on the sub-Nernstian response characteristics. The topics including the experimental parameters that influence the response of the electrode, useful membrane compositions and applications were investigated. The membrane electrode demonstrate linear (R2= 0.999) sub-Nernstian responses, with the slop of 40.12 ± 0.15 mV/decade, toward potassium(I) ions over the range of 1.0 x 10– 5 to 1.0 M. The prepared electrode, with detection limit of 6.2 x 10-6 M, was successfully applied in the direct potentiometric measurement of sub-milimolar quantities of K+ in aqueous solutions. The results were compared with atomic absorption spectrometry measurements. There was good agreement between the results from the proposed electrode and those from the standard method.

수경재배용 배양액의 이온성분 분석을 위한 고체형 센서 모듈 개발

A solid state ion sensor module has been developed and evaluated for hydroponic nutrients analysis. The sensor module consisted of five ion-selective electrodes (ISE) fabricated by screen-printing technology. The electrochemical responses of ion sensors for nitrate, ammonium, potassium, calcium, and pH were measured with specially designed 7-channel low voltage signal transducers. The analytical characteristics of the sensors were comparable with those of conventional ISE sensors. The solid state ion sensors exhibit linear relationships over five concentration decades. Detection limit of the sensors were depends on ions. Performance test results showed that relative errors of measured ion concentrations were less than 5% for ion, and pH. The concentration of , and pH ion in standard solution and nutrient solutions could be determined by direct potentiometric measurements without any conditioning before measurements.

Novel thiocyanate-selective membrane sensor based on crown ether-cetyltrimethyl ammonium thiocyanate ion-pair as a suitable ionophore

A potentiometric thiocyanate-selective sensor based on the use of crown ether-cetyltrimethyl ammonium-thiocyanate (CCT) as a neutral carrier for a thiocyanate-selective electrode is reported. The electrode was prepared by coating the membrane solution containing PVC, plasticizer, and carrier on the surface of graphite electrode. Influences of the membrane composition, pH, and possible interfering anions were investigated on the response properties of the electrode. The sensor exhibits significantly enhanced response toward thiocyanate ions over the concentration range 1 × 10 −6 to 1.0 × 10 −1 M with a lower detection limit of 0.03 μg ml −1 and a slope of −57.6 mV decade −1. Fast and stable response, good reproducibility, long-term stability, applicability over a wide pH range (3.8–9.2) are demonstrated. The sensor has a response time of ≤20 s and can be used for at least 6 weeks without any considerable divergence in their potential response. The proposed electrode shows fairly good discrimination of thiocyanate from several inorganic and organic anions. The sensor is used for direct potentiometric measurements of thiocyanate ions over the concentration range 0.06–5800 μg ml −1 and for monitoring sequential titration of some metal ions (e.g. Ag +, Cu +, Pb 2+) in binary and ternary mixtures. Sequential binding of these metal ions with SCN − ensures sharp stepwise titration curves with consecutive end point breaks at the equivalent points.

Calcium Pulstrodes with 10-Fold Enhanced Sensitivity for Measurements in the Physiological Concentration Range

Ion-selective electrodes ideally operate on the basis of the Nernst equation, which predicts less than 60- and 30-mV potential change for a 10-fold activity change of monovalent and divalent ions measured at room temperature, respectively. Typical concentration ranges in extracellular fluids are quite narrow for the electrolytes of key importance. A range of 2.2-2.6 mM for calcium ions, for instance, translates into just a 2.2-mV potential change. The direct potentiometric measurement of physiological electrolytes is certainly possible with direct potentiometry and is done routinely in clinical analyzers and handheld measuring devices. It places, however, strong demands on the precision of the reference electrode and requires careful temperature control and frequent calibration runs. In this paper, a robust 10-20-fold sensitivity enhancement for calcium measurements is attained by departing from the classical response mechanism and operating in a non-Nernstian response mode. Stable and reproducible super-Nernstian responses of these so-called pulstrodes in a narrow calcium activity range can be controlled by instrumental means in good agreement with theory. The potentials may be measured during a galvanostatic excitation pulse (mode I) or immediately after it (mode II), under open-circuit conditions. Subtraction of the potentials, sampled at different times during a single pulse, allows one to obtain a sensitive differential peak-shaped signal at a critical and fully adjustable analyte activity range. Calcium pulstrodes based on the diamide ionophore AU-1 were characterized and applied to the measurement in model physiological liquids. Super-Nernstian responses exceeding 700 mV/decade were observed in a physiological range of calcium concentration. Such remarkable sensitivity of the pulstrodes, complemented with the well-documented high selectivity of these potentiometric sensors, may provide a significant increase in the accuracy and precision of electrolyte measurements in clinical analysis.

Interactions between gelatin and sodium dodecyl sulphate: binding isotherm and solution properties

The interaction between sodium dodecyl sulphate (SDS) and gelatin was studied at pH 4.5 and 6.5 where the gelatin is positively charged (i.e.p. 8). At pH 4.5 a SDS/gelatin concentration range was found where gelatin precipitates. At pH 6.5 the SDS-gelatin complex remains soluble although three SDS concentration domains were distinguished where the SDS-gelatin complex had very different affinities for the solvent. Below C1 the complex was highly surface active but other measurements (viscosity, potentiometry, protons uptake) did not reveal any particular consequence of binding. Between C1 and C2 the molecular size decreased (viscosity lowering) upon charge neutralization and collapse about small SDS aggregates (17 SDS molecules per gelatin molecule). Above C2 a cooperative binding mechanism lead to the formation of SDS aggregates; the complex stretched out and turned strongly hydrophilic (the viscosity increases, low surface activity). At saturation one gelatin molecule bound about 200 SDS molecules. Above the overlap concentration (about 3 wt%) SDS aggregates formed between several gelatin molecules, the viscosity increased continuously with SDS concentration and the binding ratio was lower than in dilute gelatin solutions. A very good correspondence was found between the different analytical data including turbidity, viscosity, surface tension, protons uptake and direct potentiometric SDS binding measurements.

Numeric Simulation of Ion‐Site Association Effects in Ion‐Selective Electrode Response

AbstractEffects in ion‐selective electrode response and selectivity, caused by ion‐site association in membranes are studied by means of numeric simulations based on a generalized model, which does not rely on a certain degree of the dissociation of electrolytes in membranes. The variability of the experimental values of the potentiometric selectivity coefficients is considered in view of the association in membranes. The reasons why the “dissociation approach” often fits experimental data are also discussed. A novel version of segmented sandwich membrane method is proposed for direct potentiometric measurements of ion‐site association constants in membranes, and preliminary experimental results are presented.

양액의 영양분 분석을 위한 Strip형 이온선택성전극 센서 의 응용 -NO3이온 분석 -

A simple disposable thick-film potentiometric strip has been developed and evaluated for hydroponics application. The strip consisted of low ion-selective electrodes (ISE) fabricated by screen-printing technology. The electrochemical responses of ion sensors for nitrate, ammonium, potassium, and magnesium were measured with specially designed 16-channel low voltage signal transducers. The analytical characteristics of the sensors were comparable with those of conventional ISE sensors. The thick-film sensors exhibit linear relationships over five concentration decades. The concentration of N <TEX>$O_3$</TEX> - ion in standard solution can be determined by direct potentiometric measurements without any conditioning before measurements. However, measurement of <TEX>$K^{+}$</TEX>, N <TEX>$H_4$</TEX><TEX>$^{+}$</TEX>, and <TEX>$Mg^{2+}$</TEX> ionic concentrations in nutrient solutions seems not feasible.