Potentiometric Detection Research Articles

Paper-based microfluidic sampling for potentiometric determination of ions

In this work, paper-based microfluidic sampling was used together with potentiometric determination of ions (Cd2+, Cl−, Pb2+) and pH. Calibration solutions and samples were absorbed into paper substrates and potentiometric detection was performed by placing solid-state ion-selective electrodes (ISEs) and a reference electrode in direct contact with the paper substrate. The paper substrate was found to influence the determination of Pb2+ at low concentrations, indicating complexation of Pb2+ by chemically active groups present in paper. Paper-based microfluidic sampling was successfully applied in measurements of pH in various foodstuffs and environmental samples by employing a conventional pH glass electrode. However, some influence of the paper substrate on the measured pH was observed for samples with pH close to neutral. Despite some limitations, paper-based microfluidic sampling with potentiometric sensing opens new possibilities for direct chemical analysis of specific sample types. The method described in this work is particularly interesting for analysis of small sample volumes with a high content of solid impurities and for analysis of e.g. liquid or moisture from polluted surfaces and foodstuff.

FLOW INJECTION POTENTIOMETRIC ANALYSIS OF ASPARTIC ACID, GLUTAMIC ACID AND ASCORBIC ACID USING PLATINUM ELECTRODES

The presence of weak acids in solution can be detected using a potentiometric detector. Platinum was used as a working electrode and Ag/AgCl as a reference electrode. Ascorbic, glutamic and aspartic acid were detected by a platinum electrode in a flow potentiometric system. The influence of pH, flow rate and concentration of phosphate buffers asa a carrier were studied and showed an optimum pH for the detection of ascorbic and glutamic acid at pH 6,5 and pH 7,0 for aspartic acid. Phosphate buffer concentration optimum at 1x10-4M and flow rate of 1,00 mL/min. Linear range for ascorbic and glutamic acid at 2,5 x10-4M to 5x10-2M, with a regression coefficient of 0,974 and 0,958, while for aspartic acid 5x10-4M to 5x10-2M with a regression coefficient 0,911. Detection limit for ascorbic and glutamic acids were 5x10-4M and 1x10-3M for aspartic acid. Sensor reproducibility obtained from variation coefficient (Kv). Variation coeffiecient (Kv) of ascorbic acids 1,32-1,69%, glutamic acids 0,69- 1,57% and aspartic acid 0,54- 1,29%.

Precise determination of hypochlorite in commercial bleaches with established traceability using automatic potentiometric titration

A measurement procedure is proposed for precisely determining hypochlorite in commercial bleaches, with established traceability and a full description of its uncertainty sources. The procedure is based on automatic volumetric titration with potentiometric detection and was evaluated in the analysis of several commercial bleach samples, with Na-hypochlorite mass fractions in the range 0.002–0.027 g g−1, with an average expanded uncertainty (k = 2) of 0.00027 g g−1 and an average relative standard deviation between measurement triplicates of 0.36 %. Compared with a standard procedure based on manual volumetric titration with visual colorimetric detection, the improved procedure produced equivalent results with a lower average expanded uncertainty (0.00029 g g−1 as compared to 0.0015 g g−1 for the standard procedure). This was related to better precision of the volume measurement using an automatic buret and to better precision of the titration endpoint determination using potentiometric detection. Compared with other studies reported in the literature, the improved procedure presented a lower average relative standard deviation between measurement replicates (0.36 % as compared to 1.00–11.53 %).

A potentiometric immunosensor based on a ZnO field-effect transistor

The characteristics of an aptamer-modified Ta2O5/ZnO field-effect transistor as a prototype label-free immunosensor for the potentiometric electrical detection of immunoglobulin G (IgG) were studied. The Ta2O5/ZnO film was grown on a glass substrate by a facing-target sputtering method. Stable operation in electrolyte solution with a small hysteresis width and a low gate leakage current was realized. The immunosensor exhibited a proportional sensitivity to the logarithmic human IgG concentration in the range of 0.35–23 µmol·dm−3 with a rapid response time of ∼15 s.

A Novel Potentiometric Detection Strategy for the Determination of Amlodipine Besylate Based on Functionalized Particles

AbstractA novel potentiometric strategy based on functionalized magnetite nanoparticles and microparticles were compared with the classical potentiometric strategy. This strategy provided nano‐ and microsized particles that were highly dispersed and coated with ionophore and plasticizer to promote an in situ cooperative ion‐pairing interaction between the ionophore and the analyte present in inner solution of sensor membrane, compared to the classical technique. Three amlodipine (AML) sensors were constructed using functionalized nanoparticles in sensor 1; microparticles in sensor 2, as ionophores, and the polymeric membrane ionophoric property in sensor 3.

Effects of chemical treatment of indium tin oxide electrode on its surface roughness and work function

In this paper, we report the effects of chemical treatment of indium tin oxide (ITO) surface on its surface chemistry such as chemical composition and surface roughness and on its usage as an electrode with monolayer modification. Atomic force microscopy, angel-resolved X-ray photoelectron spectroscopy, and Kelvin probe force microscopy have been used to investigate the morphology and the chemical properties of commercial thin ITO films after several treatments commonly used prior to the formation of organic layer on the surface. The amount of spike present on the surface of as-received ITO substrates was significantly reduced by etching with KOH whereas the roughness of ITO increased with HCl etching. We demonstrated that the successive treatment of ITO electrode with HCl and KOH affects the surface characteristics such as roughness and work function, contributing to the potentiometric detection of tryptophan.

Potentiometric Detection of Saccharides Based on Highly Ordered Poly(aniline boronic acid) Nanotubes

Potentiometric detection of saccharides based on highly ordered poly(aniline boronic acid) (PABA) nanotubes modified electrode was systematically investigated. The PABA nanotubes were first fabricated by electrochemical polymerization of 3-Aminophenylboronic acid in an anodic alumina oxide (AAO) membrane. Their morphologies and structure were then characterized using scanning electron microscopy and FT-IR spectroscopy. The as-synthesized PABA nanotubes had a very porous structure with small diameters and high surface area. The sensitivity and response time of PABA nanotubes modified electrode to saccharides were discussed. The sensitivity of the sensor in connection with length of PABA nanotubes and pH of the solution was studied. The sensor showed much high sensitivity to D-glucose (ca. 1.5mVmM−1) and D-fructose (ca. 3.5mVmM−1) with fast response time for D-glucose (65s) and D-fructose (23s).

Standard addition flow method for potentiometric measurements at low concentration levels: Application to the determination of fluoride in food samples

A standard addition method was implemented by using a flow manifold able to perform automatically multiple standard additions and in-line sample treatment. This analytical strategy was based on the in-line mixing of sample and standard addition solutions, using a merging zone approach. The flow system aimed to exploit the standard addition method to quantify the target analyte particularly in cases where the analyte concentration in the matrix is below the lower limit of linear response of the detector. The feasibility of the proposed flow configuration was assessed through the potentiometric determination of fluoride in sea salts of different origins and different types of coffee infusions. The limit of quantification of the proposed manifold was 5×10−6molL−1, 10-fold lower than the lower limit of linear response of the potentiometric detector used. A determination rate of 8samplesh−1 was achieved considering an experimental procedure based on three standard additions per sample. The main advantage of the proposed strategy is the simple approach to perform multiple standard additions, which can be implemented with other ion selective electrodes, especially in cases when the primary ion is below the lower limit of linear response of the detector.

Qualitative analysis of the presence of emerging contaminants in water supplies for human use: a case study of the Guilherme de Azevedo reservoir in Caruaru (PE, Brazil)

Interest in studies related to emerging contaminants has increased among the scientific community. Although this area has only recently begun to be investigated, a number of important reports have been published, in which these substances have been shown to cause significant abnormalities in the endocrine system of animals, thereby directly affecting the environment and natural cycles. These emerging contaminants are generally pharmaceutical products that are used for personal hygiene, natural hormones, illicit drugs, industrial by-products and indicators of anthropogenic activity. The methodology adopted involved filtering samples with glass fibre and cellulose acetate membrane filters, extraction and concentration using the solid phase extraction (SPE) method, and analysis using potentiometric detectors incorporated in a continuous flow system. The identification of these contaminants in water supplies for human use is essential, although it is only the first and primordial phase in the development of future studies to discuss removal options.

Characterization of Carboxylated-SWCNT Based Potentiometric DNA Sensors by Electrochemical Technique and Comparison with Potentiometric Performance

Aptasensors for detection of thrombin were produced by covalently linking aptamer (ssDNA) to cSWCNT. Those biosensors were fully characterized by cyclic voltammetry to evaluate the electrode surface charge/ligand density. We performed the CV studies of electrostatically bound [Ru(NH3)6]3+ redox markers on aptamer surfaces and calculated aptamer surface charge density from the CV data. Potentiometric detection of thrombin allows then the correlation with the CV results. The electrode surfaces containing higher amount of aptamers exhibited better performance in potentiometric measurements. These investigations will introduce the pathway to build reusable and regenarable aptasensors including a simple, accurate and precise estimation of aptemer surface charge density to characterize the surface and hence to ensure the quality of apatsensors.

Thermodynamic analysis of free cyanide determination by silver nitrate titration in copper bearing solutions

The present study is a thermodynamic approach to explain the titration of free cyanide by silver nitrate in cyanide solutions containing copper. When copper is present in cyanide solutions, the visual determination of the endpoint of the titration leads to an overestimation of the free cyanide concentration that can be up to 56% when the indicator is potassium iodide, or up to 121% for rhodanine. Four alternatives were evaluated to detect the endpoint of the titration: visual detection with potassium iodide, visual detection with rhodanine, potentiometric endpoint detection with silver electrode and derivative curve of the potentiometric titration. The last two methods showed the best results (the smallest overestimation, reaching no more than 8%). A comparison between the titration graphs and the equilibrium composition diagrams allows the understanding of the overestimation, and permits the qualitative and quantitative determination of all the copper cyanide species that are being titrated with silver nitrate.Cette étude est une approche thermodynamique ayant pour but d’expliquer le titrage au nitrate d’argent du cyanure libre de solutions de cyanure contenant du cuivre. Lorsque le cuivre est présent dans les solutions de cyanure, la détermination visuelle du point final du titrage mène à une surestimation de la concentration du cyanure libre, qui peut aller jusqu’à 56% lorsque l’indicateur est l’iodure de potassium, ou jusqu’à 121% pour la rhodanine. On a évalué quatre solutions possibles de détection du point final du titrage: détection visuelle avec l’iodure de potassium, détection visuelle avec la rhodanine, détection potentiométrique du point final avec électrode d’argent et courbe dérivée du titrage potentiométrique. Les deux dernières méthodes ont montré les meilleurs résultats (surestimation la plus petite, n’atteignant pas plus de 8%). Une comparaison entre les graphes de titrage et les diagrammes d’équilibre de la composition permet de comprendre la surestimation et permet la détermination qualitative et quantitative de toutes les espèces du cyanure de cuivre qui sont titrées avec le nitrate d’argent.

Application of polyaniline for potentiometric recognition of salicylate and its analogues

Presented work proofs usability of polyaniline (PANI) as a receptor for potentiometric detection of salicylates. The potentiometric selectivity of PANI-coated membranes based on tridodecylmethylammonium chloride (TDDMACl) towards salicylate is at least as good as the selectivity of membranes based on “conventional” specific supramolecular receptor systems such as Sn(IV) and Al(III) phthalocyanates. X-ray diffraction (XRD) and electric impedance spectroscopy (EIS) techniques are used to insight into the phenomena leading to improvement of salicylate-selectivity of PANI. These studies reveal the relative role of sodium chloride during the PANI polymerization that leads to preparing of partially crystalline polymer and decreasing of the “bulk” resistance of membrane. The “bulk” resistance change is attributed to introduction of the electronic conductivity into the system PANI/Salicylate. Determination of acetylsalicylate in pharmaceutical preparations with recovery at about 98–100% is reported. Additionally, the ability to detect (0.11± 0.01)×10−3M of salicylate present in a synthetic serum sample is demonstrated.

A combination of dynamic measurement protocol and advanced data treatment to resolve the mixtures of chemically similar analytes with potentiometric multisensor system

Data processing techniques and measuring protocol are very important parts of the multisensor systems methodology. Complex analytical tasks like resolving the mixtures of two components with very similar chemical properties require special attention. We report on the application of non-linear (artificial neural networks, ANNs) and linear (projections on latent structures, PLS) regression techniques to the data obtained from the flow cell with potentiometric multisensor detection of neighouring lanthanides in the Periodic System of the elements (samarium, europium and gadolinium). Quantification of individual components in mixtures is possible with reasonable precision if dynamic components of the response are incorporated thanks to the use of an automated sequential injection analysis system. The average absolute error in prediction of lanthanides with PLS was around 1 × 10(-4)mol/L, while the use of ANNs allows the lowering of prediction errors down to 2 × 10(-5)mol/L in certain cases. The suggested protocol seems to be useful for other analytical applications where simultaneous determination of chemically similar analytes in mixtures is required.

Competitive-type displacement reaction for direct potentiometric detection of low-abundance protein

Prostate-specific antigen (PSA), one of the indications of possible prostate malignancy, is used as a biomarker for the diagnosis and prognosis of prostate cancer. Herein, we develop a new homogeneous potentiometric immunoassay for sensitive detection of low-concentration PSA without the need of sample separation and washing step. Two nanostructures including positively charged polyethyleneimine-poly(styrene-co-acrylic acid) (PEI-PSAA) nanospheres and negatively charged gold nanoparticles conjugated with anti-PSA antibody (Ab-AuNP) were first synthesized by using mulsifier-free emulsion copolymerization and wet chemistry method, respectively. Thereafter, the as-prepared PEI-PSAA was used as a pseudo hapten for the construction of immunosensing probe based on an electrostatic interaction between PEI-PSAA and Ab-AuNP. Upon target introduction, the added PSA competed with PEI-PASS for Ab-AuNP based on a specific antigen–antibody interaction, and displaced Ab-AuNP from PEI-PASS. The dissociated PEI-PASS was captured through the negatively charged Nafion- modified electrode, thereby resulting in the change of membrane potential. The fabrication process was characterized by using high-resolution transmission electron microscope (HRTEM), scanning electron microscope with energy-dispersive X-ray spectroscopy (SEM-EDX), surface plasmon resonance (SPR) and dynamic laser scattering (DLS) technique. Under optimal conditions, the output signal was indirectly proportional to the concentration of target PSA in the sample and exhibited a dynamic range from 0.1 to 50ng/mL with a detection limit (LOD) of 0.04ng/mL. Intra- and inter-assay coefficients of variation (CVs) were 6.8 and 7.5%, respectively. In addition, the methodology was evaluated for analysis of 12 clinical serum samples and showed good accordance between the results obtained by the developed immunosensing protocol and a commercialized enzyme-linked immunosorbent assay (ELISA) method.

Oxazinoindolines as Fluorescent H+ Turn-On Chromoionophores For Optical and Electrochemical Ion Sensors

We propose here a new class of fluorescent H(+) turn-on oxazinoindoline (Ox) dyes as chromoionophores suitable for the development of polymeric ion-selective membranes. Through rational design, oxazinoindolines with varying basicities and tunable absorption bands that extend to the near-infrared region were prepared. The basicities of the compounds were evaluated by potentiometry and fluorescence spectroscopy. By comparing the potentiometric lower detection limit with chromoionophore I (pKa = 14.80 ± 0.03 in PVC-NPOE), pKa values were determined for Ox Y, Ox R, and Ox B to be 9.80 ± 0.03, 12.85 ± 0.03, and 12.95 ± 0.03, respectively. Unlike conventional pH indicators that involve only a protonated and deprotonated form, a third species, arising from the thermal isomerization of the Ox compounds in polar solvents, may influence the overall protonation equilibrium. Interestingly, this results in an apparent pKa increase in the fluorescence mode when more polar PVC-NPOE membranes were utilized. The isomerization is suppressed in nonpolar PVC-DOS membranes. Na(+)-selective optical sensors were successfully prepared using the Ox dyes as an early application of the compounds in ion-selective optical sensors. The compounds were also successfully evaluated in a dynamic electrochemistry (chronopotentiometry) sensing mode for the detection of total alkalinity.

Fluorous Membrane Ion-Selective Electrodes for Perfluorinated Surfactants: Trace-Level Detection and in Situ Monitoring of Adsorption

Ion-selective electrodes (ISEs) with fluorous anion-exchanger membranes for the potentiometric detection of perfluorooctanoate (PFO(-)) and perfluorooctanesulfonate (PFOS(-)) were developed. Use of an anion-exchanger membrane doped with the tetraalkylphosphonium derivative (Rf8(CH2)2)(Rf6(CH2)2)3P(+) and an optimized measurement protocol resulted in detection limits of 2.3 × 10(-9) M (1.0 ppb) for PFO(-) and 8.6 × 10(-10) M (0.43 ppb) for PFOS(-). With their higher selectivity for PFO(-) over OH(-), membranes containing the alternative anion exchanger (Rf6(CH2)3)3PN(+)P((CH2)3Rf6)3 with a bis(phosphoranylidene)ammonium group further improved the detection limit for PFO(-) to 1.7 × 10(-10) M (0.070 ppb). These values are comparable with results obtained using well-established techniques such as gas chromatography-mass spectrometry (GC-MS), liquid chromatography-mass spectrometry (LC-MS), and liquid chromatography-tandem mass spectrometry (LC-MS-MS), but the measurement with ISEs avoids lengthy sample preconcentration, can be performed in situ, and is less costly. Even when eventual spectrometric confirmation of analyte identity is required, prescreening of large numbers of samples or in situ monitoring with ISEs may be of substantial benefit. To demonstrate a real-life application of these electrodes, in situ measurements were performed of the adsorption of PFOS(-) onto Ottawa sand, which is a standard sample often used in environmental sciences. The results obtained are consistent with those from an earlier LC-MS study, validating the usefulness of these sensors for environmental studies. Moreover, PFOS(-) was successfully measured in a background of water from Carnegie Lake.

Potentiometric detection and removal of copper using porphyrins

BackgroundCopper is an essential trace element with a great importance in industry, environment and biological systems. The great advantage of ion-selective sensors in comparison with other proposed techniques is that they are measuring the free metal ion activity which is responsible for their toxicity. Porphyrins are known to be among the best ionophores in formulation of ion-selective sensors.ResultsA symmetrically substituted meso-porphyrin, namely: 5,10,15,20-tetrakis(4-allyloxyphenyl)porphyrin (TAPP) was used in the construction of a new copper selective-sensor and was also tested for the removal of copper from waste waters. The potentiometric response characteristics (slope and selectivity) of copper-selective electrodes based on TAPP in o-nitrophenyloctylether (o-NPOE), dioctyl phtalate (DOP) and dioctyl sebacate (DOS) plasticized with poly(vinyl chloride) membranes are compared.ConclusionsThe best results were obtained for the membrane plasticized with DOP. The sensor has linear response in the range 1x10-7 – 1x10-1 M with 28.4 ± 0.4 mV/decade near-Nernstian slope towards copper ions and presents good selectivity. Due to its chelating nature, the same porphyrin was also tested for the retention of copper from synthetic copper samples, showing a maximum adsorption capacity of 280 mg/g.

Analysis of Potential Applicability of the Potentiometric Urea Biosensor to Real Samples

Since the production and use of chemical products are performing a marked growth, the charge, for fast and efficient mechanisms of environmental pollution control and monitoring, has increased. This charge has been made even more present in the rural scenario, especially with regard to fertilizers and nitrogen compounds, which have a high pollution potential. Several methods are used to urea determination, but usually they require a pretreatment or they are unsuitable for monitoring in situ. For this reason, urea biosensor can be a fast and cost-effective analytical technique to be used in extensive monitoring programs. Urea enzyme sensors based on potentiometric detection of ammonium ion, ammonia gas and carbon dioxide have been reported. In this study, the potential applicability of the potentiometric urea biosensor to real samples has been studied. The biocomponent used was jack beans, Canavalia ensiformis, a vegetal tissue rich in urease. The vegetal tissue was immobilized on nylon net by glutaraldehyde in order to improve the enzyme stability and the lifetime of the urea biosensor. Moreover, an ammonium ion-selective electrode was been chosen as the transducer. The instrument was applied to commercial urea fertilizer solutions and an environmental sample, the sugar-cane vinasse. The linear concentration range calibration curve was 1–20 ppm urea with a response time of 15 min. Urea biosensor could be reused for 70 days and the response was more than 95 % reproducible. Moreover, the urea biosensor was tested in real samples with qualitative promising responses.

Preparation of Cu (II) imprinted polymer electrode and its application for potentiometric and voltammetric determination of Cu (II)

The Cu (II) imprinted polymer glassy carbon electrode (GCE/Cu-IP) was prepared by electropolymerization of pyrrole at GCE in the presence of methyl red as a dopant and then imprinting by Cu2+ ions. This electrode was applied for potentiometric and voltammetric detection of Cu2+ ion. The potentiometric response of the electrode was linear within the Cu2+ concentration range of 3.9 × 10−6 to 5.0 × 10−2 M with a near-Nernstian slope of 29.0 mV decade−1 and a detection limit of 5.0 × 10−7 M. The electrode was also used for preconcentration anodic stripping voltammetry and results exhibited that peak currents for the incorporated copper species were dependent on the metal ion concentration in the range of 1.0 × 10−8 to 1.0 × 10−3 M and detection limit was 6.5 × 10−9 M. Also the selectivity of the prepared electrode was investigated. The imprinted polymer electrode was used for the successful assay of copper in two standard reference material samples.

Development of vapor generation combined with potentiometric detection for determination of sulfite in beverages

This paper describes a simple, sensitive and cost effective method developed for determination of sulfite in beverages. The procedure is based on chemical vapor generation of hydrogen sulfide, collection of the vapor in an alkaline solution, and then potentiometric determination of the sulfide using a commercial sulfide selective electrode. The influential parameters on analytical performance such as concentration of reagents, flow rate of carrier gas, reaction temperature and gas collection time are evaluated and discussed. In the optimum conditions, the method was linear in the range of 2–25 μg mL−1 of sulfite with a detection limit of 0.7 μg mL−1. The relative standard deviation of the method was 1.2 % for five replicate experiments at 10 μg mL−1 concentration level. The method was successfully applied for determination of sulfite in different beverages with the relative recoveries between 92.2 and 96.2 %. The proposed method can be applied for quality control and consumer safety in food and beverages industrial plants.