Nernstian Potentiometric Response Research Articles

Novel Green Screen-Printed Potentiometric Sensor for Monitoring Antihistamine Drug Chlorphenoxamine HCl in Various Matrices

The pharmaceutical sector is seeking cost-effective analyzers that deliver precise, real-time data. This study aims to establish a correlation between the pharmaceutical industry and advancements in solid-contact ion-selective electrodes for quantifying chlorphenoxamine hydrochloride (CPX) concentration in various matrices. A comparative analysis of the performance between solid contact and liquid contact sensors showed that solid contact sensors outperformed their liquid contact counterparts in terms of durability, handling, and ease of integration. A sensor was developed using MWCNT and calix[8]arene as ionophore, resulting in a Nernstian potentiometric response for CPX across a linear range of 5.0 × 10−5 to 1.0 × 10−8 M. The slope of the response was 57.89 ± 0.77 mV/decade, and the standard potential was determined to be 371.9 ± 0.8 mV. The developed sensor exhibits notable intrinsic advantages, such as a rapid response time of 12 ± 2 s and an extended lifespan of 3 months. The sensor exhibiting optimal performance has been effectively employed for the analysis of CPX in different matrices, including pharmaceutical formulations, urine, and plasma. The developed method underwent validation in compliance with ICH requirements. Finally, the method’s greenness and whiteness were evaluated using five different tools and successfully compared to those obtained from the established reported method.

A micro-fabricated potentiometric platform with application in a COVID-19 drug quantification and the determination of its binding affinity to a supramolecular host

Recent applications in host–guest chemistry include advanced sensing technologies, drug formulations, and drug delivery. Quantification of host–guest binding constants is significant to the continued optimization of their use. Binding constants offer valuable information about the stability and affinity of the formedcomplex that is essential to both drug formulations and delivery. In this study a novel green, portable, disposable, and cost-efficient microfabricated potentiometric sensor is introduced and successfully applied to determine the concentration of remdesivir (RMD), a COVID-19 drug, and its binding affinity to the supramolecular host sulfobutylether-β-cyclodextrin (SBEβCD) as a compatible solubilizing agent; to overcome the low water solubility of RMD which presents a significant challenge in its intravenous administration. The sensor incorporates multi-walled carbon nanotubes to improve stability and detection limits. To reduce interference effects and enhance the selectivity of the sensor for RMD, 4-tert-butyl-calix[8]arene was employed as an ionophore. A Nernstian potentiometric response for RMD over a concentration range of 1.0 × 10−3 to 1.0 × 10−6 M with a slope of 58.2 ± 0.9 mV decade−1 and a detection limit of 0.23 µM were achieved. The binding constant of the RMD-SBEβCD complex was determined to be 9.76 × 103 M−1. The proposed sensor was shown to be effective for drug quantification and measurements of binding affinities, providing valuable insights into the physicochemical properties of target drugs.

Nanoparticle-enhanced in-line potentiometric ion sensor for point-of-care diagnostics for tropicamide abuse in biological fluid

Point of care (POC), also identified as on-site testing, has evolved as a rapid and accurate technique for drug of abuse screening and analysis. The aim of this work is to detect tropicamide (TPC) abuse in biological fluids; we selected rat plasma as example. We developed a disposal miniaturized, portable, green, and budget-friendly POC solid-state electrochemical sensor based on potentiometric transduction. To attain that, an innovative microfabricated electrode modified with conducting polymer poly(3-octylthiophene) (POT) has been placed on sensitized printed circuit board (PCB). A two-stage optimization process was implemented to develop the fabricated electrode. The first stage of the optimization process depends on screening various ionophores in order to enhance the sensor selectivity towards tropicamide. Copper nanoparticles exhibited the highest selectivity towards TPC. The second stage was utilizing a polymer as an ion-to-electron transducer layer between the copper nanoparticles impregnated ion sensing membrane and the microfabricated solid-contact ion-selective electrode. This polymer was added to boost the stability of the potential drift (1.2 mV/h) due to the hydrophobic behavior of the POT, which precludes the formation of an aqueous layer at the Cu electrode/polymeric membrane interface and improve the limit of detection (1.1 × 10−8 M). Nernstian potentiometric response was accomplished for TPC with a slope of 58.46 ± 0.43 mV/decade and E0 ∼ 189.39 ± 2.12 over the concentration range 1.0 × 10−7 to 1.0 × 10−2 M. The suggested sensor's intrinsic figure of merits include a quick response time (13 ± 2 s) and long life time (45 days). The proposed sensor has been successfully employed in the selective determination of TPC in pharmaceutical formulations, and biological fluids. When the results were compared to those of the official approach, there was no statistically significant difference. The Eco-Scale tool assessed and measured the greenness profile of the established method.

A Reliable Electrochemical Sensor Based on Functionalized Magnetite Nanoparticles for Over‐the‐counter Allergy Medication Abuse Sensing in Biological Fluids

AbstractDiphenhydramine (DIPH) has become one of the world‘s most widely abused over‐the‐counter medications. In addition to relieving allergy symptoms, it is also recognized for causing elevated energy and mild euphoric effects. The U.S. Food and Drug Administration (FDA) has recently warned about serious problems at high doses including heart problems, seizures, coma or even death among addicted teenagers. Herein, a simple, cost‐effective, and reliable nanocomposite based electrochemical sensor was designed for DIPH quantification in biological fluids. Introducing the functionalized Fe3O4 nanoparticles (NPs) into the inner‐filling solution and the PVC‐based ion sensing membrane has been employed and compared to the classical potentiometric approach. The nanoparticles were incorporated to endorse in situ cooperative ion‐pairing interaction between the ionophore and DIPH, and to improve the selectivity and detection limit (9.5×10−8 M). Nernstian potentiometric response was achieved for DIPH over the concentration range of 1.0×10−7 to 1.0×10−2 M with a slope of 59.0±0.2 mV/decade. Inherent merits of the proposed sensor include fast response time (6 s), superior stability (60 days) with higher sensitivity and selectivity towards DIPH without interference from co‐formulated drugs and several ions commonly found in biological matrices. The proposed sensor was successfully applied to the potentiometric determination of DIPH in different biological fluids (plasma and human milk) with an average recovery of 99.06±1.95 % and 100.34±1.92 %, respectively. As a consequence, the developed ISE might be the ideal choice for in‐line DIPH measurements in plasma samples to identify overdose ingestion and its related symptoms, as well as for quality‐control laboratories without prior treatments.

The Origin of the Non-Constancy of the Bulk Resistance of Ion-Selective Electrode Membranes within the Nernstian Response Range.

The dependence of the bulk resistance of membranes of ionophore-based ion-selective electrodes (ISEs) on the composition of mixed electrolyte solutions, within the range of the Nernstian potentiometric response, is studied by chronopotentiometric and impedance measurements. In parallel to the resistance, water uptake by the membranes is also studied gravimetrically. The similarity of the respective curves is registered and explained in terms of heterogeneity of the membranes due to the presence of dispersed aqueous phase (water droplets). It is concluded that the electrochemical equilibrium is established between aqueous solution and the continuous organic phase, while the resistance refers to the membrane as whole, and water droplets hamper the charge transfer across the membranes. In this way, it is explained why the membrane bulk resistance is not constant within the range of the Nernstian potentiometric response of ISEs.

Point-of-care diagnostics for drugs of abuse in biological fluids: application of amicrofabricated disposable copper potentiometric sensor.

The major objective of this work was to develop a portable, disposable, cost-effective, and reliable POC solid-state electrochemical sensor based on potentiometric transduction to detect benzodiazepine abuse, mainly diazepam (DZP), in biological fluids. To achieve that, microfabricated Cu electrodes on aprinted circuit board modified with the conducting polymer poly(3-octylthiophene) (POT) have been employed as a substrate. This polymer was introduced to enhance the stability of the potential drift (0.9mV/h) and improve the limit of detection (0.126nmolmL-1). Nernstian potentiometric response was achieved for DZP over the concentration range 1.0 × 10-2 to 5.0 × 10-7molL-1 with a slope of 55.0 ± 0.4mV/decade and E0 ~ 478.9 ± 0.9. Intrinsic merits of the proposed sensor include rapid response time (11± 2s) and long life time (3months). In order to enhance the selectivity of the potentiometric sensor towards the target drug and minimize any false positive results, calix[4]arene (CX4) was impregnated as an ionophore within the PVC plastic ion-sensing membrane. The performance of the POC sensors was assessed using electrochemical methods of analysis and electrochemical impedance spectroscopy as a surface characterization tool. The studied sensors were applied tothe potentiometric determination of DZP in different biological fluids (plasma, urine, saliva, and human milk) in the presence of its metabolite with an average recovery of100.9± 1.3%, 99.4 ± 1.0%, 101.8 ± 1.2%, and 99.0 ± 2.0%, respectively. Graphical abstract.

Paradox of the Variation of the Bulk Resistance of Potassium Ion-Selective Electrode Membranes within Nernstian Potentiometric Response Range

Bulk resistance and other electrochemical properties of membranes of K+-selective electrodes (ISEs) containing valinomycin are measured by means of chronopotentiometry and electrochemical impedance. It is shown that the bulk resistance of the membranes, within the Nernstian potentiometric response range, increases along decrease of KCl concentration in solution. Analogous results were reported earlier for Ca2+ and NO$$_{3}^{ - }$$ ISEs. This non-constancy of the bulk resistance is in conflict with current views on the mechanism of ISEs response. Tentatively, this paradox is ascribed to heterogeneity of membranes due to water uptake from solution.

Electrochemical Properties of Nitrate-Selective Electrodes: The Dependence of Resistance on the Solution Concentration.

The electrochemical properties of ion-exchanger-based solvent polymeric ion-selective electrodes (ISEs)—bulk and interfacial resistance, capacitance, and polarization under a galvanostatic current step—are studied, with a nitrate ISE based on tetradecylammonium nitrate (TDANO3) as a model system. The study is performed by chronopotentiometric and impedance measurements, and focuses on the dependence of the aforementioned properties on the concentration of NO3− anions in solution. The impacts from the bulk and the interfacial charge transfer to the overall membrane resistance are revealed. It is shown that the bulk resistance of the membranes decreases over an increase of NO3− concentration within the range of a Nernstian potentiometric response of the ISE. This fact, also reported earlier for K+- and Ca2+-selective ISEs, is not in line with current views of the mechanism of the ISE response, or of the role of ion exchange in particular. The origin of this effect is unclear. Estimates are made for the concentration of ionized species (NO3− and TDA+) and, respectively, for the TDANO3 association constant, as well as for the species diffusion coefficients in the membrane.

A wide-range solid state potentiometric pH sensor based on poly-dopamine coated carbon nano-onion electrodes

A novel potentiometric pH sensor based on polydopamine films coated on a carbon nano-onion conductive surface is introduced. Glassy carbon electrodes containing a carbon nano-onion layer were modified by electropolymerization and self-polymerization of dopamine. The modified surfaces were characterized by ESEM, RAMAN spectroscopy and cyclic voltammetry. The modified electrodes displayed an almost Nernstian potentiometric response over the pH range 2–10. Furthermore, the pH sensors exhibit a fast and reversible behavior toward variations of pH and negligible interference effects from monovalent cations. The sensors showed an excellent correspondence between the pH values obtained using the GCE/CNO/PDA electrodes and those measured with glass electrodes and were applied to the analysis of real samples covering a wide pH range from 2.2 to 8.3. The analytical performance is comparable to other reported devices based on electropolymerized amines over graphite and noble metal electrodes. Their reproducible and stable response and their ease of fabrication is very promising for the miniaturization and integration of pH sensors in (bio)analytical devices.

Electrochemistry and Ion Sensing Properties of Conducting Hydrogel Layers Based on Polypyrrole and Alkoxysulfonated Poly(3,4‐ethylenedioxythiophene) (PEDOT‐S)

AbstractAcidic aqueous solutions containing pyrrole and alkoxysulfonated PEDOT derivative (PEDOT‐S) were found to undergo polymerization in the absence of an external oxidizing agent. The product was a nearly black‐colored conducting hydrogel that after separation could be dispersed in water or acetone. The suspensions could be used to deposit cast films on a polycrystalline gold electrode. The polymer modified electrode showed a nearly Nernstian potentiometric response to Ag+ cations in the concentration range of 10−5–10−1 M with the slope of 54 mV/decade. The response was specific to Ag+ compared to a series of alkali and transition‐metal cations (pKAg/M>3.7).

A highly sensitive PVC membrane iodide electrode based on complexes of mercury(II) as neutral carrier.

A novel solvent polymeric membrane electrode based on bis(1,3,4-thiadiazole) complexes of Hg(II) is described which has excellent selectivity and sensitivity toward iodide ion. The electrode, containing 1,4-bis(5-methyl-1,3,4-thiadiazole-2-yl-thio)butanemercury(II) [Hg(II)BMTB(NO3)4], has a Nernstian potentiometric response from 2.0 x 10(-8) to 2.0 x 10(-2) mol L(-1) with a detection limit of 8.0 x 10(-9) mol L(-1) and a slope of -59.0+/-0.5 mV/decade in 0.01 mol L(-1) phosphate buffer solution (pH 3.0, 20 degrees C). The selectivity sequence observed is iodide>bromide>thiocyanate>nitrite>nitrate>chloride>perchlorate>acetate>sulfate. The selectivity behavior is discussed in terms of the UV-Vis spectrum, and the process of transfer of iodide across the membrane interface is investigated by use of the AC impedance technique. The electrode was successfully applied to the determination of iodide in Jialing River and Spring in Jinyun Mountains, with satisfactory results.

Highly Selective PVC‐Based Membrane Electrode Based on 2,6‐Diphenylpyrylium Fluoroborate

AbstractA highly selective PVC‐membrane electrode based on 2,6‐diphenylpyrylium fluoroborate is presented. The electrode reveals a Nernstian potentiometric response for sulfate ion over a wide concentration range (5.0 × 10−6‐1.0 × 10−1 M). The electrode has a response time of about 10 s and can be used for at least 2 months without any divergence. The proposed sensor revealed very good selectivities for sulfate over a wide variety of common organic and inorganic anions and could be used over a wide pH range (2.5–9.5). The detection limit of the sensor is 3.0 × 10−6 M. It was successfully applied to the direct determination of salbutamol, paramomycin tablets, and as an indicator electrode for potentiometric titration of sulfate ions with barium ions.

Polymeric membrane electrodes with enhanced fluoride selectivity using Zr(IV)-porphyrins functioning as neutral carriers

Poly(vinyl chloride) polymeric membranes plasticized with o-NPOE ( o-nitrophenyl octyl ether) or DOS (dibutyl sebacate) and containing Zr(IV)-octaethyl(OEP)- or Zr(IV)-tetraphenylporphyrins (TPP) along with lipophilic cationic additives (tridodecylmethylammonium chloride; TDMACl) are examined potentiometrically and optically with respect to their response toward fluoride. It is shown that these zirconium porphyrins can function as neutral anion carriers within the organic membranes of the electrodes. Spectrophotometric measurements of thin polymeric films indicate that the presence of lipophilic cationic sites in the form of TDMA + and use of lower dielectric constant plasticizer (DOS) prevents formation of metalloporphyrin dimers in the organic polymer phase, which have been observed previously in polymeric membranes formulated with the same Zr(IV) porphyrins but with lipophilic anion site additives. By preventing dimer formation, rapid and Nernstian potentiometric response of the corresponding membrane electrodes toward fluoride ion is observed. Indeed, electrodes prepared with PVC/DOS membranes containing Zr(IV)-OEP and 15 mol% of TDMACl (relative to the ionophore) exhibit fast ( t 95<15 s) and reversible response toward fluoride. The slope of calibration plots are near-Nernstian (−59.9 mV per decade). Such electrodes display the following selectivity pattern: ClO 4 −>SCN −>F −>NO 3 −>Br −>Cl −, which differs significantly from the classical Hofmeister series, with greatly enhanced potentiometric selectivity toward fluoride. The data presented herein, coupled with results from a previous study, confirm that Zr(IV) porphyrins can serve as either charged or neutral type anion carriers with respect to their enhanced interactions with fluoride when used as ionophores to prepare liquid–polymeric membrane electrodes, and that the nature of membrane additives and plasticizer dictates the response mechanism at play for given membrane formulations.

A Novel PVC Membrane Sensor for Selective Determination of Cerium(III) Ions

A PVC membrane of azomethine of piperonylidine-4-[2.2]paracyclophanylamine reveals a Nernstian potentiometric response (with slope of 19.3 ± 0.3 mV/decade) for Ce(III) over a wide concentration range (10−1−2.5 × 10−5 mol L−1). The potential of this electrode is independent of pH in the range of 4.5–8.0. It has a fast response time of 30 s and can be used for a period of two months with good reproducibility. The detection limit of this membrane electrode is 1.2 × 10−5 mol L−1. The nature of the azomethine compound and its cerium(III) complex is examined using Fourier-transform infrared analysis, elemental analysis, and X-ray fluorescence techniques. This sensor exhibits a very good selectivities for Ce(III) over a wide variety of metal ions. The proposed sensor has been used as an indicator electrode in the potentiometric titration of carbonate and oxalate ions and in determination of acetyl salicylate content in some drugs.

Towards reversibility of ion transfer across the interface between valinomycin membranes and aqueous electrolyte solutions

Valinomycin-based potassium-selective membranes doped with potassium tetrakis(4-chlorophenyl)borate (KClTPB) or sodium tetrakis(4-fluorophenyl)borate (NaFTPB) are studied in KCl, NaCl, and CaCl2 solutions by potentiometric and electrochemical impedance methods. Before contact with KCl, membranes doped with NaFTPB provide Nernstian potentiometric response to Na+ ions, which is lost after conditioning the membranes in KCl. The membranes doped with KClTPB even before contact with KCl give no Nernstian response to Na+ ions. In CaCl2 solutions, none of the membranes provide a regular potentiometric response. Despite the difference in potentiometric behavior, the impedance spectra of the membranes are very similar in all solutions regardless of prior conditioning of the membranes. No evidence for a hindrance towards charge transfer processes is observed. The results suggest that the membrane/solution interface is reversible for interfering ions as well as for potassium, and the contamination of solutions with the latter is the sole reason for the lack of Nernstian response in the interfering electrolytes.

Polymeric membrane ion-selective electrode for determination of bismuth (III) in pharmaceutical substances

A PVC-based membrane of tridecylmethylammonium chloride reveals a Nernstian potentiometric response (with slope of 55 mV/decade and a correlation coefficient of 0.99) for complex of bismuth (III) with ethylenediaminetetraacetate-anion [Bi(EDTA)] − over a wide concentration range (1×10 −1 to 3×10 −5 mol/l). The potential of this electrode is independent of pH in the range of 4.0–11.0. It has a fast response time of about 30 s and was used for a period of 3 months with good reproducibility. The detection limit of this membrane electrode was 1×10 −5 M. This sensor exhibits a very good selectivity for [Bi(EDTA)] over a wide variety of complex metal ions with ethylenediaminetetraacetic acid. The proposed electrode has been used in the direct potentiometric monitoring of bismuth (III) in stomach anti-acids.

Cobalt(II)-selective membrane electrode based on a recently synthesized benzo-substituted macrocyclic diamide.

A PVC-membrane electrode based on a recently synthesized 18-membered macrocyclic diamide is presented. The electrode reveals a Nernstian potentiometric response for Co2+ over a wide concentration range (2.0 x 10(-6)-1.0 x 10(-2) M). The electrode has a response time of about 10 s and can be used for at least 2 months without any divergence. The proposed sensor revealed very good selectivities for Co2+ over a wide variety of other metal ions, and could be used over a wide pH range (3.0-8.0). The detection limit of the sensor is 6.0 x 10(-7) M. It was successfully applied to the direct determination and potentiometric titration of cobalt ion.

Threshold ionic site concentrations required for Nernstian potentiometric responses of neutral ionophore-incorporated ion-selective liquid membranes.

An equation that can describe the concentrations of ionic sites required for a Nernstian potentiometric response slope of neutral ionophore-incorporated ion-selective liquid membranes is presented. This equation is derived from a model based on electrical diffuse layers on both the membrane and the aqueous sides of the interface, in which the phase boundary potential is correlated to the surface charge density as well as the salt concentrations in the bulk membrane and aqueous solution. To experimentally and accurately confirm the validity of this equation, response characteristics of field effect transistors covered by neutral ionophore-based liquid membranes with varying concentrations of a derivative of tetraphenylborate as an anionic site but free of ionic impurities were examined. The observed membrane potentials and the response slopes for membranes with various concentrations of anionic sites were in good agreement with the values calculated from the theory presented in this paper with the measured complexation stability constants for the relevant systems. This result indicates that the theoretical prediction based on the proposed equation for the anionic site concentration is accessible for the preparation of neutral ionophore-incorporated ion-selective liquid membranes, which show Nernstian response slopes for the primary ions.

Highly selective electrode for Nickel (II) ion based on 1.5-diphenylthiocarbazone (dithizone)

PVC-based membrane of 1,5-diphenylthiocarbazone reveals a Nernstian potentiometric response with the slope of 29.5±1 mV per decade for Ni 2+ over a wide concentration range (5.0×10 −6 to 1.0×10 −2 mol/dm −3), the response time of the electrode is quite short and was used for a period of 2 months with a good reproducibility. The detection limit of this electrde was 2.8×10 −6 M. The proposed electrode revealed very high selectivity for Ni 2+ in the presence of a wide variety of metal ions such as Zn 2+, Pb 2+, Ag +, Cd 2+, Cu 2+, Co 2+, Ba 2+, Mg 2+, Tl +, Hg 2+ and Fe 2+ at concentrations<1×10 −3 M.

Chromium(III) ion-selective electrode based on 4-dimethylaminoazobenzene

A PVC-based membrane of 4-dimethylaminoazobenzene reveals a Nernstian potentiometric response (with slope of 19.5±0.6 mV/decade and a correlation coefficient of 0.999) for Cr(III) over a wide concentration range (1.66× 10 −6–1.0×10 −2 mol dm −3). The potential of this electrode is independent of pH in the range of 3.0–5.5. It has a fast response time of about 10 s and was used for a period of 3 months with good reproducibility. The detection limits of this membrane electrode was 8×10 −7 M. the proposed electrode has been used as an indicator electrode in the potentiometric titration of Cr(III) with EDTA. This sensor exhibits a very good selectivities for Cr(III) over a wide variety of metal ions.