Separate Solution Method Research Articles

Carbon paste based sensor for sensitive Cr(III) ion determination in different water samples and anti-diabetic supplement

A modified carbon paste sensor based on N,N′-(((ethane-1,2-diylbis(oxy))bis(2,1-phenylene))bis(methanylylidene))bis(pyridine-2-amine; BPA Schiff base as Cr(III) selective carrier was fabricated and studied in this work. The proposed sensor homogenization and mechanism of action was studied by infra-red (IR) and scanning electron microscope (SEM) with energy dispersive X-ray (EDX) tools. The sensor covered 1.0 × 10−7–1.0 × 10–1 mol L−1 linear range and a detection limit of 7.22 × 10–8 mol L−1 for Cr(III) with 20.17 ± 0.13 mV decade−1 Nernstian slope. 5 s was the response time of the prepared sensor and it was reproducible and stable for 3 months. The working pH range was 3.3–6.0 and it also works well to determine Cr(III) ion in presence of water miscible solvents up to 12.5% content of the methanol and 17.5% of ethanol. The electrode’s selectivity was studied using separate and mixed solution methods for selectivity coefficients determination and the sensor showed good selectivity relative to a variety of metal ions (selectivity coefficients = 1.01 × 10−5–8.57 × 10−3). In addition, the practical analysis value of the sensor was demonstrated by measurement of Cr(III) quantitatively in mineral water, supplement and also as an indicator electrode in Cr(III) against EDTA potentiometric titration with good reproducibility (RSDs of 0.91–2.15%).

Highly selective and sensitive potentiometric determination of favipiravir in COVID-19 antiviral drug formulations

In this study, a novel all-solid-state electrochemical sensor based on favipiravir-tetraphenylborate (FAV-TPB) electroactive material was developed and reported for FAV’s highly selective and sensitive potentiometric determination in COVID-19 antiviral drug formulations. All-solid-state FAV selective sensor was fabricated by mixing and properly pressing FAV-TPB, graphite (G), multi-walled carbon nanotube (MWCNT), and paraffin oil (PO). In order to obtain the best sensor response, the sensor component ratios were optimized. The most satisfying response characteristics was obtained with the sensor composition FAV-TPB:G:MWCNT:PO in the ratio 32.5:42.5:5:20 (w/w %). The developed sensor displayed a wide linear near-Nernstian response to FAV over the concentration of 1.0 × 10−6 − 1.0 × 10−1 molL−1 with a slope of 53.6 ± 1.4 mV (R2 = 0.9997). The detection limits of the sensor was calculated as 6.0 × 10−7 molL−1, respectively. The dynamic response time of the sensor was 7 s, and the sensor exhibited fairly reproducible potentiometric responses. In the pH range of 6.0–8.0, the sensor’s potential response was not affected by the pH change of the test solutions. The improved sensor had a wide temperature tolerance, and its response remained unchanged in the 10–40 ℃ temperature range. The interference effect of some chemical and biological species was evaluated by the matched potential method and separate solution method. The sensor worked stable for 12 weeks without any considerable change in its potential response. The analytical applications of the sensor were successfully carried out with the potentiometric titration of FAV with sodium tetraphenylborate solution and also the direct determination of favipiravir in COVID-19 antiviral drug formulations.

Cheap and effective potentiometric PVC sensor for the determination of imidazolium based ionic liquids in aqueous and aqua-organic media

Owing to the extensive research on imidazolium based ionic liquids; the present study aims to design a potentiometric sensor for alkyl methylimidazolium ion. For this, poly(vinyl chloride) PVC membrane based on the neutral ion-pair complexes of cetylpyridinium chloride and sodium dodecyl sulfate (CPy+DS−) has been developed. The synthesized ion selective electrode (ISEs) have been found to show linear response with near-Nernstian slope for CnMeImCl (C10MeImCl, C12MeImCl and C14MeImCl). The proposed ISEs show quick response (5–6 s) and provide wide pH range for working. The influence of various ions on the performance of ion-selective electrode is investigated in terms of potentiometric selectivity coefficients, which were determined by separate solution method. The performance of synthesized ISE in examining the critical micellar concentration (cmc) of CnMeImCl in aqueous, aqua-organic media and in the presence of amino acids (glycine, L-glutamic acid and L-phenylalanine) has been found to be satisfactory and confirmed through conductivity and fluorescence measurements. This emphasizes its worth for in-situ analysis of alkyl methylimidazolium ions, during an organic reaction, and hence possible reaction mechanism evaluation. Different thermodynamic parameters such as Standard Gibbs energies of micellization (ΔGm∘), degree of counterion dissociation (α), amphiphile tail transfer Gibbs free energy (ΔGm,trans∘) have been evaluated. Further, the analytical application of synthesized electrode as end point indicator in the potentiometric titration of C14MeImCl with SDS has also been explored, which compared well with improved two-phase titration method. The current study is novel as it involves the use of a cheaper material (CPyCl) as ionophore and that the same electrode can be used for different chain alkyl methylimidazolium ions simply by changing the internal reference solutions.

Potentiometric Monitoring of Iodide Ions Using a Highly Selective Iodide Sensor Based on AgI-Cu2S-Multi Walled Carbon Nano Tube Material

In this work, a new iodide selective sensor based on an AgI-Cu2S-Multiwalled carbonnanotube-Graphite-Paraffin oil composite material was described for highly selective potentiometric determination of iodide ions. To obtain the best potentiometric performance characteristics of the sensor, the sensor components was optimized and the sensor was formed by properly pressing of the optimized sensor components. The experimental results were showed that the most appropriate potentiometric response was achieved with the sensor materials containing a compositions of G:MWCNT:AgI:Cu2S:PO in the ratio 50:5:20:5:20 (% w/w). The developed sensor display a wide linear working range (1.0×10-5-1.0×10-1 molL-1) for iodide ions. In this linear working range, the Nernstian slope of the sensor was 51.5±1.0 mV and the correlation coefficient (R2) was determined as 0.9991. The sensor was of a very low response time (5s). The repeatability of the sensor potential response was very good and its response remained unchanged in the pH range of 6.0-9.0. The interference effect on the sensor response of different anionic species was tested by the separate solution method (SSM) and the sensor selectivity was quite good. The life time of the sensor was measured as 13 weeks and the sensor was successfully used as indicator sensor for the potentiometric titrations of iodide ions with silver nitrate solution. Additionally, the sensor was successfully applied for the direct detection of iodide ions in environmental water samples.

Paper-Based Analytical Device Based on Potentiometric Transduction for Sensitive Determination of Phenobarbital.

In medicine, barbiturates are a class of depressive medications used as hypnotics, anticonvulsants, and anxiolytics. For the treatment of specific forms of epilepsy and seizures in young children in underdeveloped countries, the World Health Organization recommends phenobarbital (PBAR), a barbiturate drug. This review describes the fabrication and characterization of a paper-based analytical apparatus for phenobarbital detection that is straightforward, affordable, portable, and disposable. All of the solid-state ion-selective electrodes (ISEs) for PBAR as well as a Ag/AgCl reference electrode were constructed and optimized on a nonconductive paper substrate. Using carbon nanotube ink, the sensors were made to function as an ion-to-electron transducer and to make the paper conductive. A suitable polymeric membrane is drop-cast onto the surface of the carbon ink orifice. The pyrido-tetrapeptide and pyrido-hexapeptide derivatives, which were recently synthesized, functioned as distinct ionophores in the PBAR-membrane sensor, enabling its detection. With a detection limit of 5.0 × 10-7 M, the manufactured analytical device demonstrated a Nernstian response to PBAR anions in 50 mM phosphate buffer, pH 8.5, over a linear range of 1.0 × 10-6 to 1.0 × 10-3 M. The PBAR-based sensors showed quick (less than 5 s) response times for PBAR ion detection. The modified separate solution method was utilized to evaluate the selectivity pattern of these novel ionophores with respect to PBAR ions in comparison to other common anions. The analytical instrument that was exhibited on paper had good precision both within and between days. The suggested technology assisted in the detection of trace amounts of PBAR in real pharmaceutical samples. A comparison was made between the data acquired using the HPLC reference method and the information obtained by the recommended potentiometric approach. The described paper-based analytical device may be a good choice for point-of-care PBAR determination because it is cheap and easy to find and can self-pump (especially when combined with potentiometric detection).

Synthesis and surface characterization of a chemically modified carbon paste electrode and its application in determination of Hg(II) ion in water, food and dental amalgam samples

The development of an easy and affordable method for its determination in various samples is of major interest because the globe is affected by the toxicity of the environment caused by the presence of heavy metals, particularly mercuric ions. For the potentiometric measurement of Hg(II) ions in various materials, an unique carbon paste electrode was created using 1,3-Bis[2-(N-morpholino)acetamidothiophenoxy]propane (BMATPP) as a modifier. With a reaction time of six seconds, the electrode had a Nernstian slope of 30.01 ± 0.52 mV decade-1 over the concentration range of 5 × 10-9-1 × 10-3 mol/L (SD of 5 replicates). It was discovered that the pH range for use was 2.2 to 4.5 and that it was thermally stable up to 60 °C. The selectivity of the suggested sensor towards the Hg(II) ion was investigated using the separate solution method (SSM) and fixed interference technique (FIM), and it demonstrated a satisfactory selectivity. The interaction between the target Hg(II) ions and modifier was demonstrated by scanning electron microscopy (SEM) in conjunction with energy dispersive X-ray (EDX) and infrared (IR). The modifier's contact angle value demonstrated its lipophilicity, which is consistent with its stability and long life. With excellent F-test and t-test values obtained, the Hg(II) ion modified sensor was successfully used for potentiometric analysis of several real samples.

New Potentiometric Screen-Printed Platforms Modified with Reduced Graphene Oxide and Based on Man-Made Imprinted Receptors for Caffeine Assessment.

Caffeine is a psychoactive drug that is administered as a class II psychotropic substance. It is also considered a component of analgesics and cold medicines. Excessive intake of caffeine may lead to severe health damage or drug addiction problems. The assessment of normal caffeine consumption from abusive use is not conclusive, and the cut-off value for biological samples has not been established. Herein, new cost-effective and robust all-solid-state platforms based on potentiometric transduction were fabricated and successfully utilized for caffeine assessment. The platforms were modified with reduced graphene oxide (rGO). Tailored caffeine-imprinted polymeric beads (MIPs) based on methacrylic acid (MAA) and ethylene glycol dimethacrylate (EGDMA) were prepared, characterized, and used as recognition receptors in the presented potentiometric sensing devices. In 50 mM MES buffer, the sensors exhibited a slope response of 51.2 ± 0.9 mV/decade (n = 6, R2 = 0.997) over the linear range of 4.5 × 10−6–1.0 × 10−3 M with a detection limit of 3.0 × 10−6 M. They exhibited fast detection of caffeinium ions with less than 5 s response time (<5 s). The behavior of the presented sensors towards caffeinium ions over many common organic and inorganic cations was evaluated using the modified separate solution method (MSSM). Inter-day and intra-day precision for the presented analytical device was also evaluated. Successful applications of the presented caffeine sensors for caffeine determination in commercial tea and coffee and different pharmaceutical formulations were carried out. The data obtained were compared with those obtained by the standard liquid chromatographic approach. The presented analytical device can be considered an attractive tool for caffeine determination because of its affordability and vast availability, particularly when combined with potentiometric detection.

Ultrasonic aided synthesis of a novel mesoporous cobalt-based metal-organic framework and its application in Cr(III) ion determination in centrum multivitamin and real water samples

A novel Co-based metal organic framework (Co-MOF) was applied as an electroactive material in carbon paste electrode for determination of Cr(III) ion with high selectivity and sensitivity. This Co-MOF was established by transforming the monoclinic structure of the Schiff base as a linker into a 3-D Co-MOF tetragonal system using the cobalt ion as a node under a 1.5:1 M ratio between the Schiff base and cobalt ion by using sonochemical synthesis under optimal conditions. Many characteristic tools were used to test the newly synthesized Co-MOF. The Co-MOF would have a nanometric, mesoporous character (average particle size 45–73 nm and pore diameter 5.0467 nm), 270.201 m2g−1 surface area, and hydrophobicity (average contact angle = 143.23°). Because of its large surface area, porous structure, and electrocatalytic behavior, metal organic framework is a fascinating material to use as an ionophore. This newly synthesized Co-MOF ionophore has been used to determine Cr(III) ions in a variety of samples with high accuracy and precision (RSD % = 0.75–2.55) and the data illustrated a concord with those acquired by atomic absorption spectroscopy (AAS). The proposed carbon paste electrode showed a Nernstian slope of 19.96 ± 0.53 mV decade-1 with a detection limit of 4.3 × 10-9 mol L-1, covering a linear range of 5.0 × 10-9 – 1.0 × 10-2 mol L-1 and fast response time of (<10 s) with long-time stability of 2 months over pH range of 3.0 – 6.2. The proposed sensor was highly selective for Cr(III) ions, and the values of selectivity coefficients assessed using the fixed interference method (FIM) and the separate solution method (SSM) which were long recognized.

PVC membrane, coated-wire, and carbon-paste electrodes for potentiometric determination of vardenafil hydrochloride in tablet formulations and urine samples

Comparative study was made between three designs of vardenafil ion (Vr)-selective electrodes: a poly vinyl chloride (PVC) membrane (liquid inner contact) called electrode A, copper-coated (solid contact) called electrode B and a modified carbon paste electrode (CPE) called electrode C based on vardenafil - tetraphenylborate (Vr-TPB) as ion-exchanger complex. Electrode A has a linear dynamic range from 4.5X10-6 – 1.0X10-2 ​M, with a Nernstian slope of 51.8 mV/ decade and a detection limit of 1.6X10-6 ​M. Electrode B shows linearity over the concentration range from 8.0X10-6 - 1.0X10-2, with a Nernstian slope of 55.8 ​mV/decade and a limit of detection of 4.3X10-6 ​M. Electrode C exhibits linearity over the concentration range from 8.0X10-6 - 1.0X10-2 ​M, with a Nernstian slope of 61.3 mV/decade and a limit of detection of 4.0X10-6 ​M. These sensors exhibited a fast response time (about 2 ​s) and good stability. Selectivity coefficients, determined by modified separate solution method (MSSM) and separate solution method (SSM), showed high selectivity for vardenafil hydrochloride (VrCl) over a large number of inorganic cations, organic cations, sugars, urine components, and some common drug excipients. The proposed sensors were applied for determination of VrCl in tablets and in spiked urine samples using potentiometric determination and the calibration curve methods. The results obtained were satisfactory with excellent percentage recovery comparable and sometimes better than those obtained by other routine methods for the assay. The CPE is more suitable for commercialization owing to its attractive properties.

Exploitation of o-benzoyl benzoic acid as an efficient electroactive material for selective determination of Cr (III) ions in pharmaceutical samples and industrial waste water using carbon sensor

Herein, for the first time, o-benzoyl benzoic acid has been explored as a promising electroactive material for the fabrication of sensitive, precise and accurate carbon paste electrode (CPE) for selective detection of Cr (III) ion. o-benzoyl benzoic acid (o-BBA) as a sensing material and tricresylphosphate (TCP) as a solvent mediator improved the developed sensor performance to get the Nernstian cationic slope of 20.03 ± 0.11 mV decade−1 within the concentration range of 5.0 × 10−7-1.0 × 10−1 mol L−1. The sensor displayed a fast response time of 12 s reflecting a pH independency over the pH range of 3.1–4.7. Moreover, the reaction between the sensing material and Cr (III) ion on the developed sensor surface was elucidated using the microscopic technique such as scanning electron microscope (SEM) in addition to the energy dispersive X-ray analyzer (EDX). The proposed sensor showed an adequate shelf lifetime (∼33 days). The values of potentiometric selectivity coefficient were obtained by fixed interference and separate solution methods affirming a high distinguishing power of the fabricated sensor toward Cr (III) ions over the other interfering ions. The established sensor could be utilized with a promising success for the Cr (III) ion estimation in the industrial waste water and in the pharmaceutical forms. Additionally, it has been employed as a promising indicator sensor with a superior performance for potentiometric titration of Cr (III) ion against EDTA.

Study of the effect of ionophore carbon chain length on the selectivity of the Nd (III) ion selective electrode

Ion selective electrode method is used for analyzing certain metal ions in a sample with ionophore as the link between two different solutions. The compounds 4-adipoybis (1-phenyl-3-methylpyrazolone-5) (H2AdBP) and 4-sebacoylbis (1-phenyl-3-methylpirazolone-5) (H2SbBP) are the same two types of ionophores but differ in the length of carbon chain. Both ionophores were used in potentiometric analysis of Nd3+ ion and showed that H2AdBP-Nd electrode had a slightly smaller detection limit, namely 1.91 x 10−5M with a sensitivity of 15.9 ± 2.2 mV/decade with a response time of 23 seconds, compared to the H2SbBP-Nd electrode with a detection limit of 2.88 x 10−5M, sensitivity of 21.9 ± 1.1 mV/decade and response time of 22 seconds. The effect of pH on the electrode performance was studied by varying the pH, concentration of ISA KNO3 and composition of the internal solution. Good electrode performance was obtained at pH 3 and the electrode sensitivity increased to pH 4. The electrode selectivity was carried out using a separate solution method (SPM) for the La3+, Ce3+ and Th4+ ions. The determination results of electrode pot showed that ESI-Nd electrode was not selective against La3+ and Ce3+ ions but selective to Th4+ with values < 1.

Potentiometric sensors selective for Cu(II) determination in real water samples and biological fluids based on graphene and MWCNTs modified graphite electrodes

Three newly synthesized Cu(II) ion selective electrodes based on 1,8-dihydoxyanthraquinone (DHAQ), as an ionophore, have been developed. Sensor I was modified with DHAQ only, while sensors II and III were modified with graphene and multi-walled carbon nanotubes (MWCNTs), respectively, in addition to DHAQ to improve conductivity and transduction of chemical signal to electrical signal. Under optimized conditions, the electrodes I, II and III revealed Nernstian slopes of 29.78 ± 0.17, 30.25 ± 0.12, and 30.55 ± 0.19 mV decade-1, respectively, at 25±1° C covering a wide concentration range from 1 × 10-6 to 1 × 10−1 mol L-1 for sensors I and II and from 1 × 10-5 to 1 × 10−1 mol L-1 for sensor III with detection limit values of 8 × 10−7, 5 × 10−7, and 3.3 × 10−6 mol L-1, respectively. The response of the proposed electrodes was very fast and independent of pH in the range of 2.4-6.5 and the response mechanism was studied using IR, SEM and EDX analyses. Selectivity coefficients were determined by applying separate solution method (SSM) and matched potential method (MPM), where the obtained values indicated the good discrimination of Cu(II) from other cations by the proposed sensors. The developed sensors were used successfully for quantitative determination of Cu(II) ions in different matrix of spiked real water samples and biological fluids (urine and serum). These sensors were also used successfully as indicator electrodes in the potentiometric titration of Cu(II) with EDTA.

Development and surface characterization of a bis(aminotriazoles) derivative based renewable carbon paste electrode for selective potentiometric determination of Cr(III) ion in real water samples

Regarding the Cr(III) importance in the industrial, environmental, and even biological systems, development of highly selective and sensitive Cr(III) sensor is a challenge. In this work, a new carbon paste electrochemical sensor containing a synthesized bis(aminotriazoles) derivative namely 1,3-bis[4-amino-5-benzyl-1,2,4-triazol-3-ylsulfanyl]propane (BABTSP) as the Cr(III) selective ionophore was described. Factors affecting sensor’s response were studied and optimized. The proposed sensor exhibited a Nernstian slope of 20.05 ± 0.35 mV decade−1 covering broad linear range of 1.0 × 10−8−5.0 × 10−2 mol L−1 and detection limit was 8.0 × 10−9 mol L−1 for 3 months over pH range of (2.3–5.2) and fast response time (<10 s). The proposed sensor was selective for Cr(III) ions that was confirmed by separate solution method (SSM) and fixed interference method (FIM) . The sensor was precise and reproducible (RSD% range = 0.8–2.45) and effectively used in potentiometric titration of Cr(III) against EDTA and in diverse water samples analysis with recovery data of 96.08–100.2%. The lipophilicity of the applied ionophore was investigated through contact angle measurement technique and average contact angle was 127.59° that resulted in sensor’s mechanical stability. To study the response mechanism and morphology of the prepared sensor, scanning electron microscope (SEM), energy dispersive X-ray (EDX) and FT-IR spectroscopy were used.

A novel porous silicon multi-ions selective electrode based extended gate field effect transistor for sodium, potassium, calcium, and magnesium sensor

One of the most informative parameters of the bio-chemical sensors is the multi-ions selectivity. Characterizing the biocompatible materials with high sensitivity and efficiency for the immobilization and detection of bio-signals and conversion of biochemical signal into quantifiable electronic signal is very important in biosensor research. Extended gate field-effect transistor (EGFET) based on porous silicon (PS) n-type (111) was characterized as sodium, potassium, calcium, and magnesium sensor over the concentration ranges 10−4 to 1 M of the four cations at room temperature. This study extracted the sensitivity of Na+, K+, Ca2+, and Mg2+ in terms of current/voltage sensitivity. Separate Solution Method was used to concept of PS response which suggest a single constant value of the potentiometric selectivity coefficient ($$K_{A,B}^{\text{pot}}$$). Regarding EGFET operation, PS manifested significantly enhanced Na+, K+, Ca2+, and Mg2+ voltage sensitivity of 58.76, 57.91, 34.90, and 31.75 mV/dec, respectively, and they are very close to the theoretical value of Nernst. Moreover, the Na+, K+, Ca2+, and Mg2+ current sensitivity was of 1.09, 1.04, 0.54, and 0.52 (µA)1/2/dec. PS showed high Na+ selectivity towards K+, Ca2+, and Mg2+. The results showed the values of the current/voltage sensitivity have high linearity. Using of PS n-type (111) as multi-ions sensor, and extracting the sensitivity of Na+, K+, Ca2+, and Mg2+ in terms of IDS were not reported in the literature.

Single-Piece All-Solid-State Potential Ion-Selective Electrodes Integrated with Molecularly Imprinted Polymers (MIPs) for Neutral 2,4-Dichlorophenol Assessment.

A novel single-piece all-solid-state ion-selective electrode (SC/ISE) based on carbon-screen printed is introduced. Polyaniline (PANI) is dissolved in a membrane cocktail that contains the same components used for making a conventional ion-selective polyvinyl chloride (PVC) matrix membrane. The membrane, having the PANI, is directly drop-casted on a carbon substrate (screen-printed-carbon electrode). PANI was added to act as an intermediary between the substrate and the membrane for the charge transfer process. Under non-equilibrium sensing mechanism, the sensors revealed high sensitivity towards 2,4-dichlorophenol (DCP) over the linearity range 0.47 to 13 µM and a detection limit 0.13 µm. The selectivity was measured by the modified separate solution method (MSSM) and showed good selectivity towards 2,4-DCP over the most commonly studied ions. All measurements were done in 30 mm Tris buffer solution at a pH 5.0. Using constant-current chronopotentiometry, the potential drift for the proposed electrodes was checked. Improvement in the potential stability of the SPE was observed after the addition of PANI in the sensing membrane as compared to the corresponding coated-wire electrode (membrane without PANI). The applicability of the sensor has been checked by measuring 2,4-DCP in different water samples and the results were compared with the standard HPLC method.

Non-Equilibrium Potential Responses towards Neutral Orcinol Using All-Solid-State Potentiometric Sensors Integrated with Molecularly Imprinted Polymers.

Molecularly imprinted polymer (MIP) receptors have been synthesized, characterized, and applied as new selective receptors in solid-contact ion selective electrodes (ISEs) towards non-dissociated 3,5-dihydroxytoluene (orcinol). Two monomers, namely methacrylic acid (MAA) and acrylamide (AA), were used in the preparation of MIP receptors. Graphene (Gr) was used as the solid contact material between the sensing membrane and the electrical contact substrate. Based on non-equilibrium sensing mechanism, the proposed sensors reveal observably enhanced detection sensitivity towards orcinol with detection limits 1.7 × 10−5 and 3.3 × 10−6 M for sensors based on MIP/MAA and MIP/AA, respectively. The selectivity coefficients measured by the modified separate solution method (MSSM) for the proposed sensors showed good selectivity towards orcinol over most common other phenols and inorganic anions. All measurements were made in the presence of 30 mM phosphate buffer solution (PBS) with a pH of 7.0. Potential stability for the proposed sensors was tested by constant-current chronopotentiometry. No water films were formed between the sensing membrane and the electron conductor substrate. The applicability of MIP/MAA incorporated ISE has been checked by recovery test of orcinol in the presence of soil matrix and by standard addition method.

A New Copper Ionophore N1, N3-Bis [[3,5-Bis(Trifluoromethyl)Phenyl] Carbamothioyl] Isophtalamide for Potentiometric Sensor

A copper ion sensor based on a new bis-thiourea compound N1,N3-bis[[3,5-bis(trifluoromethyl)phenyl]carbamothioyl]isophthalamide (or TPC) as neutral carrier was investigated. The immobilization of the TPC into poly(n-butyl acrylate) (pBA) membrane via drop casting and the sensor was characterized by potentiometry. The sensor fabricated from TPC only showed a good Nernstian response towards copper ion with a sensitivity slope of 28.81±0.53mV/decade in the range of 1.0 × 10-6 - 1.0 × 10-4 M. The limit of detection of this sensor was found to be 6.11 × 10-7 M and with short sensor response time (60 - 80 s). This sensor also demonstrated reversibility and reproducibility with 3.69% and 1.84% (Relative Standard Deviation, RSD), respectively. Based on the separate solution method (SSM), the logarithm selectivity coefficients were better than -2.00 for monovalent, divalent and trivalent cations and this confirmed that the sensor exhibited good selectivity towards copper ion. The sensor could attain optimum function without the need in the inclusion of either lipophilic anions as a membrane additive nor plasticizer as a membrane softener. Thus, these are the main advantages. The addition of lipophilic anions into the pBA membrane could cause the sensitivity and selectivity of the copper ion sensor based on ionophore TPC to deteriorate.

Determination of Selectivity Coefficients of Sodium and Potassium Ion-Selective Electrode Using Porous Silicon N-Type (100) Based Extended Gate Field Effect Transistor

Ion-selective electrode (ISE) was able to accurately detect the ions, precisely for laboratory analysis purposes. The selection of the material varies to select a particular ion, according to the electrode response, and the decisive factor for the optimal selection of ISE for specific ion is the selectivity coefficient. This study used porous silicon (PSi) (100) as an ISE based on extended gate field effect transistor (EGFET) to characterize the selection's preference for sodium (Na+) as a target ion and potassium (K+) is an interference ion. The potential response in the linear region of the EGFET sensor between the detection electrode (PSi) and a reference electrode Ag/AgCl was measured in NaCl, KCl, and a mixed solution of the two salts along ions’ concentration (10-4-1 M) under drain-source voltage 0.3 V at temperature room. The potentiometric selectivity coefficient was calculated by two methods: (1) separate solution method (SSM) at the same activity (0.1 M) and (2) two solution method (TSM). The SSM method, KpotNa,K was 0.581, while the result of TSM method was 0.743. The results showed a slight superiority of Na+ selectivity and acceptable interference resistant for K+.

Beyond the Limit of Ideal Nernst Sensitivity: Ultra-High Sensitivity of Heavy Metal Ion Detection with Ion-Selective High Electron Mobility Transistors

Exposure to heavy metal ions poses grave danger to public health and reliable and affordable water quality monitoring system that can rapidly screen for heavy metal ion contamination is necessary. In this research, we have developed a unique sensing methodology to detect heavy metal ions such as Pb2+ and Hg2+ in water sources, using ion-selective high electron mobility transistor sensor (ISHEMT). A detailed investigation of the sensing and selectivity characteristics of ISHEMT is carried out and a theoretical model is proposed for the illustration of the enhanced sensitivity and selectivity. The high field modulated ISHEMT sensor displays very high sensitivity, much beyond the ideal Nernstian slope, offering very low detection limit (10−10 M for Pb2+ and 10−11 M for Hg2+). The sensing characteristics are not affected by the presence of interfering ions and the selective sensor response has been validated using fixed interference and separate solution methods. These sensor characteristics are superior than the traditional ISE or ISFET sensors, and at par with laboratory standard technologies like ICP-MS. The miniaturized, inexpensive and user-friendly sensor technology can provide consumers with an affordable and convenient means of securing safe and contamination free water and food consumption.

Development of New Cs+ Ion‐Selective Electrode with Alkyl‐Bridged Calix[4]arene Crown‐6 Compounds for the Determination of Cs+ in Nuclear Waste Streams

AbstractA new liquid membrane based Ion Selective Electrodes (ISE) for Cs+ employing three 1,3 cycloalkyloxy bridged calix[4]arene crown 6 ether compounds (L1: cyclooctyloxy, L2: cyclodecyloxy, L3: cyclotetradecyloxy) as ionophores were developed. The best response was observed when L3 was used as an ionophore. The cation exchange resin DOWEX‐50 W was used to maintain low activity of Cs+ in inner filling solution (IFS) to improve the performance. With optimized IFS, Nernstian response (56.3 mV/decade of Cs+) over the concentration range 10−7 to 10−2 M of Cs+ was observed. Studies were also carried out to develop all solid contact Cs+ ISE employing gold‐ polyaniline composites as a transducer. Superior response for Cs+ was observed with IFS based ISE. The developed ISE showed detection limit of 3.7x10−8 M Cs+ with response time less than 20 seconds. Separate solution method was applied to determine selectivity for Cs+ over alkali, alkaline earth and transition metal ions. The response of ISE for Cs+ was fairly constant over the pH range 4–11. The concentration of Cs+ was determined in two simulated high level active waste solutions and spiked tap water samples and results agreed well with atomic absorption spectroscopy (AAS) values and expected values, respectively.