The Origin of the Non-Constancy of the Bulk Resistance of Ion-Selective Electrode Membranes within the Nernstian Response Range.
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ABSTRACT:
SUBMITTER: Keresten V
PROVIDER: S-EPMC8150337 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Ionophore-doped sensing membranes exhibit greater selectivities and wider measuring ranges if their membrane matrixes are noncoordinating and solvate interfering ions poorly. This is particularly true for fluorous phases, which are the least polar and polarizable condensed phases known. In this work, fluorous membrane matrixes were used to prepare silver ion-selective electrodes (ISEs). Sensing membranes composed of perfluoroperhydrophenanthrene, sodium tetrakis[3,5-bis(perfluorohexyl) phenyl]borate, and one of four fluorophilic Ag(+)-selective ionophores with one or two thioether groups were investigated. All electrodes exhibited Nernstian responses to Ag(+) in a wide range of concentrations. Their selectivities for Ag(+) over interfering ions were found to depend on host preorganization and the length of the -(CH(2))(n)- spacers separating the coordinating thioether group from the strongly electron withdrawing perfluoroalkyl groups. ISEs based on the most selective of the four ionophores, that is, 1,3-bis(perfluorodecylethylthiomethyl)benzene, provided much higher selectivities for Ag(+) over many alkaline and heavy metal ions than most Ag(+) ISEs reported in the literature (e.g., log K(Ag,J)(pot) for K(+), -11.6; Pb(2+), -10.2; Cu(2+), -13.0; Cd(2+), -13.2). Moreover, the use of this ionophore with a linear perfluorooligoether as membrane matrix and solid contacts consisting of three-dimensionally ordered macroporous (3DOM) carbon resulted in a detection limit for Ag(+) of 4.1 ppt (3.8 × 10(-1)1 M).
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Project description:Because of their low polarity and polarizability, fluorous sensing membranes are both hydrophobic and lipophobic and exhibit very high ion selectivities. Here, we report on a new fluorous-membrane ion-selective electrode (ISE) with a wide sensing range centered around physiologically relevant pH values. The fluorophilic tris[perfluoro(octyl)butyl]amine (N[(CH2)4Rf8]3) was synthesized and tested as a new H+ ionophore using a redesigned electrode body that provides excellent mechanical sealing and much improved measurement reliability. In a challenging 1 M KCl background, these fluorous-phase ISEs exhibit a sensing range from pH 2.2 to 11.2, which is one of the widest working ranges reported to date for ionophore-based H+ ISEs. High selectivities against common interfering ions such as K+, Na+, and Ca2+ were determined (selectivity coefficients: logK H, K pot = - 11.6; logK H, Na pot = - 12.4; logK H, Ca pot < - 10.2). The use of the N[(CH2)4Rf8]3 ionophore with its -(CH2)4- spacers separating the amino group from the strongly electron-withdrawing perfluorooctyl groups improved the potentiometric selectivity as compared to the less basic tris[perfluoro(octyl)propyl]amine ionophore. The use of N[(CH2)4Rf8]3 also made the ISE less prone to counter anion failure (i.e., Donnan failure) at low pH than the use of tris[perfluoro(octyl)pentyl]amine with its longer -(CH2)5- spacers, which more effectively shield the amino center from the perfluorooctyl groups. In addition, we exposed both conventional plasticized PVC-phase pH ISEs and fluorous-phase pH ISEs to 10% serum for 5 days. Results show that the PVC-phase ISEs lost selectivity while their fluorous-phase counterparts did not.
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Project description:Wireless, flexible, ion-selective electrodes (ISEs) are of great interest in the development of wearable health monitors and clinical systems. Existing film-based electrochemical sensors, however, still have practical limitations due to poor electrical contact and material-interfacial leakage. Here, we introduce a wireless, flexible film-based system with a highly selective, stable, and reliable sodium sensor. A flexible and hydrophobic composite with carbon black and soft elastomer serves as an ion-to-electron transducer offering cost efficiency, design simplicity, and long-term stability. The sensor package demonstrates repeatable analysis of selective sodium detection in saliva with good sensitivity (56.1 mV/decade), stability (0.53 mV/h), and selectivity coefficient of sodium against potassium (-3.0). The film ISEs have an additional membrane coating that provides reinforced stability for the sensor upon mechanical bending. Collectively, the comprehensive study of materials, surface chemistry, and sensor design in this work shows the potential of the wireless flexible sensor system for low-profile wearable applications.
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Project description:In this study, we demonstrated the unique capability of carbon-based ion-selective electrode (ISE) to perform highly sensitive square wave anodic stripping voltammetry, while maintaining all the properties of an ISE, in terms of sensitivity, detection limit, response time and selectivity. Square wave anodic stripping voltammetry involves deposition and dissolution steps of metal ions, which means adsorption and desorption of metal ions on the conductive ion-selective membrane without losing its ion-sensing property. To demonstrate this capability, we chose a Ca2+ ion-selective microelectrode (μISE) as a potentiometric method and Cu2+-stripping voltammetry as an amperometric method. The carbon-based ISE surface is capable of quantifying nanomolar to micromolar Cu2+ in both a standard acetate buffer and a complex water sample. The Ca2+-μISE also showed a Nernstian slope of 29 mV / log [Ca2+] and a detection limit of 1 μM within the linear range of 1 μM to 10 mM. It thus opens an opportunity to use the low detection limit of anodic stripping voltammetry and the high selectivity of ISE-based potentiometry.
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Project description:Phosphorus is not only an import nutrient to aquatic habitats, but it also acts as a growth inhibitor in aquatic ecosystems; however, it also aggravates environmental issues, such as eutrophication. There is a growing interest in rapid phosphorus detection to manage and protect water resources. Due to the large molecular structure and high hydration energy of phosphate ions, ion-selective electrodes (ISEs) remain in their infancy for real-time measurements in terms of practical application. In this study, a newly developed ionophore based on a biomimetic nicotinamide functional group was used to detect phosphate selectively, displaying efficient binding through charge interactions and hydrogen bonds. The ISE membrane containing silicone rubber demonstrated an effective detection performance over a long period of time. With a dynamic range between 10-6 and 10-2 M and a limit of detection of 0.85 × 10-6 M (26 μg/L), the newly synthesized ISE membranes demonstrated selectivity for phosphate ions over other ions, including acetate, sulfate, and chloride.
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Project description:Lithium holds immense significance in propelling sustainable energy and environmental systems forward. However, existing sensors used for lithium monitoring encounter issues concerning their selectivity and long-term durability. Addressing these challenges is crucial to ensure accurate and reliable lithium measurements during the lithium recovery processes. In response to these concerns, this study proposes a novel approach involving the use of an MXene composite membrane with incorporated poly(sodium 4-styrenesulfonate) (PSS) as an antibiofouling layer on the Li+ ion selective electrode (ISE) sensors. The resulting MXene-PSS Li+ ISE sensor demonstrates exceptional electrochemical performance, showcasing a superior slope (59.42 mV/dec), lower detection limit (10-7.2 M), quicker response time (∼10 s), higher selectivity to Na+ (-2.37) and K+ (-2.54), and reduced impedance (106.9 kΩ) when compared to conventional Li+ ISE sensors. These improvements are attributed to the unique electronic conductivity and layered structure of the MXene-PSS nanosheet coating layer. In addition, the study exhibits the long-term accuracy and durability of the MXene-PSS Li+ ISE sensor by subjecting it to real wastewater testing for 14 days, resulting in sensor reading errors of less than 10% when compared to laboratory validation results. This research highlights the great potential of MXene nanosheet coatings in advancing sensor technology, particularly in challenging applications, such as detecting emerging contaminants and developing implantable biosensors. The findings offer promising prospects for future advancements in sensor technology, particularly in the context of sustainable energy and environmental monitoring.
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Project description:In this work, the effect of ion-selective membranes on the detailed carbon balance was systematically analyzed for high-rate CO2 reduction in GDE-type flow electrolyzers. By using different ion-selective membranes, we show nearly identical catalytic selectivity for CO2 reduction, which is primarily due to a similar local reaction environment created at the cathode/electrolyte interface via the introduction of a catholyte layer. In addition, based on a systematic exploration of gases released from electrolytes and the dynamic change of electrolyte speciation, we demonstrate the explicit discrepancy in carbon balance paths for the captured CO2 at the cathode/catholyte interface via reaction with OH- when using different ion-selective membranes: (i) the captured CO2 could be transported through an anion exchange membrane in the form of CO3 2-, subsequently releasing CO2 along with O2 in the anolyte, and (ii) with a cation exchange membrane, the captured CO2 would be accumulated in the catholyte in the form of CO3 2-, while (iii) with the use of a bipolar membrane, the captured CO2 could be released at the catholyte/membrane interface in the form of gaseous CO2. The unique carbon balance path for each type of membrane is linked to ion species transported through the membranes.
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Project description:BackgroundChloride measurement is crucial for calculating the anion gap. Bicarbonate can interfere with chloride measurements; however, there is no information on the specific types of electrodes affected or the changes in bicarbonate non-selectivity over time. We evaluated the interference of bicarbonate on chloride measurements using different electrodes and the stability of this interference over time.MethodsThe effect of bicarbonate on chloride measured with electrodes of various manufacturers was assessed. When non-selectivity toward bicarbonate was observed, the stability of this interference during the electrode's lifetime was explored. The impact of the bicarbonate concentration on the calibrator was also evaluated.ResultsNon-selectivity was observed for electrodes using quaternary ammonium salts (Beckman Coulter, Siemens, and Roche), with overestimated or underestimated chloride values observed at high or low bicarbonate concentrations, respectively. The degree of selectivity varied among electrodes. With the Roche electrode, interference became more pronounced over time, whereas the Siemens electrode appeared to gain selectivity during its lifetime. For the Roche system, adjusting the calibrator's bicarbonate concentration from 30 mmol/L to 20-24 mmol/L reduced the number of samples with unacceptable bias (>3%) from 77.3% to 12.6%. Lot-to-lot variations in the calibrator bicarbonate concentration increased the uncertainty of chloride measurements.ConclusionsThe extent of bicarbonate-induced error varied according to the type, manufacturer, and wear of the electrode; the bicarbonate concentration in the calibrators and the tested sample; and the chloride content. Laboratories should be aware of the impact of bicarbonate on routine chloride measurements to establish appropriate QC procedures.
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Project description:The solid contact ion-selective electrode (ISE) is a promising skin-interfaced monitoring system for sweat ions. Despite a growing number of on-body usages of ISE with fancy new materials and device fabrications, there are very few reports attempting to validate ISE results with a gold standard technique. For this purpose, this work uses inductively coupled plasma-optical emission spectrometry (ICP-OES) as a reference technique to conduct a direct evaluation of the sweat sodium and potassium ion levels obtained by ISE in an off-body approach. Eight healthy male subjects were recruited to collect exercise-induced sweat. It was found that sweat sodium and potassium ions present a rather wide concentration range. The sweat sodium concentration did not vary greatly in an exercise period of half an hour, while the sweat potassium concentration typically decreased with exercise. Mineral drink intake had no clear impact on the sweat sodium level, but increased the sweat potassium level. A paired t-test and mean absolute relative difference (MARD) analysis, a method typically used for evaluating the performance of glucometers, was employed to compare the results of ISE and ICP-OES. The statistical analysis validated the feasibility of ISE for measuring sweat ions, although better accuracy is required. Our data suggests that overweight subjects are likely to possess a higher sweat sodium level.
| S-EPMC9026306 | biostudies-literature