Ion-selective Potentiometry Research Articles

Association of perinatal exposition to xenobiotics with kidney volume at birth.

The state of Aguascalientes has the highest prevalence of kidney failure in young adults. A low nephron endowment has been suggested as a possible etiology. This study aims to evaluate the association between exposure to xenobiotics and low kidney volume (KV) at birth. This is a cross-sectional, observational, and descriptive study of at-term pregnant women, with no comorbidities. We collected the mother´s urine (MU), amniotic fluid (AF), and neonate´s urine (NU). Metals and non-metals were measured with inductively coupled plasma mass spectrometry, pesticides were determined with high-performance liquid chromatography, and fluoride by ion-selective potentiometry. The total KV adjusted by body surface area (TKVBS) was calculated based on the kidney ultrasound. Between March-2022 and July-2023, we included 299 women with an average of 24.2 years (± 5.1). 54.2% of neonates were male with an average weight of 3,266 gr (± 399).Factors associated with the TKVBS ≤ 5 percentile were female sex, weight gain during the pregnancy, glomerular filtration rate, methomyl concentration in AF (Odds ratio 7.41, 95% confidence interval 2.31 - 23.8, p= 0.001), 2,4-Dichlorophenoxyacetic (2,4-D) >10 ng/ml in AF (4.99, 1.58 - 15.7, p= 0.002), MU (6.1, 1.9 - 19.7, p= 0.002), and NU (5.1, 1.10 - 26.2, p= 0.023) and fluoride in MU (5.1, 1.10 - 23.5, p= 0.010), and AF (6.76, 1.28 - 35.7, p=0.024). In all matrices (MU, AF and NU) exposure to pesticides was also significantly associated with greater concentrations of electrolytes (Na, K, Ca, PO4 and Mg and oligo-elements (Zn and Fe). In neonates born to at-term women with no comorbidities, the presence of pesticides and fluoride was associated with low KV. The significant loss of electrolytes and oligoelements associated with pesticides suggests proximal tubulopathy.

Stability of Graphene/Nafion Composite in PEM FC Electrodes.

Ensuring the stable operation of proton exchange membrane fuel cells is conducive to their real-world application. A promising direction for stabilizing electrodes is the stabilization of the ionomer via the formation of surface compounds with graphene. A comprehensive study of the (electrochemical, chemical, and thermal) stability of composites for fuel cell electrodes containing a modifying additive of few-layer graphene was carried out. Electrochemical stability was studied by cycling the potential on a disk electrode for 5000 cycles. Chemical stability was assessed via the resistance of the composites to H2O2 treatment using ion-selective potentiometry. Thermal stability was studied using differential thermal analysis. Composites were characterized by UV-Vis spectroscopy, Raman spectroscopy, EDX, and SEM. It was shown that graphene inhibits Nafion degradation when exposed to heat. Contrariwise, Nafion is corrosive to graphene. During electrochemical and chemical exposure, the determining change for carbon-rich composites is the carbon loss (oxidation) of the carbon material. In the case of carbon-poor composites, the removal of fluorine and sulfur from the Nafion polymer with their partial replacement by oxygen prevails. In all cases, the F/S ratio is stable. The dispersity of Nafion in a sample affects its chemical stability more than the G/Nafion ratio does.

Ion-Selective Potentiometry with Plasma-Initiated Covalent Attachment of Sensing Membranes onto Inert Polymeric Substrates and Carbon Solid Contacts.

The physical delamination of the sensing membrane from underlying electrode bodies and electron conductors limits sensor lifetimes and long-term monitoring with ion-selective electrodes (ISEs). To address this problem, we developed two plasma-initiated graft polymerization methods that attach ionophore-doped polymethacrylate sensing membranes covalently to high-surface-area carbons that serve as the conducting solid contact as well as to polypropylene, poly(ethylene-co-tetrafluoroethylene), and polyurethane as the inert polymeric electrode body materials. The first strategy consists of depositing the precursor solution for the preparation of the sensing membranes onto the platform substrates with the solid contact carbon, followed by exposure to an argon plasma, which results in surface-grafting of the in situ polymerized sensing membrane. Using the second strategy, the polymeric platform substrate is pretreated with argon plasma and subsequently exposed to ambient oxygen, forming hydroperoxide groups on the surface. Those functionalities are then used for the initiation of photoinitiated graft polymerization of the sensing membrane. Attenuated total reflection-Fourier transform infrared spectroscopy, water contact angle measurements, and delamination tests confirm the covalent attachment of the in situ polymerized sensing membranes onto the polymeric substrates. Using membrane precursor solutions comprising, in addition to decyl methacrylate and a cross-linker, also 2-(diisopropylamino)ethyl methacrylate as a covalently attachable H+ ionophore and tetrakis(pentafluorophenyl)borate as ionic sites, both plasma-based fabrication methods produced electrodes that responded to pH in a Nernstian fashion, with the high selectivity expected for ionophore-based ISEs.

Soft Drinks as a Dietary Source of Fluoride Exposure

High fluoride exposures can lead to adverse effects such as dental and bone fluorosis, as well as endocrine and cognitive developmental problems. Water is the main dietary source of this ion, although significant concentrations have also been detected in other beverages widely consumed by the population such as soft drinks. A total of 200 soft drink samples (60 flavoured, 70 extracts, 60 fruit juice and 10 soft drinks) were analysed by fluoride ion selective potentiometry. A consumption of 330 mL was estimated for exposure assessment and subsequent F-risk assessment by soft drink consumption. The highest average concentration was found in extract soft drinks (2.45 ± 1.15 mg/L), followed by flavoured (1.71 ± 2.29 mg/L) and carbonated soft drinks (1.38 ± 0.40 mg/L), while the lowest was found in fruit juice soft drinks (1.09 ± 0.62 mg/L). The flavours with the highest concentration were tea-melon and tea-passion fruit with 3.66 ± 0.40 and 3.17 ± 0.56 mg/L respectively and the lowest was lemon flavour with 0.69 mg/L. The contribution of these beverages, considering the UL (Upper level) reference values set by EFSA (European Food Safety Authority) are between 3.28–41.78%, depending on age group and sex.

Fluoride Levels in Supply Water from the Canary Islands Region

The Canary Islands, located in the Atlantic Ocean, are an archipelago of volcanic origin which, for decades, has been affected by natural fluoride contamination in the water supply of some of its islands, mainly the island of Tenerife. In addition, recent volcanic eruptions in the archipelago and the increased demand for water supply have led to an increase in the fluoride content in other areas which, historically, were not affected. Fluoride content was determined in 274 water supply samples from the most populated islands of the Canary Islands (Tenerife and Gran Canaria) collected during the months of June 2021 to May 2022. The samples were analysed by fluoride ion selective potentiometry. The highest concentrations in Tenerife were found in the municipalities of Sauzal (7.00 mg/L) and Tegueste (5.39 mg/L), both water samples are over the parametric value of 1.5 mg/L set in the supply water legislation. In the Gran Canaria Island, the highest fluoride levels were found in Valsequillo and Mogán with 1.44 mg/L in both locations, but under the parametric fluoride value abovementioned. Consumption of just 1 L of water per day in the El Sauzal area would result in a contribution rate of 77% for adults and children over 15 years of age (Upper Level value of 7 mg/day) and 108% for children 9-14 years of age (UL value of 5 mg/day). The contribution rates increase considerably, reaching or exceeding 100% of the reference value (UL) with increasing consumption of 1 to 2 L of water per day. Therefore, it is considered that there is a health risk of overexposure to fluoride on the island of Tenerife. In the case of the island of Gran Canaria, it has been shown that even the consumption of 2 litres of water per day does not confer contribution rates that pose a health risk.

Adverse maternofoetal outcomes associated with ionised calcaemia, total calcaemia, albuminaemia, and calcium supplementation in pregnancy: Analysis from a resource-limited setting.

Disorders of total calcium (tCa) in pregnancy have been associated with adverse maternofoetal outcomes. However, studies evaluating this from the viewpoint of ionised calcaemia are practically inexistent. This study estimates the prevalence of some adverse maternal and foetal outcomes and the potential effect of ionised calcium (iCa), tCa, albumin and calcium supplementation on some maternofoetal outcomes. A cross-sectional study was conducted among 1074 pregnant women in late pregnancy from four health facilities in the Nkongsamba Health District. Data were collected by interview, analysis of maternal blood samples and measurement of maternal and foetal parameters. Total calcaemia and albuminaemia were measured by atomic absorption spectrophotometry, while iCa and pH were measured using ion-selective potentiometry. Associations were measured using the odds ratio in simple and multiple logistic regression. The prevalence of low birth weight, macrosomia, and hypertension in pregnancy was 6.27 [4.97-7.89]%, 4.78 [3.65-7.89]%, 10.24 [8.57-12.20]%, respectively. Following multiple logistic regression, women with iCa levels ≤ 1.31mmol/L had significantly increased odds of hypertension in pregnancy (AOR = 2.47 [1.63-3.74], p-value = 0.000), having babies with low birth weight (AOR = 2.02[1.33-3.61], p-value = 0.002), low birth length (AOR = 2.00 [1.34-2.99], p-value = 0.001), low brachial circumference (AOR = 1.41[1.10-1.81], p-value = 0.007), first minute Apgar score < 7 (AOR = 3.08[1.70-5.59], p-value = 0.000) and fifth minute Apgar score < 7 (AOR = 2.86[1.32-6.16], p-value = 0.007). Ionised calcaemia had no significant association with maternal body mass index immediately after birth and the head circumference of the baby. Total calcaemia was found to have no significant association with any of the selected outcomes, while women with total albuminaemia ≤ 30mg/L had significantly higher odds of having babies with low birth weight (AOR = 3.40[1.96-5.91], p-value = 0.000), and Apgar scores < 7 at the first (AOR = 2.07[1.16-3.70], p-value = 0.013). Calcium supplementation showed no significant association with any of the selected outcomes except for the first (OR = 0.42[0.24-0.72], p-value = 0.002) and fifth minute Apgar score (OR = 0.25[0.12-0.50], p-value = 0.000). The prevalence of low birth weight, macrosomia, and hypertension in pregnancy was 6.27 [4.97-7.89]%, 4.78 [3.65-7.89]%, 10.24 [8.57-12.20]%, respectively. Maternal iCa levels ≤ 1.31mmol/L significantly increase the odds of having babies with low birth weight, low birth length, low brachial circumference at birth, low Apgar scores at the first and fifth minutes and maternal hypertension in pregnancy. Low maternal albuminaemia is significantly associated with low birth weight, and Apgar score < 7 at the first minute. None f the selected maternofoetal outcomes directly depend on total calcaemia, given that none of the associations was statistically significant. Even though iCa levels remain relatively normal in normal pregnancies, it remains the strongest predictor of foetal outcomes. Calcium supplementation significantly improves the Apgar scores at the first and fifth minute. Routine pregnancy follow-up should include evaluating maternal calcaemic states, particularly the ionised fraction, to detect the low-normal concentrations likely to impact maternal and foetal outcomes. Normal iCa levels for pregnant women need revisiting.

Detection of Marginally Discriminated Ions with Differential Solid Contact Ion-Selective Electrodes

A differential sensor is reported for decreasing the interference from multiple ionic and non-ionic species in droplet-sized samples, hence lowering the detection limit for ions that are particularly hard to measure by conventional ion-selective potentiometry. We believe that the proposed approach represents significant progress beyond state-of-the-art by making the application of ion-selective membranes possible for ions that do not have selective ionophores. Two solid contact ion-selective electrodes (SCISEs) are utilized, which are prepared similarly, except for adding ionophore to one of the membranes. We show experimentally and theoretically that a significant signal is observed only when the analyte ion is present in the sample solution. The dynamic response of the sensor is investigated theoretically by Nernst-Planck-Poisson finite element simulations. Symbolic regression is used to generate human-readable expressions. Differential SCISEs are tested under potentiometric and amperometric conditions. While a large potential response is seen in the conventional SCISE vs reference electrode setup at high concentrations of interfering ions, the signal of interfering species is eliminated in the differential SCISE setup. Consequently, it is possible to measure a few μM levels of ammonium in droplets without the interference of potassium using an ionophore that is not especially selective for ammonium over potassium.

Dependence of the Solubility of Basic Copper Acetate on the Concentration of the Solution and the pH of the Suspension

Physicochemical equilibria in an aqueous suspension of basic copper acetate are studied via ion-selective potentiometry at 20°С. Equations are obtained that link the solubility product for basic copper acetate to the total content of copper in the solution and the pH of the suspension.

Flexible Electrochemical Bioelectronics: The Rise of In Situ Bioanalysis.

The amalgamation of flexible electronics in biological systems has shaped the way health and medicine are administered. The growing field of flexible electrochemical bioelectronics enables the in situ quantification of a variety of chemical constituents present in the human body and holds great promise for personalized health monitoring owing to its unique advantages such as inherent wearability, high sensitivity, high selectivity, and low cost. It represents a promising alternative to probe biomarkers in the human body in a simpler method compared to conventional instrumental analytical techniques. Various bioanalytical technologies are employed in flexible electrochemical bioelectronics, including ion-selective potentiometry, enzymatic amperometry, potential sweep voltammetry, field-effect transistors, affinity-based biosensing, as well as biofuel cells. Recent key innovations in flexible electrochemical bioelectronics from electrochemical sensing modalities, materials, systems, fabrication, to applications are summarized and highlighted. The challenges and opportunities in this field moving forward toward future preventive and personalized medicine devices are also discussed.

Heavy-Metal Extraction from Wastewater by Means of Iron Nanopowder

Two methods of producing iron nanopowder that is resistant to atmospheric oxidation are considered. The properties of the nanopowder are investigated by thermogravimetric analysis, X-ray diffraction analysis, and scanning electron microscopy. Its specific surface is measured by low-temperature nitrogen absorption. The effectiveness of the iron nanopowder in the removal of heavy metals (lead, copper, and zinc) from industrial wastewater is assessed for model solutions and for wastewater from the gas-processing system in the blast-furnace shop at PAO Severstal. The concentrations of dissolved ions are determined by ion-selective potentiometry and atomic-emission spectrometry. For purposes of comparison, experiments are conducted with natural sorbents (shungite, glauconite) and artificially activated K coal.

Torrefaction of a solid recovered fuel (SRF) to improve the fuel properties for gasification processes

This work studies the torrefaction of a solid recovered fuel (SRF) and its effect on the fuel properties for gasification. The SRF (namely FL) was torrefied at two temperatures (290°C and 320°C) in a pilot auger reactor (capacity of up to 100kg/h) and evaluated as a gasification feedstock. This evaluation included the characterization of the obtained torrefied materials (FL290 and FL320) and several gasification tests in a bench-scale fluidized bed reactor. These tests were performed with different gasification agents (air and oxygen/steam) and bed materials (sand, dolomite and olivine) at similar experimental conditions (T=850°C and ER∼0.3). The evaluation of the gasification performance was presented in terms of product yields and gas composition together with the release of contaminants. Tar species (polycyclic aromatic hydrocarbons) and minor contaminants (H2S, HCl, HCN and NH3) were analysed by gas chromatography and ion-selective potentiometry, respectively. Additionally, the calculation of the process efficiency (gasification and its combination with torrefaction) based on the energy content of the producer gas and a preliminary cost analysis that evaluate the main benefits and drawbacks of the torrefaction process are included. The results indicated that the torrefaction process improved the SRF gasification parameters (lower tar, higher H2/CO ratio, carbon conversion, etc.) and strongly affected the presence of HCl in the producer gas. However, the preliminary cost analysis advised the combination of both technologies only under certain gasification conditions.

The role of PVP in the bioavailability of Ag from the PVP-stabilized Ag nanoparticle suspension

We assessed the bioavailability of Ag from Ag nanoparticles (NPs), stabilized with polyvinylpyrrolidone (PVP), to terrestrial isopods which were exposed to 10, 100 and 1000 μg Ag NPs/g of dry food. Different Ag species were determined in the NP suspension that was fed to isopods: (i) total Ag by atomic absorption spectroscopy, (ii) the sum of Ag-PVP complexes and free Ag+ by anodic stripping voltammetry at the bismuth-film electrode, and (iii) free Ag+ by ion-selective potentiometry. The amounts of Ag species in the consumed food were compared to the masses of Ag accumulated in the isopod digestive glands. Our results show that all three Ag species (Ag NPs, Ag-PVP complexes and free Ag+) could be the source of bioaccumulated Ag, but to various degrees depending on the exposure concentration and transformations in the digestive system. We provide a proof that (i) Ag NPs dissolve and Ag-PVP complexes dissociate in the isopod digestive tract; (ii) the concentration of free Ag+ in the suspension offered to the test organisms is not the only measure of bioavailable Ag. The type of NP stabilizer along with the NP transformations in the digestive system needs to be considered in the creation of new computational models of the nanomaterial fate.

An Explicit Formulation Approach for the Analysis of Calcium Binding to EF-Hand Proteins Using Isothermal Titration Calorimetry

We present an improved and extended version of a recently proposed mathematical approach for modeling isotherms of ligand-to-macromolecule binding from isothermal titration calorimetry. Our approach uses ordinary differential equations, solved implicitly and numerically as initial value problems, to provide a quantitative description of the fraction bound of each competing member of a complex mixture of macromolecules from the basis of general binding polynomials. This approach greatly simplifies the formulation of complex binding models. In addition to our generalized, model-free approach, we have introduced a mathematical treatment for the case where ligand is present before the onset of the titration, essential for data analysis when complete removal of the binding partner may disrupt the structural and functional characteristics of the macromolecule. Demonstration programs playable on a freely available software platform are provided. Our method is experimentally validated with classic calcium (Ca2+) ion-selective potentiometry and isotherms of Ca2+ binding to a mixture of chelators with and without residual ligand present in the reaction vessel. Finally, we simulate and compare experimental data fits for the binding isotherms of Ca2+ binding to its canonical binding site (EF-hand domain) of polycystin 2, a Ca2+-dependent channel with relevance to polycystic kidney disease.

Secondary Hyperparathyroidism Induced by Plateletpheresis in Donors As a Result of Divalent Cationic Chelation by Citrate.

AbstractAbstract 2284 Background:Apheresis is an efficient method to collect specific blood components such as platelets, leukocytes, plasma and stem cells. Its advantages include: the collection of standardized and high-quality blood products and a higher collection frequency. However, apheresis is usually accompanied by acute metabolic changes (specially in serum calcium and magnesium concentrations) due to citrate infusion during the whole procedure. Aim:To compare pre and post-plateletpheresis serum level concentrations of calcium, magnesium, zinc, copper and parathyroid hormone among donors and correlate these levels with symptoms that donors may experience during the procedure performance. Materials and Methods:This is a prospective study including 105 healthy plateletpheresis donors who attended the National Cancer Institute. Basal and post-procedure serum levels of parathyroid hormone (PTH), calcium (Ca), magnesium (Mg), zinc (Zn) and copper (Cu) were measured by ion selective potentiometry (Ca), final dot (Mg), atomic absorption (Cu, Zn) and solid phase two site chemoluminiscence (PTH) methods. In case of adverse reactions, a blood sample was drawn immediately in order to analyze concentrations of such hormone and minerals. We intended to correlate both, diet and adverse reactions with serum levels of aforementioned elements. Statistical analysis was performed by chi-square and ANOVA. Protocol was approved by the institutional ethical and research committee. Results:One hundred and five consecutive donors were included in the study conducted from June 28th through July 27th, 2012. There were 68 males and 37 females. Median age was 31 years (range 18–56). Pre and post-apheresis PTH, Ca, Mg, Zn and Cu serum levels are shown in table 1. Furthermore we found significant differences in women older than 30 years but did not find any relationship between donors’ symptoms and diet. Conclusions:Plateletpheresis induced a secondary hyperparathyroidism state resulting from chelation of calcium and magnesium. We demonstrated that Cu was also chelated by citrate. These results urges us to assess the kinetics of these metabolic changes as well as to follow a cohort of donors with bone densitometry in order to assure that frequent and chronic infusion of citrate during plateletpheresis donations does not become a long-term risk for osteopenia and osteoporosis as already suggested by some authors1,2. If such a risk is demonstrated other preventive measures must be implemented like: 1.- To restrict the number of apheresis donations per person and 2.- To develop new and safer anticoagulants to be used during the apheresis procedures.MediaNDeviation typeError tip. De la mediapCa pre mg/dL9.331050.460.0450.000Ca post mg/dL7.871051.480.144Mg pre mg/dL2.151030.1540.0150.000Mg post mg/dL1.91030.2540.025PTH pre pg/mL50.6110119.361.920.000PTH post pg/mL122.8210142.644.24Zn pre ug/L978.43100160.1116.010.061Zn post ug/L502.9100147.2614.7Cu pre ug/L100999253.8725.510.000Cu post ug/L865.599183.4718.43 Disclosures:No relevant conflicts of interest to declare.

Association of quaternized poly(4-vinylpyridine) and sodium dodecyl sulfate in water-alcohol solvents

Complexation of a cationic polyelectrolyte (partially quaternized poly(4-vinylpyridine)) and the anionic surfactant sodium dodecyl sulfate in aqueous-organic solutions with different ratios of the components is studied by ion-selective potentiometry, viscometry, spectrophotometry, and microelectrophoresis. Effects of the nature and composition of water-alcohol (methanol, ethanol, and isopropanol) mixtures on the parameters of binding of surfactant ions by polyelectrolytes, the hydrodynamic properties of complexes, and the phase state of the system are examined. The addition of small amounts of ethanol and isopropanol to water (20 vol % ethanol and 10 vol % isopropanol) leads to an increase in the intensity of sodium dodecyl sulfate binding by the polyelectrolyte. The addition of up to 30 vol % methanol is not accompanied by a change in the character of surfactant binding relative to that of the aqueous solution. The relationship between the complexing behavior of the polyelectrolyte and the structural features of mixed solvents is discussed.

Coated wire thorium ion selective electrode: Part I

Coated wire ion selective electrode for thorium ion selective potentiometry was developed. Thorium ion selective coated wire electrodes were prepared by depositing a membrane comprising of Aliquat-336 loaded with Th(NO3)62− ions and poly vinyl chloride in varying proportion. A linear near-Nernstian response with a slope of −29.5 ± 0.3 mV over thorium concentration range of 1 × 10−1–3 × 10−5 M in constant total nitrate concentration of 6 M was obtained for the electrodes of almost all the composition studied. In spite of small drift in response potential from composition to composition, day to day as well as from electrode to electrode, the slope of potential response line was constant within experimental error. Moreover, the electrode once prepared could be conveniently used over a period of one and half month.

Enantiomeric discrimination of chiral crown ether ionophores containing phenazine subcyclic unit by ion-selective potentiometry

In this paper the enatiomeric selectivity of two chiral phenazino-18-crown-6 ether hosts ((R,R)-\textbf1 and (R,R)-\textbf2) is quantified. These hosts were incorporated into plasticized PVC membranes and used as recognition elements of ion-selective electrodes. The potentiometric response towards the two enantiomers of 1-phenylethylammonium ions (PEA+) was measured. Potentiometric selectivity coefficients were calculated which reflect the ratio of the stability constants of the diastereomeric complexes. Ligand (R,R)-\textbf1 does not show enantiomeric recognition, while ligand (R,R)-\textbf2 has a slight preference for the (S)-(-) enantiomer over the (R)-(+) enantiomer manifested by a selectivity coefficient of 0.77. The results were compared to enantioselectivity patterns of the ligands towards &#945; -(1-naphthyl)ethyl ammonium perchlorate (NEA+ClO4-) enantiomers measured by circular dichroism and by 1H NMR titrations.

Fluorous polymeric membranes for ionophore-based ion-selective potentiometry: how inert is Teflon AF?

Fluorous media are the least polar and polarizable condensed phases known. Their use as membrane materials considerably increases the selectivity and robustness of ion-selective electrodes (ISEs). In this research, a fluorous amorphous perfluoropolymer was used for the first time as a matrix for an ISE membrane. Electrodes for pH measurements with membranes composed of poly[4,5-difluoro-2,2-bis(trifluoromethyl)-1,3-dioxole]-co-poly(tetrafluoroethylene) (87% dioxole monomer content; known as Teflon AF2400) as polymer matrix, a linear perfluorooligoether as plasticizer, sodium tetrakis[3,5-bis(perfluorohexyl)phenyl]borate providing for ionic sites, and bis[(perfluorooctyl)propyl]-2,2,2-trifluoroethylamine as H+ ionophore were investigated. All electrodes had excellent potentiometric selectivities, showed Nernstian responses to H+ over a wide pH range, exhibited enhanced mechanical stability, and maintained their selectivity over at least 4 weeks. For membranes of low ionophore concentration, the polymer affected the sensor selectivity noticeably at polymer concentrations exceeding 15%. Also, the membrane resistance increased quite strongly at high polymer concentrations, which cannot be explained by the Mackie-Meares obstruction model. The selectivities and resistances depend on the polymer concentration because of a functional group associated with Teflon AF2400, with a concentration of one functional group per 854 monomer units of the polymer. In the fluorous environment of these membranes, this functional group binds to Na+, K+, Ca2+, and the unprotonated ionophore with binding constants of 10(3.5), 10(1.8), 10(6.8), and 10(4.4) M(-1), respectively. Potentiometric and spectroscopic evidence indicates that these functional groups are COOH groups formed by the hydrolysis of carboxylic acid fluoride (COF) groups originally present in Teflon AF2400. The use of higher ionophore concentrations removes the undesirable effect of these COOH groups almost completely. Alternatively, the C(=O)F groups can be eliminated chemically, or they can be used to readily introduce new functionalities.

Stripping Analysis of Nanomolar Perchlorate in Drinking Water with a Voltammetric Ion-Selective Electrode Based on Thin-Layer Liquid Membrane

A highly sensitive analytical method is required for the assessment of nanomolar perchlorate contamination in drinking water as an emerging environmental problem. We developed the novel approach based on a voltammetric ion-selective electrode to enable the electrochemical detection of "redox-inactive" perchlorate at a nanomolar level without its electrolysis. The perchlorate-selective electrode is based on the submicrometer-thick plasticized poly(vinyl chloride) membrane spin-coated on the poly(3-octylthiophene)-modified gold electrode. The liquid membrane serves as the first thin-layer cell for ion-transfer stripping voltammetry to give low detection limits of 0.2-0.5 nM perchlorate in deionized water, commercial bottled water, and tap water under a rotating electrode configuration. The detection limits are not only much lower than the action limit (approximately 246 nM) set by the U.S. Environmental Protection Agency but also are comparable to the detection limits of the most sensitive analytical methods for detecting perchlorate, that is, ion chromatography coupled with a suppressed conductivity detector (0.55 nM) or electrospray ionization mass spectrometry (0.20-0.25 nM). The mass transfer of perchlorate in the thin-layer liquid membrane and aqueous sample as well as its transfer at the interface between the two phases were studied experimentally and theoretically to achieve the low detection limits. The advantages of ion-transfer stripping voltammetry with a thin-layer liquid membrane against traditional ion-selective potentiometry are demonstrated in terms of a detection limit, a response time, and selectivity.

Quantitative chemical analysis of electrolytes in aqueous solutions exploiting the Donnan dialysis process

Chemical analysis of electrolytes in aqueous solutions is performed with a dialyzer consisting of two selective membranes: a cation and an anion-exchange membrane. The dialyzer actually functions like a galvanic cell when dialysis is carried out. The current that appears in the cell is measured. Since the dialysis process is caused by the concentration gradient, the current measured also depends on the concentration gradient. For proper conditions, it becomes possible to determine the concentration. The method may compete in some aspects with ion-selective potentiometry.