Lipophilic Ions Research Articles

Using Polyvinyl Chloride and Screen-Printed Electrodes for the Determination of Levofloxacin in the Presence of Its Main Photo-Degradants in River Water: A Comparative Study

The application of membrane sensors for the detection and quantification of pharmaceutical environmental contaminants has become a significant goal in recent years. Due to the widespread application of levofloxacin hemihydrate (LEVO) in medicine, its occurrence in the environment, especially in surface water bodies like rivers, is quite likely. Extended exposure of river water to sunlight and the photo-degradability of LEVO may facilitate its photo-degradation. To measure LEVO in the presence of its principal photo-degradants, two sensitive and selective membrane electrodes were designed. A polyvinyl chloride electrode (PVCE) and a screen-printed electrode (SPE) were constructed for the selective analysis of the investigated drug. Phosphomolybdic acid was used to prepare a lipophilic ion pair with the studied drug. All test parameters were optimized to achieve the best electrochemical performance. The electrodes demonstrated a linear range from 1 × 10−6 M to 1 × 10−2 M. The PVCE and SPE demonstrated slopes of 55.80 ± 0.70 mV/decade and 56.90 ± 0.50 mV/decade, respectively. The aforementioned sensors demonstrated satisfactory performance within a pH range of 3.0 to 5.0. The fabricated sensors were successfully utilized to accurately quantify LEVO in the presence of its primary photo-degradants. The membranes were effectively utilized to measure LEVO in river water samples without requiring pre-treatment processes.

Parallel Amperometric and Potentiometric Multianalyte Detection in a Microfluidic System

The adoption of microfluidic technologies in electrochemical biosensor development has enabled quantitative biomarker monitoring that use significantly lower volumes of reagents and samples, miniaturized electrodes, and inexpensive fabrication techniques, while presenting opportunities for multianalyte detection. We describe the fabrication of amperometric and potentiometric biosensors on a multichannel, platinum screen-printed electrode (SPE) and demonstrate their operation in parallel on a microfluidic multianalyte electrochemical sensor array (µMESA) platform.Working electrodes (WEs) of an SPE were were modified with either enzymes or ion selective membranes (ISMs) for amperometric or potentiometric measurements respectively. Oxidase enzymes were dissolved in an osmium (II) bis(2,2'-bipyridine)chloride-poly(vinylimidazole-allylamine) redox polymer and immobilized on four WEs. The use of this osmium-based electron transfer mediator has been previously reported to lower the oxidation potential of analytes and to improve overall sensor performance. The remaining four WEs were modified by electrodeposition of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), an intrinsically conductive polymer. Solid contact ISMs were prepared by combining ionophores, lipophilic ion exchangers, and a fluorosilicone polymer, and drop casting the mixtures on PEDOT:PSS-coated WEs. Plasticizer-free ISMs improve sensor lifetime by lowering the glass transition temperature and eliminating leaching of plasticizers from the ISM. By utilizing these strategies, we fabricated amperometric sensors for glucose and lactate, and potentiometric sensors for K+ and Ca2+ ions. Glucose is a primary substrate for energy metabolism while lactate is a major metabolite and signaling molecule. K+ ions maintain cell membrane physiology and homeostasis whereas Ca2+ ions serve as messengers during muscle activity and neurotransmission.Sensor characteristics like sensitivity, selectivity, linear range, and operational longevity for each biosensor were assessed using chronoamperometry or chronopotentiometry techniques on a potentiostat/potentiometer instrument. The results indicate that the sensor fabrication strategies described, in combination with our µMESA platform, can be used to measure changes in metabolite concentrations under laminar flow. Ultimately, this versatile technology may provide novel insights into complex physiological and pathological processes in biological systems.

New Trends in Asymmetric Phase Transfer Catalysis

AbstractPhase Transfer Catalysis (PTC) is a powerful tool to perform reactions in a practical fashion, both in laboratory and industrial scale. Significant cost savings and major process improvements can be achieved in reactions performed under PTC conditions. In the last few years remarkable results in stereoselective reactions were achieved using chiral, non‐racemic quaternary ammonium salts. Moreover, the use of bulky, chiral phosphate anions paired with achiral cations to generate lipophilic ion pairs allowed to design new avenues for the stereoselective construction of important building blocks. Hydrogen bond interactions were also shown to provide new pathways for asymmetric nucleophilic substitutions using insoluble reagents under PTC conditions. This Review will focus on recent advances in developing practical synthetic routes to construct molecules in a stereoselective fashion under PTC conditions.

Response Mechanism of Polymeric Liquid Junction-Free Reference Electrodes Based on Organic Electrolytes.

To achieve a transition from conventional liquid-junction reference electrodes (LJF REs) to their all-solid-state alternatives, organic electrolytes are often introduced into the polymeric electrode membranes. In this article, we implement a theoretical approach to the explanation and quantification of the boundary potential stabilization phenomenon for the electrodes modified with organic electrolytes (Q+B-). For the first time, stabilization of the phase boundary potential due to the partition of lipophilic ions of the Q+B- electrolyte between the polymeric and aqueous phases is numerically simulated to predict the LJF electrodes behavior. The impact of the hydrophilic electrolyte on the potential stabilization is demonstrated both numerically and experimentally. The developed model predicted that the small additions of a traditional ion-exchanger enhance performance of the Q+B--based reference electrodes. For some specific cases, the optimal concentrations of Q+B- and ion-exchanger in the polymeric phase are suggested to provide stable electrode potential in a broad range of aqueous electrolyte concentrations. In addition, the efficiency of the stabilization was shown to be dependent on the overall Q+B- load in the polymeric membrane rather than on the closeness of the partition coefficients of the Q+ and B- ions; and on the volume of the aqueous phase. The model results are verified experimentally with poly(vinyl chloride) membranes containing ion-exchanger or hydrophilic electrolyte and Q+B- in various proportions. A good agreement between the measured electrode response and the theoretical results is observed in a broad range of solution concentrations. In particular, the cationic function of membranes containing KTpClPB is suppressed, and the electrodes begin to behave as REs starting from 50-60 mol. % of ETH500 electrolyte added to the membrane, relative to the total amount of salt.

Exploitation of multi-walled carbon nanotubes/Cu(ii)-metal organic framework based glassy carbon electrode for the determination of orphenadrine citrate.

Metal organic frameworks (MOFs), with structural tunability, high metal content and large surface area have recently attracted the attention of researchers in the field of electrochemistry. In this work, an unprecedented use of multi-walled carbon nanotubes (MWCNTs)/copper-based metal-organic framework (Cu-BTC MOF) composite as an ion-to-electron transducer in a potentiometric sensor is proposed for the determination of orphenadrine citrate. A comparative study was conducted between three proposed glassy carbon electrodes, Cu-MOF, (MWCNTs) and MWCNTs/Cu-MOF composite based sensors, where Cu-MOF, MWCNTs and their composite were utilized as the ion-to-electron transducers. The sensors were developed for accurate and precise determination of orphenadrine citrate in pharmaceutical dosage form, spiked real human plasma and artificial cerebrospinal fluid (ACSF). The sensors employed β-cyclodextrin as a recognition element with the aid of potassium tetrakis(4-chlorophenyl)borate (KTpCIPB) as a lipophilic ion exchanger. The sensors that were assessed based on the guidelines recommended by IUPAC and demonstrated a linear response within the concentration range of 10-7 M to 10-3 M, 10-6 M to 10-2 M and 10-8 M to 10-2 M for Cu-MOF, MWCNTs and MWCNTs/Cu-MOF composite based sensors, respectively. MWCNTs/Cu-MOF composite based sensor showed superior performance over other sensors regarding lower limit of detection (LOD), wider linearity range and faster response. The sensors demonstrated their potential as effective options for the analysis of orphenadrine citrate in quality control laboratories and in different healthcare activities.

Ionic co-aggregates (ICAs) based oral drug delivery: Solubilization and permeability improvement.

Due to the overwhelming percentage of poorly water-soluble drugs, pharmaceutical industry is in urgent need of efficient approaches for solubilization and permeability improvement. Salts consisting of lipophilic fatty acid anions and hydrophilic choline cations are found to be surface active and able to form ionic co-aggregates (ICAs) in water. Choline oleate-based ICAs significantly enhance oral absorption of paclitaxel (PTX) as compared with cremophor EL-based micelles (MCs). Aggregation-caused quenching probes enable tracking of intact ICAs in in vivo transport and cellular interaction. Prolonged intestinal retention of ICAs than MCs implies stronger solubilizing capability in vivo. Ex vivo imaging of major organs and intestinal tracts suggests transepithelial transport of intact ICAs. Cellular studies support the enhanced absorption of PTX and transmembrane transport of intact ICAs. In conclusion, ICAs, consisting of lipophilic ions and hydrophilic counter-ions, are of great potential in delivery of poorly water-soluble drugs by enhancing solubility and permeability.

A case of pseudohyperchloraemia caused by sodium nitrate ingestion

Emergency department presentations of sodium nitrate poisoning are increasing in frequency. Point-of-care blood gas analysis is useful for identifying methaemoglobinaemia and other abnormalities in such patients. Topically applied nitrate is known to positively interfere with chloride measurement in both point-of-care instruments and automated analysers of the clinical chemistry laboratory. In this article, the authors describe a case of pseudohyperchloraemia caused by sodium nitrate, which was consumed orally for the purpose of suicide. Consistent with the established pattern of interference, the ABL800 (Radiometer Medical, Brønshøj Copenhagen) blood gas analyser produced spuriously high chloride results, whilst the Alinity (Abbott Diagnostics, Abbot Park, Illinois) automated analyser resulted in chloride measurements comparable to those of inductively coupled mass spectrometry (ICP-MS). Both instruments, measure chloride with ion-selective electrodes (ISEs). The ABL800 (Radiometer) uses a membrane electrode, which is vulnerable to permeation by lipophilic nitrate ions, whereas the Alinity (Abbott) employs a silver chloride redox electrode system that is resistant to precipitation of silver nitrate due to its relatively high solubility. These mechanistic differences likely explain why nitrate interferes with some point-of-care devices but does not appear to affect the results of automated analysers.

Polyvinyl Chloride Modified Carbon Paste Electrodes for Sensitive Determination of Levofloxacin Drug in Serum, Urine, and Pharmaceutical Formulations.

Levofloxacin (LF) is a medically important antibiotic drug that is used to treat a variety of bacterial infections. In this study, three highly sensitive and selective carbon paste electrodes (CPEs) were fabricated for potentiometric determination of the LF drug: (i) CPEs filled with carbon paste (referred to as CPE); (ii) CPE coated (drop-casted) with ion-selective PVC membrane (referred to as C-CPE); (iii) CPE filled with carbon paste modified with a plasticizer (PVC/cyclohexanone) (referenced as P-CPE). The CPE was formulated from graphite (Gr, 44.0%) and reduced graphene oxide (rGO, 3.0%) as the carbon source, tricresyl phosphate (TCP, 47.0%) as the plasticizer; sodium tetrakis[3,5-bis(trifluoromethyl)phenyl] borate (St-TFPMB, 1.0%) as the ion exchanger; and levofloxacinium-tetraphenylborate (LF-TPB, 5.0%) as the lipophilic ion pair. It showed a sub-Nernstian slope of 49.3 mV decade−1 within the LF concentration range 1.0 × 10−2 M to 1.0 × 10−5 M, with a detection limit of 1.0 × 10−5 M. The PVC coated electrode (C-CPE) showed improved sensitivity (in terms of slope, equal to 50.2 mV decade−1) compared to CPEs. After the incorporation of PVC paste on the modified CPE (P-CPE), the sensitivity increased at 53.5 mV decade−1, indicating such improvement. The selectivity coefficient () against different interfering species (Na+, K+, NH4+, Ca2+, Al3+, Fe3+, Glycine, Glucose, Maltose, Lactose) were significantly improved by one to three orders of magnitudes in the case of C-CPE and P-CPE, compared to CPEs. The modification with the PVC membrane coating significantly improved the response time and solubility of the LF-TPB within the electrode matrix and increased the lifetime. The constructed sensors were successfully applied for LF determination in pharmaceutical preparation (Levoxin® 500 mg), spiked urine, and serum samples with high accuracy and precision.

Deploying hydrogen bond donor/acceptor on arylethynyl scaffold II: Urea based tripodal ionophores for polymeric membrane nitrate selective electrodes

Along the line for developing ionophores by deploying hydrogen bond donor/acceptor on arylethynyl acaffold, two tripodal urea receptors were used as ionophores for the first time to fabricate polymeric membrane nitrate-selective electrodes. Replacing the hydrogens with fluorine atoms in the arylethynyl core facilitates the selectivity for nitrate over halides, originating from the additional anion–π interactions electron between nitrate and deficient fluorinated core. By optimizing membrane composition such as plasticizers and lipophilic additives, the proposed ISEs showed Nernstian response to nitrate with superior selectivity to both lipophilic ions and halides. Although the formation constants of anions-ionophore complex in membrane phase did not correlate well with the selectivity pattern of the ISEs, these data were consistent with that in solvent such as binary DMSO/CHCl3. The proposed ISEs could work in wide pH range solutions with short response time, good reversibility and reproducibility, which led to the success of determination of nitrate in real mineral water, tap water, as well as river water samples.

Lipophilic ion aromaticity is not important for permeability across lipid membranes

To clarify the contribution of charge delocalization in a lipophilic ion to the efficacy of its permeation through a lipid membrane, we compared the behavior of alkyl derivatives of triphenylphosphonium, tricyclohexylphosphonium and trihexylphosphonium both in natural and artificial membranes. Exploring accumulation of the lipophilic cations in response to inside-negative membrane potential generation in mitochondria by using an ion-selective electrode revealed similar mitochondrial uptake of butyltricyclohexylphosphonium (C4TCHP) and butyltriphenylphosphonium (C4TPP). Fluorescence correlation spectroscopy also demonstrated similar membrane potential-dependent accumulation of fluorescein derivatives of tricyclohexyldecylphosphonium and decyltriphenylphosphonium in mitochondria. The rate constant of lipophilic cation translocation across the bilayer lipid membrane (BLM), measured by the current relaxation method, moderately increased in the following sequence: trihexyltetradecylphosphonium ([P6,6,6,14]) < triphenyltetradecylphosphonium (C14TPP) < tricyclohexyldodecylphosphonium (C12TCHP). In line with these results, measurements of the BLM stationary conductance indicated that membrane permeability for C4TCHP is 2.5 times higher than that for C4TPP. Values of the difference in the free energy of ion solvation in water and octane calculated using the density functional theory and the polarizable continuum solvent model were similar for methyltriphenylphosphonium, tricyclohexylmethylphosphonium and trihexylmethylphosphonium. Our results prove that both cyclic and aromatic moieties are not necessary for lipophilic ions to effectively permeate through lipid membranes.

A Breakthrough Application of a Cross-Linked Polystyrene Anion-Exchange Membrane for a Hydrogencarbonate Ion-Selective Electrode.

Polystyrene cross-linked with divinylbenzene and functionalized by a quaternary ammonium cation anion site is used as the membrane of a hydrogencarbonate (i.e., bicarbonate) ion-selective electrode. The polystyrene matrix membrane improves the selectivity towards interfering lipophilic ions in comparison to previously described polyvinyl chloride membranes. The reason for this behaviour is sought in coupled ion-exchange and pore-diffusion processes in the membrane and the resulting kinetic discrimination of interfering ions. The electrode is successfully used for determination of bicarbonates in mineral drinking waters. The simplex method is employed to refine the analytical outcome.

3D spongy-like Au film for highly stable solid contact potentiometric ion selective electrode: application to drug analysis

Potentiometric ion selective electrodes with simple design and high potential stability are required for in-line process, clinical and quality control analysis. The objective of this work is to develop a high-surface-area Au nanostructure solid-contact (SC) platform for high stable ion selective electrode for drug analysis. Memantine, a pharmaceutical compound prescribed for Alzheimer’s disease, with challenging measurable analytical characteristics, was selected as a model for this purpose. Internal solid-contact with a high surface area was prepared by direct electrochemical deposition of Au-nanostructures onto a Pt electrode (500 µm diameter and 3 mm long). The proposed design combines the small size with the high surface area that is necessary for stable potential response. Cyclic voltammetry, impedance electrochemical spectroscopy and chronopotentiometry were used to evaluate electrochemical properties of the Au film. The Au-nanostructure SC electrode was coated with a membrane cocktail containing a lipophilic ion exchanger. The electrode exhibited a Nernstian response (58.5 ± 1 mV/decade) to memantine over a wide concentration range (1 × 10−5–1 × 10−2 M). The electrode showed high potential stability (0.03 µV/s), wide pH working range (3.0–8.0) and high selectivity to memantine $$\left( {\log k_{i,j}^{pot} \le - 2.38} \right)$$ . The electrode was applied for direct determination of memantine in pharmaceutical dosage form, human urine and surface water with high accuracy (± 2%) and precision (RSD ≤ 1.5%).

Effect of methyl and halogen substituents on the transmembrane movement of lipophilic ions.

Penetrating cations are widely used for the design of bioactive mitochondria-targeted compounds. The introduction of various substituents into the phenyl rings of dodecyltriphenylphosphonium and the measurement of the flip-flop of the synthesized cations by the current relaxation method revealed that methyl groups accelerated significantly the cation penetration through the lipid membrane, depending on the number of groups introduced. However, halogenation slowed down the penetration of the analogues. This result is strictly opposite to the flip-flop acceleration observed for halogenated tetraphenylborate anions. Density functional theory and the polarizable continuum solvent model were used to calculate the solvation energies of methyltriphenylphosphonium and methyltriphenylborate analogues. A good agreement was demonstrated between the difference in the free energy of ion solvation in water and octane and the absolute value of the central free energy barrier estimated from experimental data. Our results reveal that increasing the size of the lipophilic ion can lead to both acceleration and deceleration of the transmembrane flip-flop rate depending on the substituent and sign of the ion. This finding also emphasizes the different nature of ion-water interactions for structurally similar substituted hydrophobic anions and cations.

Ion Transport Mechanisms in Liquid-Liquid Interface.

Interfacial liquid-liquid ion transport is of crucial importance to biotechnology and industrial separation processes including nuclear elements and rare earths. A water-in-oil microemulsion is formulated here with density and dimensions amenable to atomistic molecular dynamics simulation, facilitating convergent theoretical and experimental approaches to elucidate interfacial ion transport mechanisms. Lutetium(III) cations are transported from the 5 nm diameter water pools into the surrounding oil using an extractant (a lipophilic ligand). Changes in ion coordination sphere and interactions between the interfacial components are studied using a combination of synchrotron X-ray scattering, spectroscopy, and atomistic molecular dynamics simulations. Contrary to existing hypotheses, our model system shows no evidence of interfacial extractant monolayers, but rather ions are exchanged through water channels that penetrate the surfactant monolayer and connect to the oil-based extractant. Our results highlight the dynamic nature of the oil-water interface and show that lipophilic ion shuttles need not form flat monolayer structures to facilitate ion transport across the liquid-liquid interface.

Disassembly Control of Saccharide-Based Amphiphiles Driven by Electrostatic Repulsion.

According to the design of disassembly using electrostatic repulsion, novel amphiphiles consisting of a lipophilic ion part and a hydrophilic saccharide part were synthesized via the facile copper-catalyzed click reaction, and their molecular assemblies in water and chloroform were studied. The amphiphiles exhibited a molecular orientation opposite to that of the conventional amphiphiles in each case. ζ Potential measurements indicated that the lipophilic ion part is exposed outside in chloroform. The size of a solvophobic part in the amphiphiles dominates the size of an assembling structure; that is, in water, these amphiphiles tethering different lengths of the saccharide part exhibited almost identical assembling size, whereas in chloroform, the size depends on the length of the saccharide part in the amphiphiles.

Thermoresponsivity of polymer solution derived from a self-attractive urea unit and a self-repulsive lipophilic ion unit

Proper design of a self-attractive unit and a self-repulsive ion unit on a polymer chain successfully generated thermoresponsivity in non-aqueous solvents.

Lipid Rescue Reverses the Bupivacaine-induced Block of the Fast Na+ Current (INa) in Cardiomyocytes of the Rat Left Ventricle

Cardiovascular resuscitation upon intoxication with lipophilic ion channel-blocking agents has proven most difficult. Recently, favorable results have been reported when lipid rescue therapy is performed, i.e., the infusion of a triglyceride-rich lipid emulsion during resuscitation. However, the mechanism of action is poorly understood. The authors investigate the effects of a clinically used lipid emulsion (Lipovenös® MCT 20%; Fresenius Kabi AG, Bad Homburg, Germany) on the block of the fast Na current (INa) induced by the lipophilic local anesthetic bupivacaine in adult rat left ventricular myocytes by using the whole cell patch clamp technique. Bupivacaine at 10 µm decreased INa by 54% (-19.3 ± 1.9 pApF vs. -42.3 ± 4.3 pApF; n = 17; P < 0.001; VPip = -40 mV, 1 Hz). Addition of 10% lipid emulsion in the presence of bupivacaine produced a 37% increase in INa (-26.4 ± 2.8 pApF; n = 17; P < 0.001 vs. bupivacaine alone). To test whether these results could be explained by a reduction in the free bupivacaine concentration by the lipid (lipid-sink effect), the authors removed the lipid phase from the bupivacaine-lipid mixture by ultracentrifugation. Also, the resulting water phase led to an increase in INa (+19%; n = 17; P < 0.001 vs. bupivacaine), demonstrating that part of the bupivacaine had been removed during ultracentrifugation. The substantially less lipophilic mepivacaine (40 µm) reduced INa by 27% (n = 24; P < 0.001). The mepivacaine-lipid mixture caused a significant increase in INa (+17%; n = 24; P < 0.001). For mepivacaine, only a small lipid-sink effect could be demonstrated (+8%; n = 23; P < 0.01), reflecting its poor lipid solubility. The authors demonstrate lipid rescue on the single-cell level and provide evidence for a lipid-sink mechanism.

Effect of General Anesthetics and Alcohols on Prestin (SLC26A5) Function

Prestin is a membrane protein essential to the electromotility of outer-hair cells (OHC) in the cochlea. This protein with piezoelectric properties has shown sensitivity to changes in cell membrane physical properties. The presence of molecules which impact the lateral pressure or the fluidity of the membrane -such as cholesterol, NSAIDs or lipophilic ions- can alter the electrophysiological properties of prestin as well as the electromotility. In an OHC, the nonlinear capacitance (NLC) and the electromotility are both conferred by prestin and coupled. This allows monitoring the NLC as a surrogate measure of prestin's function.Here we describe the impact of general anesthetics and alcohols on prestin, and aim to use this protein as a model system for studying membrane-protein interaction through changes in the NLC. We tested the effect on prestin of alcohols with various C-chains (C2 to C10) and some general anesthetics (GA: propofol, isoflurane, halothane, chloroform, etomidate and xylazine). All the alcohols tested trigger a dose-dependent shift in the characteristic voltage at half-maximal charge transfer (V1/2), with the sensitivity increasing as the alcohols' carbon-chain is longer. The direction of the shift changes with concentration, the lower concentration cause a negative shift while higher concentrations shift V1/2 closer to 0mV. These shifts are correlated with changes in the linear capacitance of the cell. All of the GA we tested caused a dose-dependent increase in charge density at sub-millimolar concentrations as well as a shift of V1/2 toward hyperpolarized voltages. The sensitivity of prestin to these molecules seems to follow the Meyer/Overton correlation.The shift in the NLC as well as the increase in charge density can modify the function of the OHC at resting potential and alter cochlear amplification.

Electric Field Driven Extraction of Inorganic Anions Across a Polymer Inclusion Membrane

AbstractThe potential use of plasticized cellulose acetate membranes for electric field driven extraction and preconcentration of inorganic anions was studied. The extraction of highly lipophilic ions such as perchlorate is possible by employing a membrane without any ion carrier, while anions of low lipophilicity, such as phosphate, require a carrier. Best extraction efficiency could be obtained for a membrane of 20 µm thickness and an applied voltage of 200 V. In a flow‐through arrangement the preconcentration factor was inversely dependent on the flow rate but constant for different concentrations. The extraction of perchlorate down to 2 nM was demonstrated.

Potentiometric Sensors with Ion-Exchange Donnan Exclusion Membranes

Potentiometric sensors that exhibit a non-Hofmeister selectivity sequence are normally designed by selective chemical recognition elements in the membrane. In other situations, when used as detectors in separation science, for example, membranes that respond equally to most ions are preferred. With so-called liquid membranes, a low selectivity is difficult to accomplish since these membranes are intrinsically responsive to lipophilic species. Instead, the high solubility of sample lipids in an ionophore-free sensing matrix results in a deterioration of the response. We explore here potentiometric sensors on the basis of ion-exchange membranes commonly used in fuel cell applications and electrodialysis, which have so far not found their way into the field of ion-selective electrodes. These membranes act as Donnan exclusion membranes as the ions are not stripped of their hydration shell as they interact with the membrane. Because of this, lipophilic ions are no longer preferred over hydrophilic ones, making them promising candidates for the detection of abundant ions in the presence of lipophilic ones or as detectors in separation science. Two types of cation-exchanger membranes and one anion-exchange membrane were characterized, and potentiometric measuring ranges were found to be Nernstian over a wide range down to about 10 μM concentrations. Depending on the specific membrane, lipophilic ions gave equal response to hydrophilic ones or were even somewhat discriminated. The medium and long-term stability and reproducibility of the electrode signals were found to be promising when evaluated in synthetic and whole blood samples.