Neutral Ionophores Research Articles

Novel Ionophores for Barium‐Selective Electrodes: Synthesis and Analytical Characterization

AbstractA novel way of synthesis is developed for the Ba2+ selective neutral Ionophore 2a: 2,2′‐[1,2‐phenylenebis(oxyethane‐2,1‐diyloxy)]bis(N‐benzyl‐N‐phenylacetamide) and its methyl (2b), buthyl (2c), and hexyl (2d) derivatives. Ba2+ selective electrodes based on Ionophores 2a–d are compared with those with commonly used Ionophore 1: N,N,N′,N′‐tetracyclohexyl‐oxybis(o‐phenyleneoxy) diacetamide. It is shown that Ionophores 2a–d, particularly 2b, are superior for measurements of Ba2+ in the presence of Ca2+, and in acidic solutions. Segmented sandwich membrane studies suggest formation of complexes IL22+ for Ba2+, Ca2+ and Mg2+ ions with Ionophore 2b, while H+ ions apparently form complexes H2L2+. The values of the complex formation constants are consistent with the selectivity coefficients.

Gallium(III) selective sensors based on 2-amino-3-(α-N-phenylmethyl-2′-amino-1′,4′-naphthoquinonyl)-1,4 naphthoquinones in poly (vinyl chloride)

Synthesis and application of 2-amino-3-(α-N-phenylmethyl-2′-amino-1′,4′-naphthoquinonyl)-1,4 naphthoquinone ( S) as a neutral ionophore for the determination of gallium(III) in PVC-based membrane sensors has been described. The sensor based on membrane composition (w/w, mg%); 5.0 ( S):30.0 (PVC):5.0 (KTpClPB):60.0 ( o-NPOE) is the best and showed a working range of 2.3 × 10 −7 to 1.0 × 10 −2 M with detection limit of 1.2 × 10 −7 M. It can tolerate non-aqueous media up to 15% with a slope of 19.7 mV decade −1 of activity. The sensor has been used to assess the Ga(III) concentration in different natural samples (peach and tomato leaves, coal-fly-ash and river sediments). It can be used for 2.5 months without any distortion in results, after which, leaching of ionophore was observed from the membrane phase. The proposed sensor has shown a good dynamic response time of 11 s.

Can Temperature Be Used To Tune the Selectivity of Membrane Ion-Selective Electrodes?

The selectivity coefficients, KIJpot, of ion-selective electrodes (ISEs) have been fundamentally related to thermodynamic parameters, but yet, the effect of temperature on KIJpot has not been studied. We describe a new approach to fine-tune the selectivity of ISEs based on the effect of temperature on selectivity coefficients. This effect was quantified for ion exchangers as well as neutral carrier ionophores. Potassium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate was used as an ion exchanger in a poly(vinyl chloride) membrane. The corresponding electrode showed an inverse relationship between log KNa+,K+pot and temperature. Additionally, sodium-selective electrodes using monensin, monensin methyl ester (MME), and monensin decyl ester (MDE) were evaluated as models of electrodes based on neutral carriers. The electrode based on monensin showed an enhancement in the selectivity for sodium over potassium by half an order of magnitude as the temperature increased from 20 to 50 degrees C, while the electrodes based on MME or MDE showed a very small change in selectivity. This can be explained in light of changes in the formation constants between the ions and ionophores with temperature. The theory of the effect of temperature on selectivity for both ion exchangers and neutral carrier ionophores is also discussed.

Comparative study on 2-amino-1,4-naphthoquinone derived ligands as indium (III) selective PVC-based sensors

The three different ligands (Q 2 to Q 4) based on 2-amino-1,4-naphthoquinone (Q 1), have been synthesized and explored as neutral ionophores for preparing polyvinyl chloride-based membrane sensors selective to indium (III). The addition of potassium tetrakis(4-chlorophenyl) borate and various plasticizers, viz., o-NPOE, DBP, DBBP, DOP and CN has been found to substantially improve the performance of the sensors. The best performance was obtained with the sensor no. 16 having membrane of ligand (Q 2) with composition (%, w/w) ionophore Q 2 (3.0%):PVC (30.0%): o-NPOE (63.0%):KTpClPB (4.0%). This sensor exhibits Nernstian response with slope 19.8 mV/decade of activity in the concentration range 2.5 × 10 −7 to 1.0 × 10 −2 M indium (III), performs satisfactorily over wide pH range of (2.5–7.5) with a fast response time (10 s). The sensor was also found to work satisfactorily in partially non-aqueous media up to 20% (v/v) content of acetonitrile, ethanol and methanol. The proposed sensor can be used over a period of 3.5 months without significant drift in potentials. The quantitative application of sensor was also evaluated by comparative analysis of artificially made sea water with AAS.

Determination of terbium in phosphate rock by Tb 3+-selective fluorimetric optode based on dansyl derivative as a neutral fluorogenic ionophore

For the first time a highly sensitive and selective fluorimetric optode membrane was prepared for determination of trace amounts of Tb(III) ions in phosphate rock samples. The Tb(III) sensing system was constructed by incorporating 5-(dimethylamino)-N′-(2-hydroxy-1-naphthoyl) naphthalene-1-sulfonohydrazine (L) as a neutral Tb(III)-selective fluoroionophore, in the plasticized PVC membrane containing sodium tetraphenyl borate as a liphophilic anionic additive. The response of the optode is based on the strong fluorescence quenching of L by Tb 3+ ions. At a pH value of 5.0, the optode displays a wide concentration range of 1.0 × 10 −7 to 1.0 × 10 −2 M, with a relatively fast response time of less than 45 s. In addition, to high stability and reproducibility, the sensor shows a unique selectivity towards Tb 3+ ion with respect to common cations. The optode was applied successfully to the trace determination of terbium ion in binary mixture and water samples and the determination of Tb 3+ in phosphate rock samples.

N, N′ -Bis(3-methyl-1-phenyl-4-benzylidine-5-pyrazolone)propylenediamine Schiff base as a neutral carrier for silver (I) ion-selective electrodes

New highly selective silver (I) electrodes were prepared by incorporating N, N′-bis(3-methyl-1-phenyl-4-benzylidine-5-pyrazolone)propylenediamine ( I2) as a neutral ionophore into plasticized PVC membranes. The best response characteristics were obtained using the composition— I2:KTpClPB:PVC:DBP in the percentage ratio of 4:1.5:60:120 (w:w). The electrodes exhibit a linear response with a near Nernstian slope of 59.3 mV/decade within the silver ion concentration range of 10 −6–0.1 mol L −1, with a working pH range (4–10). The electrodes possessed a fast response time of 30 s for low concentration (10 −6 mol L −1) and 5 s for higher concentration (10 −5–0.1 mol L −1). The electrodes showed excellent selectivity towards Ag + ion over a wide range of alkali, alkaline earth, and transition metals ions. The electrodes displayed a very good selectivity for silver ion against the serious interferents Hg 2+ and Cu 2+ ions, which is a valuable property of these electrodes. The high selectivity arises from the strong complexation of I2 with Ag + compared with other ions as determined by the sandwich membrane method. Density Functional Theory calculations performed using the Gaussian 03 program indicate a tetradentate coordination of the metal ion by I2. Calculated binding energies for different metal ions also support high selectivity for silver (I) ion. These electrodes were successfully used in the potentiometric titration of halides with silver ion and in the determination of silver in radiology films.

Potentiometric polymeric membrane electrodes for mercury detection using calixarene ionophores

It is here established that potentiometric polymeric membrane electrodes based on electrically neutral ionophores are a useful analytical tool for the detection of heavy metal ions from environmental and industrial waste water. PVC based membrane containing p-tert-butyl-calix[4]arenethioether derivative as active material along with sodiumtetraphenylborate (NaTPB) as solvent mediator and dibutylphthalate as a plasticizer in the ratio 45:9:460:310 (w/w%) (I:NaTPB:DBP:PVC) exhibits good properties with a Nernstian response of 29.50+/-1.0 mV per decade of activity and a working concentration range of 7.2 x 10(-8)-1.0 x 10(-1) M. The electrode gave more stable potential readings when used around pH 2.5-6.8 and exhibits fast response time of 14 s. The sensors were found to work satisfactorily in partially non-aqueous media up to 40% (v/v) content of acetone, methanol or ethanol and could be used over a period of 7-9 months. Excellent selectivity for Hg(2+) ions is indicated by match potential method and fixed interference method. The sensors could be used successfully in the estimation of mercury in different sample.

A comparative study of four 20-membered N 2S 4-crown ethers as ionophores for polymeric membrane silver selective electrodes

Four 20-membered N 2S 4-monoazathiacrown ethers have been synthesized and explored as neutral ionophores for Ag +-selective electrodes. Potentiometric responses reveal that the flexibility of the ligands has great effect on the selectivity and sensitivity to Ag + ions. The electrode based on ionophore 9,10,20,25-tetrahydro-5 H,12 H-tribenzo[b,n,r][1,7,10,16,4,13]tetrathiadiaza cycloicosine 6,13-(7 H,14 H)-dione ( C) with 2-nitrophenyl octyl ether ( o-NPOE) as solvent in a poly(vinyl chloride) (PVC) membrane matrix shows a measuring range of 1.0 × 10 −6 to 1.0 × 10 −3 mol/L with a Nernstian slope of 54.9 ± 0.3 mV/decade. This electrode has high selectivity for Ag + with negligible interference from many other cations and can be used in a wide pH range of 3.6–9.2.

New potentiometric sensors based on two competitive recognition sites for determining tetracycline residues using flow-through system

New potentiometric membrane sensors for tetracycline (TC) are described based on the use of a newly designed molecularly imprinted polymer (MIP) material based on 2-vinylpyridine as a functional monomer, AmION (I) [Calix-4-arene tetraacetic acid ester] as neutral ionophore in plasticized PVC membranes. Effects of lipophilic salts and various foreign common ions are tested. The sensors exhibit significantly high sensitivity, stability and selectivity for TC+ ions over many common ions and are successfully used for determining TC+ ions in spiked biological fluid samples under static and hydrodynamic mode of operations.

Photocurable pH-sensitive membrane for ion-selective field effect transistors

H(+)-ion sensitive ISFETs with photocured polyurethane-based polymer membranes with three different neutral carrier ionophores and four different plasticizers have been studied in 0.05 M TRIS-HCl solutions and in background solutions containing 140 mM of Na(+) ions. The optimised membrane composition showing the best selectivity contains 2.2-2.5 wt.% of the ionophore (tridodecylamine), 36-41 wt.% of a plasticizer, and only 10 mol% of a lipophilic salt KTClPhB. The optimal ionophore/lipophilic salt ratio obtained in this work differs significantly from theoretically recommended for pH-sensitive ion-selective membranes. It is assumed that this is due to the participation of the ionophore (tertiary amine) and lipophilic additives (tetrachlorophenylborate anion) in additional photochemical reactions occurring during irradiation of the membrane matrix. Sensors with the optimised membrane composition showed sufficient sensor selectivity in front of sodium ions for clinical and biomedical applications and the lifetime of more than 3 months.

Novel flow-through bulk optode for spectrophotometric determination of lithium in pharmaceuticals and saliva

Abstract A new flow-through spectrophotometric bulk optode for the determination of lithium is reported. The optode membrane incorporates a lipophilic pH indicator (chromoionophore XIV), a lipophilic neutral ionophore (lithium ionophore VIII) and potassium tetrakis[3,5-bis(trifluoromethyl) phenyl] borate (ionic additive) as active constituents in a plasticized poly(vinyl) chloride membrane, entrapped in a cellulosic support. The composition of the membrane was tested using two different plasticizers. The optode was incorporated in a flow-injection system optimized for the determination of lithium. The analytical performance of the optode was evaluated, obtaining a linear concentration range of two decades of concentration (1 × 10−4 to 1 × 10−2 M), a limit of detection of 1.4 × 10−4 M, a fast sample throughput (25–4 samples h−1) and good reproducibility and selectivity. The sensor was seen to exhibit a fully reversible response. The proposed FI method is applied to the determination of lithium in pharmaceuticals and human saliva with satisfactory results.

Samarium(III)-PVC-Membrane Sensor Based on Ethoxy-1-ethoxycarbonyl-1,2-dihydroquinoline

2-Ethoxy-1-ethoxycarbonyl-1,2-dihydroquinoline (EED) was found to be a suitable neutral ionophore for the preparation of a highly selective samarium (Sm)(III) membrane sensor. Poly vinylchloride (PVC)–based membranes of EED with sodium tetraphenyl borate (NaTPB) as an anionic additive and dibutylphthalate (DBP), nitrobenzene (NB), and acetophenone (AP) as plasticizing solvent mediators were prepared and investigated as Sm(III) sensors. The sensor exhibited a Nernstian response over a concentration range of 1.0 × 10−6 to 1.0 × 10−2 M, with a detection limit of 5.0 × 10−7 M. The best performance was achieved with a membrane composition of 30% PVC, 66% dibutyl phthalate (DBP), 2% EED, and 2% sodium tetraphenyl borate (NaTPB). It has a very short response time, in the whole concentration range (∼10s), and can be used for at least 10 weeks. The proposed electrode shows a very good selectivity toward Sm(III) ions over a wide variety of cations, including alkali, alkaline earth, transition-metal, and heavy-metal ions. The sensor was applied to the determination of Sm ions in binary mixtures.

Generalized selectivity description for polymeric ion-selective electrodes based on the phase boundary potential model

A generalized description of the response behavior of potentiometric polymer membrane ion-selective electrodes is presented on the basis of ion-exchange equilibrium considerations at the sample–membrane interface. This paper includes and extends on previously reported theoretical advances in a more compact yet more comprehensive form. Specifically, the phase boundary potential model is used to derive the origin of the Nernstian response behavior in a single expression, which is valid for a membrane containing any charge type and complex stoichiometry of ionophore and ion-exchanger. This forms the basis for a generalized expression of the selectivity coefficient, which may be used for the selectivity optimization of ion-selective membranes containing electrically charged and neutral ionophores of any desired stoichiometry. It is shown to reduce to expressions published previously for specialized cases, and may be effectively applied to problems relevant in modern potentiometry. The treatment is extended to mixed ion solutions, offering a comprehensive yet formally compact derivation of the response behavior of ion-selective electrodes to a mixture of ions of any desired charge. It is compared to predictions by the less accurate Nicolsky–Eisenman equation. The influence of ion fluxes or any form of electrochemical excitation is not considered here, but may be readily incorporated if an ion-exchange equilibrium at the interface may be assumed in these cases.

Batch and hydrodynamic monitoring of vitamin C using novel periodate selective sensors based on a newly synthesized Ni(II)-Schiff bases complexes as a neutral receptors

A highly selective membrane electrodes based on a two newly synthesized nickel (II) Schiff bases, [NiL 1] and [NiL 2] where L 1 and L 2 are N,N/bis(salicylaldehyde)4,5-dimethyl-1,2-phenylenediamine (H 2L 1) and N,N/bis(salicylaldehyde)4,5-dichloro-1,2-phenylenediamine (H 2L 2) were used as a neutral carrier ionophores for static and hydrodynamic potentiometric mode of operations for the determination of periodate. Under static mode of operation, the sensors displayed a near-Nernstian slope of −66.1 ± 0.8 and −59.9 ± 1.1 mV decade −1 of activity and detection limits to 5.2 × 10 −6 and 7.3 × 10 −6 mol L −1 for the sensors based on [NiL 1] and [NiL 2], respectively. Under hydrodynamic mode of operation (FIA), the slope of the calibration plot, limit of detection, and working linear range were −71.1 mVdecade −1 of activity, 7.3 × 10 −6 and 1.0 × 10 −5 to 1.0 × 10 −3 mol L −1, respectively. The response time of the sensors in whole concentration ranges was very short (<10 s). The response of the sensors was independent on the pH range of 3–8. A tubular version was further developed and coupled to a flow injection system for ascorbic acid (AA) determination in beverages and pharmaceutical preparations. This approach was achieved by selecting a 50-cm reactor and an overall flow of 3 mL min −1, and injecting volume 100 μL of AA standards in a 1.0 × 10 −4 mol L −1 IO 4 − solution. Under these conditions, a linearity range of 2–13 μg mL −1, with a slope of 4.97 mV (mg/L) −1 ( r 2 = 0.9995), detection limit 0.9 mg L −1 and a reproducibility of ±1.1 mV ( n = 5) was recorded. This simple and inexpensive flow injection analysis manifold, with a good potentiometric detector, enabled the analysis of ∼50 samples h −1 without requiring pretreatment procedures. An average recovery of 98.8% and a mean standard deviation of 1.3% were obtained.

Investigation of Potential Distribution and the Influence of Ion Complexation on Diffusion Potentials at Aqueous−Aqueous Boundaries within a Dual-Stream Microfluidic Structure

The occurrence of reactions at boundaries between adjacent miscible but unmixed aqueous streams coflowing in a microfluidic channel structure has been studied by simulation of the diffusion potentials that develop between the two coflowing aqueous electrolyte streams and by measurement of the effects of aqueous ion complexation on diffusion potentials. The microfluidic structure consisted of a Y-shaped microchannel with off-chip electrodes immersed in electrolyte reservoirs connected by capillaries to the Y-microchannel. The time-dependent, one-dimensional Nernst-Planck equation employing the electroneutrality condition was solved numerically to calculate the diffusion potentials established at the boundary between the two coflowing aqueous streams. Under the experimental conditions (channel length and width, flow rate) employed, it was shown that the use of the Henderson equation was appropriate. It was also shown that the cross-channel diffusion potential remained constant from the entrance of the channel to the exit. The influence of cation complexation by a neutral ionophore was investigated by experimentally measured diffusion potentials. It was found that potassium complexation by the cyclic polyether 18-crown-6 altered the experimental diffusion potential, whereas the interaction of sodium or lithium cations with the ionophore did not perturb the diffusion potential. The results are consistent with the literature data for aqueous-phase complexation of these cations by this ionophore. The results of these investigations demonstrate that relatively simple diffusion potential measurements between coflowing streams in microchannels may be used as a basis for study of ion complexation reactions occurring at boundaries between miscible fluids.

New Copper(II) Ion-Selective Membrane Electrode Based on Erythromycin Ethyl Succinate as a Neutral Ionophore

The potentiometric response characteristics of a new copper(II) ion-selective PVC membrane electrode based on erythromycin ethyl succinate (EES) as ionophore were investigated. The electrode exhibited a Nernstian response to Cu2+ ions over the activity range of 1.5 × 10−2 to 2.0 × 10−6 mol L−1 with a limit of detection of 6.3 × 10−7 mol L−1. Stable potentials were obtained in the pH range of 5.5–6.5. The potentiometric selectivity coefficients were calculated by using fixed interference method and revealed no important interferences except for Ag+. This electrode was successfully applied as an indicator electrode in determination of copper ions in real water samples.

A Fast Response Strontium Ion‐Selective Electrode Prepared by Sol‐Gel Membrane Technique

AbstractA sol‐gel electrode, based on 6‐(4‐nitrophenyl)‐2‐phenyl‐4,4‐dipropyl‐3,5‐diaza‐bicyclo [3,1,0] hex‐2‐ene (NPDBH) as a neutral ionophore, was successfully developed for the detection of Sr2+ in aqueous solutions. Theoretical calculations confirmed NPDBH selectivity toward strontium in comparison with some other metal ions. The electrode responds to Sr2+ ion with a sensitivity of 29.1±0.4 mV/decade over the range 8.0×10−7–1.0×10−1 M. Selectivity coefficients determined by matched potential method (MPM) indicate high selectivity for strontium ions. The electrode has a fast response time of 11 s and a working pH range of 3.0–10.0. The sol‐gel electrode shows detection limit of 7.5×10−8 M.

Poly(3,4-ethylenedioxythiophene) (PEDOT) doped with carbon nanotubes as ion-to-electron transducer in polymer membrane-based potassium ion-selective electrodes

Negatively charged multi-walled carbon nanotubes (MWCNTs) were used as dopants in the electrochemical synthesis of the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT). The resulting electroactive film, PEDOT(CNT), was used as ion-to-electron transducer (solid contact) in potassium ion-selective electrodes (K +-ISEs) based on plasticized PVC membrane containing valinomycin as neutral ionophore. Potentiometric measurements were carried out to study the analytical performance of solid-contact K +-ISEs, the influence of dissolved O 2 and CO 2 on the potential of the electrodes, and the formation of the interfacial aqueous film. The prepared electrodes were also characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronopotentiometry. The experimental results showed that PEDOT(CNT) has the capability to function as solid contact in fabrication of K +-ISEs. These electrodes, based on PEDOT(CNT) as ion-to-electron transducer, showed high sensitivity and selectivity to K + ion which can be related to the plasticized PVC-based ion-selective membrane containing valinomycin. The stability of the electrode potential, however, was found to depend on the conducting substrate used for deposition of the PEDOT(CNT) film. Results from the CV and EIS revealed that the PEDOT(CNT) contact exhibits high redox capacitance that is favorable for a solid contact.

Comparative studies of neodymium (III)-selective PVC membrane sensors

Sensors based on two neutral ionophores, N,N′-bis((1H-pyrrol-2-yl)methylene)cyclohexane-1,2-diamine ( L 1 ) and 3,3′-(cyclohexane-1,2-diylbis(azan-1-yl-1-ylidene)bis(methan-1-yl-1-ylidene)bis(5-hydroxymethyl)pyridine-2-ol) ( L 2 ) are described for quantification of neodymium (III). Effect of various plasticizers; 2-nitrophenyloctylether ( o-NPOE), dibutyl butylphosphonate (DBBP), tri-n-butyl phosphates (TBP), dioctylpthalate (DOP) and chloronapthalen (CN) and anion excluder, sodiumtetraphenylborate (NaTPB) has been studied. The membrane composition of PVC: o-NPOE:ionophore ( L 1 ):NaTPB (w/w; mg) of 150:300:5:5 exhibited best performance. The sensor with ionophore ( L 1 ) exhibits significantly enhanced selectivity towards neodymium (III) in the concentration range 5.0 × 10 −7 to 1.0 × 10 −2 M with a detection limit of 1.0 × 10 −7 M and a Nernstian compliance (19.8 ± 0.3 mV decade −1 of activity) within pH range 4.0–8.0. The response time of sensor was found as 10 s. The influence of the membrane composition and possible interfering ions has also been investigated on the response properties of the electrode. The fast and stable response, good reproducibility and long-term stability of the sensor are observed. The sensor has been found to work satisfactorily in partially non-aqueous media up to 20% (v/v) content of methanol, ethanol or acetonitrile and could be used for a period of 3 months. The selectivity coefficients determined by using fixed interference method (FIM) indicate high selectivity for neodymium. The proposed electrode shows fairly good discrimination of neodymium (III) from other cations. The application of prepared sensor has been demonstrated in the determination of neodymium (III) in spiked water samples.

Comparative evaluation of Dy(III) selective poly(vinyl) chloride based membrane electrodes of macrocyclic tetraimine Schiff's bases

Three different derivatives of macrocyclic tetraimine Schiff's base have been synthesized and explored as a neutral ionophores for preparing poly(vinyl chloride) based membrane sensors selective to Dy 3+. The addition of sodium tetraphenyl borate and various plasticizers, viz., o-NPOE, DBP, DBBP, DOP and CN has been found to substantially improve the performance of the sensors. The best performance was obtained with the sensor no. 1 having membrane of Schiff's base (SL-1) with composition (w/w) SL-1 (4.5%): PVC (30.5%): o-NPOE (59.5%): NaTPB (5.5%). This sensor exhibits Nernstian response with slope 19.4 mV/decade of activity in the concentration range of 10 −8 to 1.0 × 10 −2 M Dy 3+, performs satisfactorily over wide pH range of (2.8–7.2) with a fast response time (10 s). The sensor was also found to work satisfactorily in partially non-aqueous media up to 20% (v/v) content of acetonitrile, methanol or ethanol. The proposed sensor can be used over a period of 1.5 months without significant drift in potentials. The sensor has been also utilized for the determination of Dy 3+ level in different soil samples.