Neutral Ionophores Research Articles

Ni(II)-selective ion sensors of salen type Schiff base chelates

The two nickel chelates of Schiff bases, N-(2-hydroxybenzyl)- N′-(2-hydroxybenzylidene)ethylenediamine Ni(II) ( I) and N-(2-hydroxybenzylidene)- N′-(2-picolyl)ethylenediamine Ni(II) ( II), have been synthesized and explored as a neutral ionophores for preparing polyvinyl chloride based membrane sensors selective to Nickel(II). The addition of sodium tetraphenylborate and various plasticizers, viz., DOS, TEHP, DEP and CN has been found to substantially improve the performance of the sensors. The best performance was obtained with the sensor having membrane of chelate ( II) with composition (w/w) chelate (1%):PVC (33%):CN (65.5%):NaTPB (0.5%). This sensor exhibits Nernstian response in the concentration range 3.2 × 10 −6 to 5.0 × 10 −2 M Ni(II), performs satisfactorily over wide pH range of (2.2–5.9) with a fast response time (∼10 s). The sensor was also found to work satisfactorily in partially non-aqueous media up to 25% (v/v) content of acetone, methanol or ethanol and could be used over a period of 4 months. The response of the sensor was highly selective to Ni 2+ over a large number of cations and it could therefore be used for Ni 2+ estimation in the presence of a number of interfering ions. The sensor could be used successfully for the estimation of nickel at trace level in biological and environmental samples.

A comparative study of Pb 2+ selective sensors based on derivatized tetrapyrazole and calix[4]arene receptors

Two neutral ionophores, 2,12-dimethyl-7,17-diphenyltetrapyrazole ( I) and 5,11-dibromo-25,27-dipropoxycalix[4]arene ( II) have been explored for preparing PVC based membrane sensors selective to Pb 2+. The addition of sodium tetraphenylborate and various plasticizers viz. DOS, TEHP, DBP, DOP and TBP has been found to substantially improve the performance (working concentration range, slope and response time) of the sensors. The best performance was obtained with the sensor having a membrane of composition (w/w) of ( I) (1%):PVC (33%):TBP (65%):NaTPB (1%). The sensor exhibits Nernstian response in the concentration range 2.5 × 10 −6 to 5.0 × 10 −2 M Pb 2+, performs satisfactorily over wide pH range (1.6–6.0) with a fast response time (∼10 s). The sensor was found to work satisfactorily in partially non-aqueous media up to 25% (v/v) content of acetone, methanol or ethanol and could be used over a period of 5 months. Potentiometric selectivity coefficients as determined by match potential method (MPM) indicate excellent selectivity for Pb 2+ ions. The sensors could be used successfully in the estimation of lead in Eveready battery waste and also as an indicator electrode in potentiometric titration.

New diamino compound as neutral ionophore for highly selective and sensitive PVC membrane electrode for Be 2+ ion

The complexation of synthesized diamine 2,6-bis[2-( o-aminophenoxy)methyl]-4-bromo-1-methoxybenzene with different ions was studied conductometrically. The best interaction was observed between the diamine and Be 2+ ion and the formation constant of the resulting complex was evaluated. The suitability of the diamine compound as a beryllium ion carrier in a PVC membrane electrode for potentiometric determination of Be 2+ ion was investigated. The prepared electrode, with optimum composition, exhibits a Nernstian response to Be 2+ ion over a wide concentration range from 3.0 × 10 −6 to 7.0 × 10 −2 M and a very low detection limit of 2.0 × 10 −6 M. It has an appropriate response time and suitable reproducibility, and can be used for a period of at least 1 month without any measurable divergence. The potentiometric response is independent of the pH of the test solution in the range of 4.0–7.0. The proposed sensor reveals good selectivity toward Be 2+ ion with respect to many alkali, alkaline earth, transition and heavy metal ions. It was applied to the determination of beryllium in tap water samples and also samples containing interfering ions.

Novel potentiometric copper (II) selective membrane sensors based on cyclic tetrapeptide derivatives as neutral ionophores

Two novel membrane sensors sensitive and reasonably selective for Cu 2+ ions are described. These are based on the use of newly synthesized cyclic tetrapeptide derivatives as neutral ionophores and sodium tetraphenylborate (NaTPB) as an anionic excluder in plasticized PVC membranes. The sensors exhibit fast and stable near-Nernstian response over the concentration range 1.0 × 10 −6 mol l −1 to 1.0 × 10 −2 mol l −1 Cu 2+ with a cationic slope of 30.2–25.9 mV per decade at pH 4.5–7 with a lower detection limit of 0.05–0.13 μg ml −1. Effects of plasticizers, lipophilic salts and various foreign common ions are tested. The sensors display long life-span, long term stability, high reproducibility, and short response time. Selectivity of both sensors is significantly high for Cu 2+ over Fe 3+, Al 3+, Zn 2+, Cd 2+, Hg 2+, Ni 2+, Co 2+, Mn 2+, alkaline earth and alkali metal ions. The sensors are used for direct measurement of copper content in different rocks and industrial wastewater samples from electroplating factories. The results agree fairly well with data obtained using atomic absorption spectrometry.

PVC Membrane Potentiometric Sensor Based on 5-Pyridino-2,8-dithia[9](2,9)-1,10-phenanthroline- phane for Selective Determination of Neodymium(III)

Spectrofluorometric studies on the binding properties of 5-pyridino-2,8-dithia[9](2,9)-1,10-phenanthrolinephane (L) toward La3+, Sm3+, Gd3+, Yb3+, and Nd3+ in methanol solution revealed the occurrence of both 1:1 and 2:1 (ligand/metal) complexation with a stability order of Nd3+ > Yb3+ > Gd3+ > Sm3+ > La3+. Consequently, L was used as a suitable neutral ionophore for the preparation of a novel polymeric membrane-selective electrode for Nd3+ ion. The electrode exhibited a Nernstian response over a wide concentration range (1.0 x 10(-6)-1.0 x 10(-2) M) with a low limit of detection of 7.9 x 10(-7) M. The electrode possesses a fast response time of <5 s and can be used for at least 9 weeks without observing any considerable deviation. The proposed electrode revealed a very good selectivity for Nd3+ over a wide variety of alkali, alkaline earth, transition, and heavy metal ions, including members of the lanthanide family other than Nd3+. The potentiometric response of the electrode is independent of the pH of test solution in the pH range 4.0-6.5. The proposed electrode was successfully applied to the recovery of Nd3+ ion from tap water samples and, also, as an indicator electrode, in potentiometric titration of neodymium(III) ions.

Urea-functionalized calix[4]arenes as carriers for carbonate-selective electrodes

A new PVC membrane electrode for CO 3 2− anion based on urea-functionalized calix[4]arenes (I–IV) as neutral ionophores is prepared. Of the various membranes prepared, the membrane based on bis-urea calix[4]arene I exhibits a linear stable response over a concentration range (5.0 × 10 −4 to 1.0 × 10 −1) with a slope of −29.2 mV per decade and a detection limit of 1.2 × 10 −4 M, and the best selectivity for CO 3 2− anion [ K T C O 2 J pot = 1.9 × 10 − 2 ( sa l − ) and 2.1 × 10 − 2 ( I − ) ] over salicylate and iodide.

Magnesium-selective test strip

A selective test strip based on an ion-exchange mechanism to determine magnesium is described. This optical and reversible test strip, made on a transparent polyester sheet, has a circular polymeric film of plasticised PVC that contains all of the reagents necessary to produce a response to magnesium, namely, a cation-selective neutral ionophore, 2-amino- N, N′-diheptyl- N, N′-dimethyl-butanediamide, a chromoionophore, N, N-diethyl-5-(octadecanoylimino)-5 H-benzo[ a]phenoxazine-9-amine, and potassium tetrakis (4-chlorophenyl)borate (TCPB) as a lipophilic salt, which is evaluated by absorbance measurement at 655 nm in a standard photometer. The experimental variables that influence test strip response, especially in terms of selectivity and response time, have been studied. The test strip responded linearly to magnesium between 0.009 and 160 mM in activities. The reproducibility intermembrane at a medium level of the range was 8.0%, as R.S.D., of log a M g 2 + , and 5.9% as R.S.D. intramembrane. The procedure was applied to the determination of magnesium in different types of waters (tap, well and mineral) validating the results against a reference procedure. This proposed method is quick, inexpensive, selective and sensitive and uses only conventional instrumentation.

Influences of hard donor on cation selectivities closing to soft selenium donor in tweezer‐like calix[4]arene receptors

AbstractThree novel 25,27‐dihydroxy‐26,28‐bis(3‐benzylselenopropoxy)‐5,11,17,23‐tetra‐tert‐butylcdix[4]‐arene (2), 25,27‐dihydroxy‐26,28‐bis[3‐(2‐hydroxyethylseleno)propoxy]‐5,11,17,23‐tetra‐tert‐butyl‐calix[4]arene (3) and 25,27‐dihydroxy‐26,28‐bis(3‐propylselenopropoxy)‐5,11,17,23‐tetra‐tert‐butyI‐calix[4]arene (4) were synthesized for the comparison of their ion‐selectivity in ion‐selective electrodes (ISE). X‐ray structure of the CH/π complex of 4·CH2Cl2 was elucidated. ISEs based on 2‐4 as neutral ionophores were prepared, and their selectivity coefficients for Ag+ (log K) were investigated against some main group metal ions and transition metal ones using the fixed interference method (FZM). These ISEs showed excellent Ag' selectivity over most of the interfering cations examined. It is evident that the stronger Hg2+ interference may not be produced while hard donors (hydroxy) are close to the soft selenium donors.

Investigation of ion-selective electrodes with neutral ionophores and ionic sites by EIS. I. Theory

Models of an ion selective electrode involving an ionophore and mobile sites in a membrane are proposed. The first model, called the phase boundary potential model, supposed thermodynamic equilibrium; it allows the concentrations of the various species to be calculated. Then, a kinetic model, which takes into account the ionic transfer at the membrane|solution interfaces, was derived. The impedance of the membrane was calculated. It shows that a membrane with nernstian behavior shows only one capacitive loop in the impedance diagram, which is related to the conductivity and dielectric properties of the material of the membrane. Non-nernstian behavior is related to slow ionic transfer at the membrane|solution interfaces or/and transport limitation of the species in the membrane. Finite rate constants of the ionic transfer lead to a capacitive loop in the middle frequency range, whereas finite rate transport leads to a diffusional impedance in the low frequency range.

Investigation of ion-selective electrodes with neutral ionophores and ionic sites by EIS. II. Application to K + detection

The impedance of an ion-selective electrode (ISE) to potassium with valinomycin as the ionophore and KBΦ 4 as the ionic sites was measured. The membrane was made of PVC with DNP as a plasticizer. The influence of the content of the plasticizer and the membrane thickness was investigated. The concentrations of the ionophore and the ionic sites were changed to modify the response on the ISE. Finally, the selectivity was tested in terms of impedance. All impedance experiments were correlated to the potentiometric curves plotted under the same experimental conditions. The measured impedances were compared to the model proposed in the previous paper (paper I). A good agreement was found.

Potentiometric quasi-array employing calixarene derivatives for the high-throughput similarity/diversity screening of beta-adrenergic and beta-blocking chiral drugs by HPLC.

Performance of potentiometric quasi-array detection system consisted with the seven poly (vinyl chloride) (PVC) based liquid membrane electrodes in the cation-exchange HPLC using acetonitrile--40 mM phosphoric acid (15 : 85, v/v, pH* 2.35) for assessing of molecular similarity/diversity in a mini-library of beta-adrenergic and beta-blocking chiral drugs was presented. Macrocyclic compounds differing in stability of their conformers as well as in a size, steric hindrance and polarity of its internal cavities, comprising a series of five calix[6]arene derivatives completed with one modified calix[4]resorcinarene, were used as neutral ionophores to compose mentioned set of PVC-based electrodes. The output potentiometric responses were registered in the linear supernerstian range of calibration graph of each electrode, i.e. for a constant injected concentration 2.0 x 10(-4) M of investigated drugs, which is related to the amount frequently used at in vitro studies on pharmacological effects of these drugs. The impact of symmetry oriented supramolecular interactions on the responses of developed electrodes were characterised with proposed series of the highly significant quantitative structure-potentiometric response relationships (QSPRRs) combining both three-dimensional (3D) molecular descriptors of analysed drugs as well as lipophilicity and volume polarizability of calixarene-type ionophores. The principal components analysis (PCA) and unweighted hierarchical clustering analysis (HCA) were used as the pattern recognition techniques into collected potentiometric database for extraction of the useful information on the molecular and pharmacological similarity/diversity of analysed drugs, thus a high-throughput and consistent identification of therapeutically relevant agonists of beta2- and beta3-adrenoceptors and antagonists of beta1-adrenoceptor was especially achieved. This evidence supports also a hypothesis formulated by results of homology modelling on the subtle significance of an unrecognised supramolecular insertion processes of the chiral drug molecule into the flexible hydrophobic pocket(s) formed by seven helical transmembrane moving domains of beta-adrenoceptors on their final activation, sequestration, down-regulation or blockade.

Irreversible optical test strip for mercury determination based on neutral ionophore

A test strip for the determination of mercury in aqueous solution has been developed. It has a circular sensing zone containing all the reagents necessary to produce a selective response to mercury and formed by plasticised PVC incorporating the cation-selective neutral ionophore 1,4,7,10-tetraazacyclododecane, the chromoionophore 9-dimethylamino-5-[4-(15-butyl-1,13-dioxo-2,14-dioxanonadecyl)phenylimino]benzo[a]phenoxazine and tetrabutylammonium tetraphenylborate as lipophilic salt. The measurement principle is based on an ion-exchange mechanism. When the sensor is introduced for a period of time depending on the mercury content into a water sample at a pH of 4.7, there is a colour change from blue to red, making it possible to use absorbance at 670 nm as the analytical signal. All experimental variables that influence the test strip response, especially in terms of selectivity and response time, were studied. The sensor responded linearly to mercury concentration in the range 0.3 and 5.1 μM with a reproducibility in mid-calibration of 1.6% relative standard deviation (R.S.D.) for 60 min agitation. Similarly, it responded linearly to concentrations in the range 7.9–108 μM with a mid-range R.S.D. of 1.8% (for 5 min without agitation). The procedure was applied to the determination of mercury in different types of waters (tap, mineral and spring), validating the results against a reference procedure.

Irreversible optical test strip for mercury determination based on neutral ionophore

A test strip for the determination of mercury in aqueous solution has been developed. It has a circular sensing zone containing all the reagents necessary to produce a selective response to mercury and formed by plasticised PVC incorporating the cation-selective neutral ionophore 1,4,7,10-tetraazacyclododecane, the chromoionophore 9-dimethylamino-5-[4-(15-butyl-1,13-dioxo-2,14-dioxanonadecyl)phenylimino]benzo[a]phenoxazine and tetrabutylammonium tetraphenylborate as lipophilic salt. The measurement principle is based on an ion-exchange mechanism. When the sensor is introduced for a period of time depending on the mercury content into a water sample at a pH of 4.7, there is a colour change from blue to red, making it possible to use absorbance at 670 nm as the analytical signal. All experimental variables that influence the test strip response, especially in terms of selectivity and response time, were studied. The sensor responded linearly to mercury concentration in the range 0.3 and 5.1 μM with a reproducibility in mid-calibration of 1.6% relative standard deviation (R.S.D.) for 60 min agitation. Similarly, it responded linearly to concentrations in the range 7.9–108 μM with a mid-range R.S.D. of 1.8% (for 5 min without agitation). The procedure was applied to the determination of mercury in different types of waters (tap, mineral and spring), validating the results against a reference procedure.

Microfabrication and characterization of an ion-selective microelectrode array platform

The design and the fabrication of an ion-selective electrode array platform aimed at in vitro intracellular recording are presented. The platform is composed of two parts: (i) a glass chip with microchannels whose bottom part is patterned with a platinum layer and (ii) a silicon chip in which an array of 50 μm long silicon nitride micropipettes with an inner diameter of 5 μm are structured. The 24 micropipettes are individually filled with a Ca 2+ selective membrane, based on the neutral ionophore ETH 129. Preliminary tests in Ca 2+ buffered solutions have shown a linear range from 10 −6 to 0.1 M Ca 2+ with a sensitivity of 27 mV/decade.

Optical determination of ionophore diffusion coefficients in plasticized poly(vinyl chloride) sensing films

The knowledge of accurate diffusion coefficients of electrically neutral ionophores in solvent polymeric membranes is important in view of understanding and optimizing important sensor characteristics of ion-selective electrodes (ISEs) and their corresponding optical sensors. A spectroscopic imaging technique is introduced here to determine the diffusion coefficient of the chromoionophore ( N, N-diethyl-5-(octadecanoylimino)-5 H-benzo[a]phenoxazine-9-amine, ETH 5294) in solvent polymeric membranes with different types of plasticizers and varying polymer–plasticizer ratio. This method is based on following the changes in the absorbance profiles of the chromoionophore as a function of space and time. The desired membrane composition is solvent cast onto a glass slide and placed under a microscope objective. The membrane is then exposed to light from a mercury arc lamp which photobleaches the dye in a circular area, providing an interface from which the time rate of absorbance change is studied. Spectral images are acquired over fixed time intervals with a microscope equipped with a charge-coupled device (CCD) camera providing 0.41 μm nominal resolution. Two plasticizers, ortho-nitrophenyl octyl ether ( o-NPOE) and bis(2-ethylhexyl) sebacate (DOS), are examined in poly(vinyl chloride) (PVC) by varying the ratio of polymer to plasticizer content and measuring the diffusion coefficient of the chromoionophore. Corresponding membrane compositions containing 10 wt.% of an inert lipophilic salt (ETH 500) are also examined. Near linear relationships between the logarithmic diffusion coefficients and the PVC content are observed that obey the following relationships: log D=−6.17 –0.0459 wt.% PVC (for PVC–DOS), log D=−6.46 –0.0468 wt.% PVC (for PVC–DOS–ETH 500), log D=−5.89 –0.0508 wt.% PVC (for PVC–NPOE), log D=−6.22 –0.0473 wt.% PVC (for PVC–NPOE–ETH 500).

Novel Dicyanoargentate Polymeric Membrane Sensors for Selective Determination of Cyanide Ions

AbstractThe construction and general performance characteristics of three novel potentiometric PVC membrane sensors responsive to dicyanoargentate anion are described. The sensors are based on the use of magnesium(II)‐ and iron(II)‐phthalocyanines as neutral ionophores and iron(II)‐bathophenanthroline dicyanoargentate ion‐pair complex as an ion exchanger in plasticized PVC matrices. These sensors exhibit fast, stable and near‐Nernstian response (54–59 mV/decade) for the singly charged dicyanoargentate anion over the concentration range 1×10−2–5.8×10−6 M. Potentiometric responses of sensors based on metal phthalocyanines and iron(II)‐bathophenanthroline are stable over the pH ranges 5–7 and 5–12, respectively. The selectivity of the sensors are fairly good over most common anions. Use of the sensors for potentiometric determination of microgram quantities of cyanide ion after conversion into dicyanoargentate anions shows an average recovery of 99.5% and a mean standard deviation of ±0.5%. Determination of cyanide ions in some exhausted electroplating bath samples gives results that compare favourably well with data obtained using the solid‐state cyanide electrode.

New Macrocyclic Diamides as Neutral Ionophores for Highly Selective and Sensitive PVC‐Membrane Electrodes for Be2+ Ion

AbstractFive recently synthesized macrocyclic diamides were investigated to characterize their ability as beryllium ion carriers in potentiometric PVC‐membrane electrodes. The electrodes based on 1,15‐diaza‐3,4;12,13‐dibenzo‐5,8,11‐trioxabicyclo[13,2,2] heptadecane‐2,14‐dione exhibited a Nernstian response for Be2+ ion over wide concentration ranges (from 3.0×10−6 to 3.0×10−2 M for polymeric membrane electrode, PME, and from 5.0×10−7 to 2.0×10−2 M for coated glassy carbon electrode, CGCE) and very low detection limits (2.0 ×10−6 M for PME and 4.0×10−7 M for (CGCE). The electrodes possess low resistances, fast responses, satisfactory reproducibilities and, most importantly, good selectivities relative to a variety of other common cations. The potentiometric response of the electrodes is independent of pH of test solution in the pH range of 4.0–7.5. The proposed sensors were used to determine beryllium ion in water samples.

Hydroxy-thioxanthones as suitable neutral ionophores for the preparation of PVC-membrane potentiometric sensors for Al(III) ion.

The complexation of five recently synthesized hydroxy-thioxanthone derivatives with Al3+ ion was studied in a methanol solution spectrophotometrically, and the stepwise formation constants of the resulting 1:1 and 2:1 (ligand-to-metal) complexes were evaluated. The suitability of the thioxanthone derivatives as neutral ionophores for the preparation of a new Al3+ ion-selective PVC-membrane electrode was investigated, and 1-hydroxy-3-methyl-thiocanthone was selected as the best compound for this purpose. The prepared electrode exhibits a Nernstian response for Al3+ ions over a wide concentration range (2.0 x 10(-2) to 2.0 x 10(-6) M), with a limit of detection of 1.0 x 10(-6) M. It has a very fast response time of about 5 s and can be used for at least 3 months without any considerable divergence in the potentials. The proposed membrane sensor revealed very good selectivities for Al3+ over a wide variety of other metal ions, and could be used at a working pH range of 3.4 - 5.0. It was used as an indicator electrode in potentiometric titration of aluminum ions with EDTA, and in the determination of Al3+ in different real samples.

Nitrate-selective electrodes based on meso-tetrakis[(2-arylphenylurea)-phenyl]porphyrins as neutral lipophilic ionophores

Polymeric-membrane electrodes for NO 3 − anion based on (α,α,α,α)-5,10,15,20-tetrakis [2-(4-methylphenylurea)phenyl]porphyrin I and similar urea-functionalized porphyrins II– IV as neutral ionophores were prepared. The effects of polymeric-membrane composition and test solution pH were tested. The electrodes revealed good selectivity coefficients for NO 3 − over a wide variety of other anions, and the values of eight anions were measured. Of the various electrodes prepared, the electrode based on urea-functionalized porphyrin I exhibits a linear stable response over a wide concentration range (1.0×10 −5 to 1.0×10 −1) with a slope of −57.4 mV per decade, a detection limit of log[NO 3 −]=−5.72, and a selectivity coefficient for nitrate against perchlorate anion ( log K NO 3 −,j pot =−1.81 ).

PVC membrane and coated graphite potentiometric sensors based on Et4todit for selective determination of samarium(III).

Solution studies on the binding properties of 4,5,6,7-tetrathiocino[1,2-b:3,4-b']diimidazolyl-1,3,8,10-tetraethyl-2,9-dithione (Et(4)todit) toward a number of cationic species including some lanthanide ions revealed the occurrence of a selective 1:1 complexation of the ligand with Sm(3+) ion. Consequently, Et(4)todit was used as a suitable neutral ionophore for the preparation of novel polymeric membrane (PME) and coated graphite (CGE) Sm(3+)-selective electrodes. The electrodes exhibit a Nernstian behavior for Sm(3+) ions over wide concentration ranges (1.0 x 10(-5)-1.0 x 10(-1) M for PME and 1.0 x 10(-7)-1.0 x 10(-1) M for CGE) and very low limits of detection (8.0 x 10(-6) M for PME and 1.6 x 10(-8) M for CGE). The proposed potentiometric sensors manifest advantages of relatively fast response, and, most importantly, good selectivities relative to wide variety of other cations, including other lanthanide ions. The selectivity behavior of the proposed Sm(3+)-selective electrodes revealed a great improvement compared to the best previously reported electrode for samarium(III) ion. The potentiometric responses of the electrodes are independent of the pH of the test solution in the pH range 4.0-6.5. The electrodes were successfully applied to the recovery of Sm(3+) ion from tap water samples and also, as an indicator electrode, in potentiometric titration of samarium(III) ions.