Salicylate-Selective PVC Membrane Electrodes Based on Tribenzyltin(IV) Phenolates as Neutral Carriers

ABSTRACT

A series of tribenzyltin(IV) phenolates were synthesized and used as anion ionophores for PVC membrane electrodes; these novel electrodes exhibit a linear response towards salicylate and an anti-Hofmeister selectivity pattern with high specificity for salicylate over many common anions. The results show that the behavior of the electrodes is considerably influenced by the structures of the carriers and the experimental conditions. Electrodes based on tribenzyltin(IV) p-nitrophenolate possess the best potentiometnc response characteristics and show a linear log[Sal^?] vs. EMF response over the concentration range 0.1–3.98×10^?6 mol.L^?1 in phosphate buffer solutions of pH 5.38 with a detection limit of 2.51×10^?6 mol.L^?1 and a slope of -57.05 mV per decade. The response mechanism was also investigated by use of a.c. impedance and anion transport across liquid membranes. The electrodes were applied to the determination of salicylate in urine samples with satisfactory results.     

FTIR-ATR-spectroscopic analysis of Bis-Crown ether based PVC-membranes

Summary To get more information on the phase boundary and bulk membrane processes, the short and long time behaviour of potassium selective solvent polymeric membranes was studied. In parallel with the measurement of the dynamic response of model membranes, in situ spectroscopic measurements applying the Attenuated Total Reflection (ATR) technique in the infrared region, were carried out in solutions containing anions of different lipophilicity (Cl^– and SCN^–). Thin membranes (thinner than the penetration depth of IR beam) coated on the germanium reflection element by the dipping technique show no time dependence of the SCN bands in contact with KSCN solution of different concentrations, while the diffusion process of species can be monitored in thick membranes as it was shown in a time resolved study. The extremely short response times of ionophore based solvent polymeric membranes (determined under appropriate experimental conditions in this work) imply that the fundamental potential determining step of the overall response of this type of electrodes is a phase boundary process. Thus the slow inner membrane diffusion process followed by IR spectroscopy on the molecular level may affect only the long-term membrane behaviour.

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FTIR-ATR-spektroskopische Analyse von Bis-Kronenether-PVC-MembranenIII. Spektroskopische und elektrochemische in situ-Methoden zur Untersuchung von OberflÄchen- und Bulk-Membran-Prozessen

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Part II: see [4]

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Dedicated to Prof. Dr. W. Fresenius on the occasion of his 75th birthday     

Hydrophobic ionic liquids in plasticized membranes of ion-selective eletctrodes

Ionic liquids with substituted imidazole, pyridine, and pyrrolidine cations and hydrophobic anions are studied as ionophores of PVC membranes of ion-selective electrodes plasticized with 2-nitrophenyloctyl ether. These membranes show a response to hydrophobic organic cations. In solutions of cationic surfactants, the slope of the electrode function is close to the theoretical one and the limit of detection does not exceed n × 10⁻⁶ M. Ion-selective electrodes for anions are developed using a trioctylmethylammonium salicylate ionic liquid. The electrode on its basis shows a stable potentiometric response to the salicylate anion in a wide range of concentrations and is characterized by good selectivity in the presence of foreign anions.     

Application of flow-injection potentiometric system for determination of total concentration of aliphatic carboxylic acids

In this work, flow-injection system with potentiometric detection was tested for determination of total carboxylic acid concentration. Detection part of the examined system consists of ion-selective electrodes (ISEs) with polymer membranes of different compositions. First electrode is based on Zr(IV)-tetraphenylporphyrin as ionophore selective towards carboxylic acid anions, the membrane of second one contains only liphophilic anion exchanger - tridodecylmethylammonium chloride. Final response of the system is a result of combination of EMF signals from both electrodes. Combination of two detectors enables significant decrease of differences between potentiometric signals induced by mixtures of studied anions of various concentrations as compared to results obtained only with metalloporphyrin-based ISE. The use of anion-exchanger based detector allows for elimination of the influence of aliphatic carboxylic acids lipophilicity.Proposed potentiometric flow-injection system was employed for determination of short-chain aliphatic carboxylic acids (so-called VFA - volatile fatty acids) in samples originating from an anaerobic digester. Results obtained for these relatively complicated samples are in good agreement with results obtained with the use of reference colorimetric method.Linear response towards carboxylic acids was observed in the concentration range of 10⁻⁴ to 10⁻² mol dm⁻³, with the slopes in the range of −110 to −150 mV dec⁻¹ (for acetate⁻ and butyrate⁻, respectively). System enables for determination of about 6 samples per hour. Life time of ISEs average about 2 months.     

Bis(2-mercaptobenzoxazolato)mercury(II) and bis(2-pyridinethiolato)mercury(II) complexes as carriers for thiocyanate selective electrodes

Highly selective poly(vinyl chloride) (PVC) membrane electrodes based on bis(2-mercaptobenzoxazolato)mercury(II) [Hg(MBO)₂] and bis(2-pyridinethiolato)mercury(II) [Hg(PT)₂] complexes as new carriers for thiocyanate-selective electrodes are reported. The electrodes were prepared by coating the membrane solution containing PVC, plasticizer, carriers and additives on the surface of graphite electrodes. Influence of the membrane composition, pH and possible interfering anions were investigated on the response properties of the electrodes. Both sensors exhibited Nernstian responses towards thiocyanate over a wide concentration range of 1×10⁻⁶ to 0.1 M, with slopes of 60.6±0.8 and 57.5±1.2 mV per decade of thiocyanate concentration for Hg(MBO)₂ and Hg(PT)₂ carriers, respectively, over a wide pH range of 3-11. The limit of detection for both electrodes was ∼6×10⁻⁷ M. The sensors have response times of ≤5 s and can be used for at least 2 months without any considerable divergence in their potential response. The proposed electrodes show fairly good discrimination of thiocyanate over several inorganic and organic anions. The electrodes were successfully applied to direct determination of thiocyanate in saliva and as indicator electrodes in precipitation titrations.     

Novel Poly(ethylene glycol)s Bearing Tributyltin Carboxylate End Groups as Ionophores in the Development of Chloride Ion‐Selective Electrodes

The potentiometric response characteristics of electrodes based on PVC membranes containing novel polyethylene glycols (PEGs) with tributyltin carboxylate end groups as ionophores for chloride ions were studied in 0.1 M HEPES solution, at the spontaneous pH. The effects of solvent mediator, amount of cationic additive, amount of ionophore and PEG chain length on the behavior of the sensors were investigated. The membranes with the best composition responded to chloride concentration in a linear range from 10^?4 to 10^?1 M Cl^? with a nearly Nernstian slope and a detection limit of 6.5×10^?5 M. The sensor showed a short response time (<25 s) in the whole concentration range and an operational lifetime of about one week for the most performing PVC membranes. In comparison with ISEs based on anion exchangers the interferences from the more lipophilic anions were greatly reduced, as inferable by the selectivity coefficients determined with the matched potential method at chloride concentration of 3.0×10^?3 M.     

Mimicking a Receptor for Cyanide Ion Based on Ion Imprinting and Its Applications in Potential Transduction

Using the strategy of template polymerization, a presynthesized specific metal‐complexing polymer (poly(methacryloylhistidine‐Ni(II)‐CN^?), Ni‐CN/IP) has been specifically used to recognize cyanide ion. As described previously, nickel(II)‐methacryloylhistidine dihydrate complex monomer was synthesized and reacted with KCN to produce the monomer‐template complex. This monomer‐template complex phase was polymerized in a dispersion medium. After polymerization, the template (CN^?) was removed from the Ni‐CN/IP, producing CN^? ion imprinted metal‐chelate polymer. The synthesized ion imprinted polymer is examined as a novel potential cyanide selective ionophore in polymeric membrane type ion selective electrodes. Membranes formulated with Ni‐CN/IP are shown to exhibit enhanced potentiometric selectivity for cyanide over more lipophilic anions including perchlorate, iodide, and thiocyanate. Addition of lipophilic cationic sites into the organic membranes enhanced the response and selectivity towards CN^? ion, while addition of lipophilic anionic sites deteriorated the response but enhanced the selectivity, indicating that the Ni‐CN/IP particles behaves via the so‐called “mixed‐mode” response mechanism. The fabricated sensors possessed good performance characteristics, in terms of life span, selectivity for CN^? ion over a wide range of other interfering anions, fast response, stability and high reproducibility. Applications for direct determination of cyanide ion in hazardous wastes using the proposed sensors showed good correlation with data obtained using commercial solid state cyanide electrode, with no significant difference in the t‐test values with 95 % confidence level. An F‐test revealed that the standard deviations of the replicate sample measurements obtained by the two methods were not significantly different.     

Selective detection of F− by chromogenic tetrazole receptor

A chromogenic anion host 4, containing two amide functionalities linked to azo dye and tetrazole rings, was synthesised and its complexes with various anions were investigated. The results show that receptor 4 can recognise selectively biologically important F^?  ion. The binding affinity for F^?  was investigated by naked-eye colour change, UV–vis and ¹H NMR spectroscopy. Addition of F^?  ion in CH₃CN and Dimethyl sulfoxide to receptor 4 causes a change in colour of the solution from colourless to yellow. The stoichiometry for host:anion is 1:1. Furthermore, receptor 4 was used as an ion carrier in ion-selective membrane electrodes. Selectivity of this membrane was studied towards various anions in water solution. Binding behaviour of receptor 4 towards several anions (Cl^? , F^? , Br^? , I^? ) has been investigated using density functional theory calculations.     

Aluminum(III) Porphyrins as Ionophores for Fluoride Selective Polymeric Membrane Electrodes

Aluminum(III) porphyrins are examined as potential fluoride selective ionophores in polymeric membrane type ion‐selective electrodes. Membranes formulated with Al(III) tetraphenyl (TPP) or octaethyl (OEP) porphyrins are shown to exhibit enhanced potentiometric selectivity for fluoride over more lipophilic anions, including perchlorate and thiocyanate. However, such membrane electrodes display undesirable super‐Nernstian behavior, with concomitant slow response and recovery times. By employing a sterically hindered Al(III) picket fence porphyrin (PFP) complex as the membrane active species, fully reversible and Nernstian response toward fluoride is achieved. This finding suggests that the super‐Nernstian behavior observed with the nonpicket fence metalloporphyrins is due to the formation of aggregate porphyrin species (likely dimers) within the membrane phase. The steric hindrance of the PFP ligand structure eliminates such chemistry, thus leading to theoretical response slopes toward fluoride. Addition of lipophilic anionic sites into the organic membranes enhances response and selectivity, indicating that the Al(III) porphyrin ionophores function as charged carrier type ionophores. Optimized membranes formulated with Al(III)‐PFP in an o‐nitrophenyloctyl ether plasticized PVC film exhibit fast response to fluoride down to 40 μM, with very high selectivity over SCN^?, ClO₄^?, Cl^?, Br^? and NO₃^? (k^pot<10^?3 for all anions tested). With further refinements in the membrane chemistry, it is anticipated that Al(III) porphyrin‐based membrane electrodes can exhibit potentiometric fluoride response and selectivity that approaches that of the classical solid‐state LaF₃ crystal‐based fluoride sensor.     

Ion-selective electrodes based on siderophores: Salicylate response of a ferrimycobactin membrane

Siderophores are compounds which transport iron across cell membranes; mycobactins are hydrophobic siderophores and were expected to be suitable for inclusion in the organic membrane phase of a liquid ion-exchange electrode responsive to iron(III) ions. In practice, no iron(III) response was obtained from mycobactin membranes (in a variety of solvents), but they did respond to salicylate ion with a sensitivity of 27–29 mV/decade over the range 2 × 10^?3–3 × 10^?2 mol l^?1 at pH 7. The effects of pH and interference by other anions are described and the possible mechanisms of the electrode are discussed. The selectivity of the electrode for salicylate is better than that of quaternary ammonium liquid ion-exchange electrodes.     

PVC‐Based on Thiopyrilium Derivatives Membrane Electrodes for Determination of Histamine

This study describes novel histamine‐selective electrodes, having their basis on thiopyrilium (TP) derivatives as suitable ionophores. The electrodes were prepared by incorporating the TP derivatives into plasticized poly(vinyl chloride) (PVC) membranes. These electrodes demonstrate high selectivity as far as the histamine response is considered, as compared with many common inorganic anions and other kinds of amino acids. The influence of membrane composition, pH and the effect of lipophilic cationic and anionic additives on the response characteristics of the electrode were investigated. The resulting sensor based on 2,6‐bis(4‐dimethyl amino phenyl)‐4‐phenyl thiopyrilium perchlorate (TP4) responds to histamine in a wide concentration range from 5.0 × 10^?6 to 1.0 × 10^?1 M with a slope of 54.8 ± 0.6 mV decade^?1 and detection limit of 3.0 μ mol L^?1 (～0.3 ppm). The electrode illustrates fast response time and good long‐term stability (more than 2 months). The ability to design histamine‐selective electrodes based on new thiopyrilium derivatives and both to alter selectivity and improve the response characteristics through structural changes to the charged ionophore, has been investigated. The prepared electrode was used for the determination of histamine in a synthetic human serum sample. Consequently, satisfactory recovery results were obtained over a wide concentration range of histamine.     

The potentiometric behavior of polymer-supported metallophthalocyanines used as anion-selective electrodes

Liquid polymer membrane electrodes based on nickel and manganese phthalocyanines were examined for use as anion-selective electrodes. The electrodes were prepared by incorporating the ionophores into plasticized poly(vinyl chloride) membranes, which were directly coated onto the surfaces of graphite electrodes. The resulting electrodes demonstrate near-Nernstian responses over a wide linear range of perchlorate anion (5 × 10⁻⁷ to 1 × 10⁻¹ M). The electrodes have a fast response time, submicromolar detection limits (5 × 10⁻⁷ M perchlorate), and could be used over a wide pH range of 3.5–10. The influences of lipophilic cationic and anionic additives on the response properties of the electrodes were investigated. The proposed sensors revealed high selectivity for perchlorate over a number of common inorganic and organic anions. The highest selectivity was observed for the electrode based on manganese phthalocyanine in the presence of the lipophilic anionic additive sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate. Application of the electrodes to determine perchlorate in tap water and human urine is also reported.      

Cyanide ion-selective electrodes based on thin electroplated membranes of silver chalcogenides: Part I. Membrane preparation and characterization

Cyanide-responsive ion-selective electrodes have been developed based on thin tellurium-doped silver selenide membranes electrodeposited on platinum substrates. The chemical composition of the electroplated film membranes could be expressed by the general formula Ag_2+δSe_1?xTe_x (where 0.2 < δ < 0.8 and 0.2 ? × ? 0.1). These electrodes exhibit a linear response in cyanide solutions with concentrations ranging from 10^?2 to 10^?6 M, with a slope of the electrode function of about 90 mV (pCN)^?1 (i.e., lower than the theoretically predicted double-Nernstian slope). These electrodes showed very stable behaviour during long-term investigation (several months). The conditions for the electrochemical preparation of cyanide-responsive silver chalcogenide membranes are discussed both from theoretical and practical points of view. X-ray diffraction, energy-dispersive x-ray fluorescence microanalysis (EDAX) and scanning electron microscopy (SEM) were used to examine the membrane composition, structure and surface morphology.     

Optical and electrochemical recognition studies of anions via novel benzothiazole azo-derivative

Herein, a novel supramolecular probe 4-(2-phenyldiazenyl)-2-(benzothiazol-2-yl) phenol (1) has been described, where assimilation of benzothiazole unit with azo functionality led to innovative electrochemical and optical response towards anions. The successful formation was confirmed using ¹HNMR, ¹³C NMR and HRMS. This rationally planned receptor 1 exhibits multi recognition modes in showing selectivity towards AcO^- and F^- anions by both visual and absorption processes; while I^- is sensed selectively via redox mechanism. The multi recognition mechanisms were thoroughly documented by DFT giving an insight picture of the mode of interaction of the anions in HOMO-LUMO energy levels ultimately affecting the activity of the designed benzothiazole moiety. Optimization of various parameters related to redox response was also analyzed by Taguchi method to minimize the effect of uncontrollable variables. Lower detection limit for the anions by different response mechanisms in a single moiety enhances the future possibility of an economic and time saving multichannel chemosensor.     

Selective electrodes for silver based on polymeric membranes containing calix[4]arene derivatives

Silver ion-selective electrodes were prepared with polymeric membranes based on two calix[4]arene derivatives functionalized by two hydroxy and two benzothiazolylthioethoxy groups. The electrodes all gave a good Nernstian response of 58?mV decade^–1 for silver in the activity range 5 × 10^–6–10^–1 M, the limits of detection reached 10^–5.8 M and exhibited high selectivity towards alkali, alkaline earth and some transition metal ions. The electrode was used as indicator electrode in titrations of Ag⁺ with Cl^– ion.     

Potentiometric sensors with membranes based on ionic liquid tetradecylammonium triethylammonio-<Emphasis Type="Italic">closo</Emphasis>-dodecaborate

Polymer compositions based on the ionic liquid tetradecylammonium triethylammonium-closododecaborate (TTCD) are proposed as the main components of membranes of potentiometric sensors (ion-selective electrodes) for determining ions [B₁₂H₁₁N(C₂H₅)₃]⁻. Two types of polymer compositions are considered: conventional, polyvinyl chloride (PVC)-liquid ion-exchanger (solution of TTCD in o-nitrophenyl octyl ether) and another, PVC-TTCD (ionophore-plasticizer). The optimal composition of membranes for both types of electrodes are proposed, and their main electroanalytical parameters, such as selectivity, effect of pH, range of linear response, reproducibility, and stability of potential, were measured. A comparative analysis of the electroanalytical parameters of potentiometric sensors with membranes of two types is given. The detection limits for the electrodes of types I and II are 9 × 10⁻⁷ and 4 × 10⁻⁷ M. It is shown that [B₁₂H₁₁N(C₂H₅)₃]⁻ anions can be determined by potentiometric titration with indicator electrodes of different types.     

Ion-selective membrane electrodes for the determination of the muscle relaxants pancuronium,tubocurarine, gallamine and succinylcholine

Ion-selective PVC membrane electrodes for the peripherial muscle relaxants pancuronium (PAN), tubocurarine (TUB), gallamine (GAL) and succinylcholine (SUC) are presented. The preparation of the electrode membranes contaimng ion pairs of the muscle relaxants with two different anionic counter ions, dipicrylaminate (DPA) and tetraphenylborate (TPB), are reported. The detection limits for all electrodes were ca. 10^?6 mol 1^?1 at physiological pH values and the measured slopes were dose to the values theoretically expected. Changes in the detection limits and the slopes of the electrodes in the pH range 2.5–11.0 were found to be due to reversible changes in the protonation state of the amine groups of the muscle relaxant (TUB) or the counter ion (DPA). The PAN-TPB and PAN-DPA ion-pair complexes were observed to have a bettet stability than those formed with TUB, GAL and SUC. The observed selectivity coefficients of the PAN-TPB electrodes were 10^?0.3 towards TUB and 10^?1.8 towards GAL.     

Evaluation of Ionic Liquids Based on Amino Acid Anions for Use in Liquid‐junction Free Reference Electrodes

In this paper we report on the novel polymeric membranes for the liquid junction‐free reference electrodes. The membranes contain the ionic liquids (ILs) based on the amino acid anions, namely valine‐, leucine‐, lysine‐ and histidine‐anions, and 1‐butyl‐3‐methylimidazolium cation. Addition of the ILs, and especially of the valine‐based one, to the polymeric plasticized membranes allows significant stabilization of the electrode potential and makes it insensitive to the solution composition. A simple criterion based on the calculated lipophilicities of the cation and anion of the IL is proposed for a priori estimation of its applicability for potential stabilization. The addition of the IL as a microcomponent is found to be advantageous over plasticizing the membrane with the IL due to better potential stability, higher dissociation degree and mobility of the species. The resistance of the novel reference membranes can be tuned by addition of the lipophilic membrane electrolytes, e. g. ETH500. The applicability of the developed reference electrodes is verified in the potentiometric calibration of the indicator K⁺‐ and Ca²⁺‐selective electrodes. Implementation of the amino acid‐based ionic liquids with low environmental toxicity can make a significant contribution to the development of nature‐friendly potentiometry.     

Recognition of anions and monocarboxylic acids by a fluorescent guanidine-based receptor

A guanidine-based fluorescent receptor has been synthesised to study its binding behaviour towards anions (F^? , Cl^? , Br^? , I^?  and AcO^? ). The two donor N–H bonds of the receptor do not point in the same direction; rather, one N–H bond is intramolecularly hydrogen-bonded with the carbonyl oxygen atom. The nature of the donor–acceptor (DA) arrangement induces moderate binding properties. The binding behaviour towards monocarboxylic acids (benzoic acid and phenylacetic acid) is also compared. The binding behaviour of receptor 1 towards the F^?  anion is higher among the anions studied, whereas in the case of monocarboxylic acid, the binding constant with phenylacetic acid is higher than benzoic acid.     

Iodide‐Selective Electrodes Based on Bis[N(2‐methyl‐phenyl) 4‐Nitro‐thiobenzamidato]mercury(II) and Bis[N‐phenyl 3,5‐Dinitro‐thiobenzamidato]mercury(II) Carriers

Highly selective poly(vinyl chloride) (PVC) membrane electrodes based on recently synthesized mercury complexes including Hg(Nmpntb)₂ and Hg(Npdntb)₂ as new carriers for iodide‐selective electrodes by incorporating the membrane ingredients on the surface of graphite electrodes are reported. The effect of various parameters including the membrane composition, pH and possible interfering anions were investigated on the response properties of the electrodes. Both sensors exhibited Nernstian responses toward iodide over a wide concentration range of 7×10^?7 to 0.1 M and 1×10^?6 to 0.1 M, with slopes of 59.6±0.8 and 58.9±0.9 mV per decade of iodide concentration and detection limit of 3×10^?7 M and 7×10^?7 for Hg(Npdntb)₂ and Hg(Nmpntb)₂, respectively, over a wide pH range of 3–11. The sensors have response times of ≤5 s and can be used for at least 2 months without any considerable divergence in their potential response. The proposed electrodes show good ability to discriminate iodide over several inorganic and organic anions. The electrodes were successfully applied to direct determination of iodide in synthetic mixture, waste water and drinking water and as indicator electrodes in precipitation titrations.