Selective Membrane Electrode Research Articles

테트라싸이크린 항생제를 담체로 이용한 막전극의 전위차 특성

본 연구에서는 테트라싸이크린 항생제를 양이온선택성 전극의 담체로 사용한 막전극을 제작하고 알칼리 및 알칼리 토금속에 적용하여 전위차 감응도를 조사하였다. 제작된 전극은 지용성 첨가제의 유무와 관계없이 <TEX>$Ca^{2+}$</TEX> 이온에 대해서 거의 이상적인 전위차 감응도를 나타내었다. 또한 <TEX>$Mg^{2+}$</TEX>를 제외한 다른 양이온에도 이상적인 네른스트값에 80% 이상의 감응도와 <TEX>$10^{-5}$</TEX> 이하의 검출한계를 나타내었다. 수명, 감응시간, 재현성 등도 이온선택성 전극에 응용하기에 문제가 없었다. The main component governing selectivity in ion-selective electrodes and optodes is the ionophore. For this reason, a member of natural products that possess selective ion-binding properties have long been sought after. By applying this principle, the performance of tetracycline used as neutral carriers for cation selective polymeric membrane electrode was investigated. The cation ion-selective electrode based on tetracycline gave a good Nernstian response of 26.6 mV per decade for calcium ion in the activity range <TEX>$1x10^{-6}M$</TEX> to <TEX>$1x10^{-2}M$</TEX> with and without lipophilic additives. The optimized cation ion-selective membrane electrodes displayed very comparable potentiometric responses to various mono and di-valent cations of alkali and alkaline earth metal ions except <TEX>$Mg^{2+}$</TEX>.

Fast response and selective perchlorate polymeric membrane electrode based on bis(dibenzoylmethanato) nickel(II) complex as a neutral carrier

The feasibility of a synthesized bis(dibenzoylmethanato) Ni(II) complex (Ni(DBM) 2), as a novel ionophore for the preparation of a solid ion selective polymeric membrane (PVC) was tested. The ionophore has shown with the enhanced potentiometric selectivity toward perchlorate compared to other anions. The selectivity sequence of this electrode is as follows: ClO 4 − > SCN − > I − > CN − > ClO 3 − > NO 3 − > Br − > SO 3 − > BrO 3 − > F − > Cl −, which is a Hofmeister selectivity sequence. The proposed electrode possesses a very wide Nernestian potential linear range to perchlorate from 1.0 × 10 −6 to 1.0 × 10 −1 M (0.138 μg mL −1 to 138 mg mL −1), a low detection limit (6.6 × 10 −7 M) and good perchlorate selectivity over the wide variety of other anions. The developed electrode has an especially fast response (<5 S) and a wide pH independent range (1.2–12.5) in comparison with recent reported electrodes. The proposed electrode was used for the determination of perchlorate in water samples and human urine with satisfactory results.

A novel thiocyanate-selective electrode based on a zinc–phthalocyanine complex

A novel thiocyanate (SCN-)-selective PVC membrane electrode based on a zinc-phthalocyanine (ZnPc) complex as neutral carrier is described. The membrane electrode containing ZnPc with 5.1% (w/w) ionophore, 29.2% (w/w) PVC, and 65.7% (w/w) 2-nitrophenyl octyl ether (o-NPOE) as plasticizer displayed an anti-Hofmeister selectivity sequence, SCN- > Sal- > I- > ClO4- > Br- > Cl- > NO3- > NO2- > H2PO4- > SO4(2-)), and exhibited near-Nernstian potential response to thiocyanate ranging from about 1.0 x 10(-1) to 1.0 x 10(-6) mol L(-1) with a detection limit of 7.5 x 10(-7) mol L(-1) and a slope of 58.1+/-0.5 mV per decade in pH 3.0 phosphate buffer solution at 25 degrees C. This preferential response is believed to be associated with the unique coordination between the central metal of the carrier and thiocyanate.

Perchlorate selective membrane electrodes based on synthesized platinum(II) complexes for low-level concentration measurements

Three synthesized platinum(II) complexes, [PtR 2(NN)] (R = Me, p-MeC 6H 4 and p-MeOC 6H 4; NN = 2,2′-bipyridyl), were studied to characterize their ability as an anion carrier in a PVC membrane electrode. The polymeric membrane electrodes (PME) and also coated glassy carbon electrodes (CGCE) prepared with [Pt( p-MeOC 6H 4) 2(NN)] showed excellent response characteristics to perchlorate ions. The electrodes exhibited Nernstian responses to ClO 4 − ions over a wide concentration range from 5 × 10 −7 to 4.0 × 10 −1 M for PME and 1.5 × 10 −7 to 2.7 × 10 −1 M for CGCE with low detection limits (4.0 × 10 −7 M for PME and 1.0 × 10 −7 M for CGCE). The electrodes possess fast response time, satisfactory reproducibility, appropriate lifetime and, most importantly, good selectivity toward ClO 4 − relative to a variety of other common anions. The potentiometric response of the electrodes is independent of the pH of the test solution in the pH range 2.5–9.5. The proposed sensors were used in potentiometric determination of perchlorate ions in mineral water, urine samples and also samples containing interfering anions. The interaction of the ionophore with perchlorate ions was shown by UV–vis spectroscopy.

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 ionselective 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 mM, with very high selectivity over SCN � , ClO4 � ,C l � ,B r � 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.

Application of new membrane selective electrodes for the determination of drotaverine hydrochloride in tablets and plasma

The construction and electrochemical response characteristics of poly vinyl chloride (PVC) membrane sensors for the determination of drotaverine hydrochloride were described. The sensors are based on the use of the ion association complexes of drotaverine cation with sodium phosphotungestate (Dro-PTA) or ammonium reineckate (Dro-R) counter anions as ion exchange sites in the PVC matrix. The performance characteristics of these sensors, which were evaluated according to IUPAC recommendations, reveal a fast, stable and linear response for drotaverine over the concentration range 10 −5 to 10 −2 M with cationic slopes of 49.55 and 51.36 mV per concentration decade. The direct potentiometric determination of drotaverine hydrochloride using the proposed sensors gave average recoveries of 99.95 ± 0.71 and 100.04 ± 0.60 for Dro-PTA and Dro-R, respectively. The sensors are used for determination of drotaverine hydrochloride in tablets, in its mixture with caffeine and paracetamol and in plasma. Validation of the method shows suitability of the proposed sensors for use in the quality control assessment of drotaverine hydrochloride. The developed method was found to be simple, accurate and precise when compared with a reported HPLC method.

A bromide selective polymeric membrane electrode based on Zn(II) macrocyclic complex

A novel bromide ion-selective PVC membrane sensor based on 2,3,10,11-tetraphenyl-1,4,9,12-tetraazacyclohexadeca-1,3,9,11-tetraene zinc(II)complex ( I) as carrier has been developed. The electrode exhibited wide working concentration range 2.2 × 10 −6 to 1.0 × 10 −1 M and a limit of detection as 1.4 × 10 −6 M with a Nernstian slope of 59.2 ± 0.5 mV per decade. The response time of electrode was 20 s over entire concentration range. The electrode possesses the advantages of low resistance, fast response and good selectivities for bromide over a variety of other anions and could be used in a pH range of 3.5–9.5. It was successfully used as an indicator electrode in the potentiometric titration of bromide ions with silver ion and also in the determination of bromide in real samples.

Response Behavior of Poly(vinyl chloride)‐ and Polyurethane‐Based Ca2+‐Selective Membrane Electrodes with Polypyrrole‐ and Poly(3‐octylthiophene)‐Mediated Internal Solid Contact

AbstractThe potentiometric response behavior of Ca2+‐selective poly(vinyl chloride) (PVC) and polyurethane (PU) membranes with different inner contacts has been compared. Evidence for the formation of a water film between membrane and internal contact and, hence, a less than optimal lower detection limit have been found for membranes directly in contact with bare Au or with polypyrrole generated by electropolymerization in the presence of KCl. A significantly better behavior is shown by membranes with polypyrrole prepared in the presence of potassium hexacyanoferrate. Best performances have been obtained with solvent‐cast poly(3‐octylthiophene) as the internal contacting layer. As compared with the PVC membranes, those with PU had a significantly worse performance throughout.

Copper (II) Ion Selective Liquid Membrane Electrode Based on New Schiff Base Carrier

Cu2+ selective PVC membrane electrode based on new Schiff base 2, 2'-[1,9 nonanediyl bis (nitriloethylidyne)]-bis-(1-naphthol) as a selective carrier was constructed. The electrode exhibited a linear potential response within the activity range of 1.0 x 10(-6) - 5.0 x 10(-3) moll(-1) with a Nernstian slope of 29 +/- 1 mV decade(-1) of Cu2+ activity and a limit of detection 8.0 x 10(-7) mol l(-1). The response time of the electrode was fast, 10 s, and stable potentials were obtained within the pH range of 3.5- 6.5. The potentiometric selectivity coefficients were evaluated using two solution method and revealed no important interferences except for Ag+ ion. The proposed electrode was applied as an indicator electrode to potentiometric titration of Cu2+ ions and determination of Cu2+ content in real samples such as black tea leaves and multivitamin capsule.

Highly selective and sensitive thiocyanate membrane electrode based on nickel(II)-1,4,8,11,15,18,22,25-octabutoxyphthalocyanine

A highly selective membrane electrode based on nickel(II)-1,4,8,11,15,18,22,25-octabutoxyphthalocyanine (NOBP) is presented. The proposed electrode shows very good selectivity for thiocyanate ions over a wide variety of common inorganic and organic anions. The sensor displays a near Nernstian slope of −58.7 ± 0.6 mV per decade. The working concentration range of the electrode is 1.0 × 10 −6 to −1.0 × 10 −1 M with a detection limit of 5.7 × 10 −7 M (33.06 ng/mL). The response time of the sensor in whole concentration ranges is very short (<10 s). The response of the sensor is independent on the pH range of 4.3–9.8. The best performance was obtained with a membrane composition of 30% PVC, 65% dibutyl phthalate, 3% NOBP and 2% hexadecyltrimethylammonium bromide. It was successfully applied to direct determination of thiocyanate in biological samples, and as an indicator electrode for titration of thiocyanate ions with AgNO 3 solution.

A thermodynamic study on the interaction between magnesium ion and human growth hormone

A thermodynamic study on the interaction between magnesium ion and human growth hormone (hGH) was studied at 27 degrees C in NaCl solution (50 mM) using different techniques. Two techniques of ionmetry using a Mg2+selective membrane electrode and isothermal titration calorimetry were applied to obtain the binding isotherm for hGHMg2+; results obtained by both techniques were found to be in good agreement. There is a set of three identical and noninteracting binding sites for magnesium ions. The intrinsic dissociation equilibrium constant and the molar enthalpy of binding are 46 microM and -17.7 kJ/mol, respectively. Temperature scanning UV-visible spectroscopy was applied to elucidate the effect of Mg2+ binding on the protein stability, and circular dichroism (CD) spectroscopy was used to show the structural change of hGH due to the metal ion interaction. Magnesium ion binding increased the protein thermal stability by increasing the alpha-helix content as well as decreasing both beta and random coil structures. However, the secondary structural change of the protein returns to its native form, including a small change in the tertiary structure, in high concentrations of magnesium ion.

Effects of calcium binding on the structure and stability of human growth hormone

Thermodynamic analysis of calcium ions binding to human growth hormone (hGH) was done at 27 °C in NaCl solution, 50 mM, using different techniques. The binding isotherm for hGH-Ca 2+ was obtained by two techniques of ionmetry, using a Ca 2+-selective membrane electrode, and isothermal titration calorimetry. Results obtained by two ionmetric and calorimetric methods are in good agreement. There is a set of three identical and non-interacting binding sites for calcium ions. The intrinsic dissociation equilibrium constant and the molar enthalpy of binding are 52 μM and −17.4 kJ/mol, respectively. Temperature scanning UV–vis spectroscopy was applied to elucidate the effect of Ca 2+ binding on the protein stability, and circular dichroism (CD) spectroscopy was used to show the structural change of hGH due to the metal ion interaction. Calcium ions binding increase the protein thermal stability by increasing of the alpha helix content as well as decreasing of both beta and random coil structures.

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.

Gallium(III)‐Schiff Base Complexes as Novel Ionophores for Fluoride Selective Polymeric Membrane Electrodes

AbstractGallium(III)‐Schiff base complexes are examined as potential ionophores for the development of fluoride ion‐selective polymeric membrane electrodes. To probe the effect of ionophore structure, several different salen and salophen compounds have been synthesized and tested in plasticized poly(vinyl chloride) membranes (H21–5). A salophen ligand structure highly substituted with t‐butyl groups (H21) was found to be optimal with respect to membrane compatibility, and its corresponding Ga(III) complex yields membrane electrodes with greatly enhanced potentiometric selectivity for fluoride ion over a host of other anions. Addition of lipophilic anionic sites into the membrane phase provides optimized response and selectivity, indicating that the Ga1 ionophore functions as a charge carrier. The use of dioctylsebacate as the membrane plasticizer helps reduce any dimer‐monomer equilibria in the membrane phase, yielding sensors with rapid and fully reversible EMF response. Optimal potentiometric detection of fluoride is achieved in solutions buffered to relatively low pH values (pH 3.0), to reduce anionic response to hydroxide. The use of gallium(III)‐Schiff base complexes is shown to offer a promising research direction to ultimately achieve polymeric membrane fluoride sensors that exhibit potentiometric response equivalent to the classical lanthanum fluoride‐based solid state type membrane electrode.

A Selective Membrane Electrode for Thiocyanate Ion Based on a Bis‐taurine‐salicylic Binuclear Copper(II) Complex as Ionophore

AbstractThe response characteristics of a new potentiometric membrane electrode with unique selectivity towards thiocyanate ion were reported. The electrode was prepared by incorporating bis‐taurine‐salicylic binuclear copper(II) complex into a plasticized PVC‐membrane. The resulting electrode exhibits anti‐Hofmeister selectivity sequence: SCN−&gt;I−&gt;ClO4−&gt;Sal−&gt;NO3−&gt;NO2−&gt;Br−&gt;Cl−&gt;SO3−&gt;SO42− and a near‐Nernstian potential linear range for thiocyanate from 1.0Å×10−1 to 1.0Å×10−6 mol·L‐1 with a detection limit of 8.0Å×10−7 mol·L−1 and a slope of −56.5 mV/pc in phosphate buffer solution of pH 5.0 at 20°C. The UV/Vis spectra, IR spectroscopy and AC impedance studies showed that the excellent selectivity to thiocyanate was related to the unique interaction between the central metal and the analyte and a steric effect associated with the structure of the carrier. The electrode was successfully applied to the determination of thiocyanate in waste water and human urine samples.

Iodide-selective membrane electrode based on salophen complex of cobalt (III)

A highly selective PVC membrane electrode based on a cobalt-salophen complex was prepared. The sensor displays an anti-Hofmeister selectivity sequence with a preference for iodide ion over many common anions. The electrode has a linear dynamic range between 5.0×10-7 to 1.0×10-1 mol L-1, with a Nernstian slope of -58.9 mV decade-1 and a detection limit of 3.0×10-7 mol L-1. The working pH range of the sensor is 3.1-9.8. It exhibits of a fast as 15 s and has a lifetime of about 2 months. The selectivity coefficients for the proposed electrode were improved for some interferences, when compared with those of available iodide membrane electrode. The proposed electrode was successfully applied for the direct determination of iodide in edible salt and as an indicator electrode in potentiometric titration of I- against Ag+.

A novel naphazoline-selective membrane sensor and its pharmaceutical applications

New naphazoline (NPZ) ion selective membrane electrodes of both conventional and coated graphite types were prepared based on the ion-pair of naphazoline tetraphenylborate (NPZ–TPB). The conventional type electrode was fully characterized in terms of membrane composition, life span, pH, ionic strength and temperature. The electrode exhibited a Nernstian response for naphazoline in the concentration range 1.0 × 10 −5 to 5.0 × 10 −2 and 5.0 × 10 −6 to 5.0 × 10 −2 M with a slope of 58.4 ± 1.1 and 57.0 ± 0.1 mV/concentration decade and a limit of detection of 4.0 × 10 −6 and 2.5 × 10 −6 M for conventional and coated graphite types, respectively. It could be used in the pH range 3.0–8.0. It was applied to potentiometric determination of naphazoline in pure state and pharmaceutical preparation under batch conditions. The selectivity of the electrode toward a large number of inorganic cations, sugars and amino acids was tested. The solubility product of the ion-pair and the formation constant of the precipitation reaction leading to the ion-pair formation were determined conductometrically.

Be(II) Graphite Coated Membrane Sensor Based on a Recently Synthesized Benzo‐9‐Crown‐3 Derivative

AbstractA highly sensitive and selective membrane electrode with 9‐crown‐3 derivative (CD) as ionophore, potassium tetrakis‐(p‐chlorophenyl) borate as anionic additive (KTB), acetophenone (AP) as solvent mediator was prepared and investigated as a Be(II) sensor. The best performance was observed with the membrane having the percent ratio 30% PVC: 8% CD: 6% KTB: 56% Acetophenone. The poly(vinyl chloride) PVC membrane containing 9‐crown‐3 derivative (CD) directly coated on a graphite electrode, shows a Nernstian response for Be(II) ions over a very wide concentration range (1.0×10−1−1.0×10−7 M) with a detection limit of 8.0×10−8 M (ca. 0.72 ng/mL). It has a fast response time of ca. 20 s and can be used for at least 10 weeks without any major deviation in potential. The proposed sensor exhibits very good selectivity with respect to common alkali, alkaline earth, transition and heavy metal ions. The proposed sensor was used as end point indicator electrode in the titration of Be(II) ions with EDTA. It was also applied to determination of Be(II) in real sample.

The Interaction between Hexadecyltrimethylammonium Bromide to Poly (Ethylene Glycol) with Different Molecular Weights and Some Schiff-Bases Investigated by Surfactant Ion Selective Electrode

The interaction between ionic surfactants and different nonionic molecules and polymers are studied using ion surfactant selective electrode. From the experimental data, critical concentrations of the interaction and binding process are evaluated. The interaction between hexadecyltrimethylammonium bromide (HTAB) with polyethylene glycol (PEG) in three molecular weights (1000, 10000 and 100000) and also schiff-bases, 2-[2-carboxyphenyl nitrilomethylidyne]-phenol (ortho CNP), 2-[3-carboxyphenyl nitrilomethylidyne]-phenol (meta CNP)and 2-[4-carboxyphenyl nitrilomethylidyne]-phenol (para CNP) with the potentiometric method were investigated using HTAB membrane selective electrode. In the case of PEG with increasing molecular weights more interaction to HTAB occurs. The electromotive force (EMF) data also showed that interaction between para CNP with HTAB is more than the other schiff-bases. It seems this case related to less space interference of COOH group for that compound. The onset of bi nding (T 1 ) of course is the same for three schiff-base molecules.

Cs +-selective membrane electrodes based on ethylene glycol-functionalized polymeric microspheres

A new strategy for improving the robustness of membrane-based ion-selective electrodes (ISEs) is introduced based on the incorporation of microsphere-immobilized ionophores into plasticized polymer membranes. As a model system, a Cs +-selective electrode was developed by doping ethylene glycol-functionalized cross-linked polystyrene microspheres (P-EG) into a plasticized poly(vinyl chloride) (PVC) matrix containing sodium tetrakis-[3,5-bis(trifluoromethyl)phenyl] borate (TFPB) as the ion exchanger. Electrodes were evaluated with respect to Cs + in terms of sensitivity, selectivity, and dynamic response. ISEs containing P-EG and TFPB that were plasticized with 2-nitrophenyl octyl ether (NPOE) yielded a linear range from 10 −1 to 10 −5 M Cs +, a slope of 55.4 mV/decade, and a lower detection limit (log a Cs) of −5.3. In addition, these membranes also demonstrated superior selectivity over Li +, Na +, and alkaline earth metal ion interferents when compared to analogous membranes plasticized with bis(2-ethylhexyl) sebacate (DOS) or membranes containing a lipophilic, mobile ethylene glycol derivative (ethylene glycol monooctadecyl ether (U-EG)) as ionophore.