The synthesis of bis(benzo-crown ether)s and their incorporation into potassium-selective PVC membrane electrodes

Five bis(benzo-15-crown-5) derivatives connected with different bridge chains were synthesized as neutral carriers in K⁺-selective electrodes. Potassium ion-selective PVC membrane electrodes based on these bis(crown ether)s were prepared using dibutyl phthalate (DBP) and dioctyl phthalate (DOP) as plasticizers of the PVC membrane. The selectivity coefficients (K _M ⁿ⁺:K _K+) for various alkali and alkaline-earth metal ions were measured. The electrodes based on the bis(crown ether)s are more selective for K⁺ than those based on monomeric crown ethers. The selectivity of one of the prepared potassium selective electrodes was higher than that of the electrode based on valinomycin and three of them were stable over a wide pH range.     

Hyamine 1622 - Selective PVC Membrane Electrodes Based on bis (Crown Ether)s

Abstract

Hyamine 1622 - selective PVC membrane electrodes based on bis (crown ether)s containing the benzo - 18 - crown - 6 moiety were prepared, using o - nitrophenyloctylether (NPOE) or dipentylphthalate (DPP) as the plasticizer of the PVC membrane. Selectivity coefficients for various interfering ions (inorganic and organic cations), were determined by the mixed solution method. The selectivity of the respective electrodes was found to be affected by the kind of plasticizer employed, and NPOE seemed to be a more suitable plasticizer than DPP. The NPOE electrode system based on the bis (crown ether) that has 11 atoms between the two benzo-18-crown-6 moieties offers the advantage of greater selectivity. The electrodes show excellent electrode properties, and the electrode response was stable in a wide pH range.     

Mebendazole selective membrane sensor and its application to pharmaceutical analysis.

A PVC membrane sensor for the selective determination of mebendazole (MBZ) was fabricated. The sensor is based on an ion association of MBZ with silicotungstic acid (STA) as ion pair and bis(2-ethylhexyl)phthalate (BEP) as the plasticizing agent in a PVC matrix. The sensor showed a linear response for MBZ for a concentration range 1.0x10(-6)-5.0x10(-2) M with a Nernstian slope of 55.8 mV/decade (limit of detection 6.3x10(-7) M) in the pH range 4-7. It has a fast response time of <30 s. The sensor showed a very good selectivity for MBZ with respect to a large number of ions. The direct determination of MBZ in pharmaceutical formulations gave results that compare well with the data obtained from the standard method.     

Some High Molecular Weight Phthalate Plasticizers for Poly (Vinyl Chloride) Resins

Naphthenic acids and alcohols were prepared by oxidation of naphthenes. Four different high molecular weight phthalates of the types bis-2-naphthene carboxyethyl phthalate and ethylene glycol bis(naphthenyl phthalate). These high molecular weight phthalates and di-n-octyl phthalate (DNOP), as a reference commercial plasticizer, were compounded with poly (vinyl chloride) (PVC) and evaluated as plasticizers. The high molecular weight phthalates were more sensitive to soapy water than DNOP. Volatility and resistance to kerosene extraction studies were markedly better than for DNOP. The new plasticizers have good compatibility with PVC resin.     

Potentiometric Anion Selectivity and Analytical Applications of Polymer Membrane Electrodes Based on Novel Mn(III)‐ and Mn(IV)‐Salophen Complexes

New Mn(III)‐L and Mn(IV)‐L complexes were prepared from the highly lipophilic salophen ligand (L): phenol 2,2′‐[(4,5‐dimethyl‐1,2‐phenylene)bis[(E)‐nitrilomethylidyne]]bis[4,6‐bis(1,1‐dimethylethyl). The prepared complexes were fully characterized and used for the construction of thiocyanate membrane electrodes. Optimized membrane electrodes contained 33.0 mg PVC, 66.0 mg o‐nitrophenyloctylether, 50 or 5 (mole %) tetrakis(trifluoromethyl)phenyl borate and 1 mg Mn(III)‐L (sensor 2) or Mn‐(IV)‐L (sensor 12), respectively. Such electrodes exhibited linear responses toward thiocynate in a concentration range of 10^?1–10^?5 M and detection limits of 8.3×10^?6, 8.9×10^?6 M for sensor 2 and 12, respectively. Optimized membrane electrodes exhbited high selectivty toward thiocayante compared to more lipophilic anions. The observed thiocyanate selectivity of the optimized membranes was confirmed by formation constant calculations for Mn(III)‐L and Mn(IV)‐L with SCN^?, β=10^14.1 and 10^12.5, which was measured potentiometrically using the sandwich membrane method. Furthermore, computational study using DFT calculations was performed to at DFT/B3LYP level of theory to confirm the observed selectivity data. The response times were 3 and 0.5 min for low and high concentrations. The lifetimes of the optimized electrodes were ～4–6 weeks. The analytical utility of the optimized membrane electrodes was demonstrated by the analysis of thiocyanate level in different saliva samples.     

Nitron tetrachloroaurate(III) electrodes with poly(vinyl chloride) and liquid membranes for the selective determination of gold

PVC matrix and liquid membrane electrodes have been developed for direct potentiometric determination of gold(III). The membranes incorporate nitron tetrachloroaurate(III) as electroactive material. Fast response for gold(III) over the concentration range 10(-5)-0.1M, with response slopes of 52.8-55.2 mV/decade is obtained. The electrodes show good selectivity for gold(III) at pH 2-5 in the presence of many anions and cations. The PVC membrane electrode offers the advantages of greater selectivity (except for Cr(3+), Mn(2+) and ClO(-)(4)) and higher thermal stability. The liquid membrane electrode gives a higher response slope and faster time of response than the PVC membrane electrode. Determination of AuCl(-)(4) over the range 2 mug/ml-2 mg/ml shows an average recovery of 98.5% and a mean standard deviation of 1.0%. Determination of gold in some gold alloys (58.3-99.9% Au) and pharmaceutical preparations gave an average recovery of 99.4% and a mean standard deviation of 0.7%, which are comparable with the performance obtained with the spectrophotometric Malachite Green and gravimetric U.S. Pharmacopeia methods.     

The synthesis of bis(benzo-15-crown-5) derivatives and their use in potassium-PVC membrane electrodes

Five new bis(benzo-15-crown-5) derivatives with different connecting groups were synthesized. Potassium ion-selective PVC membrane electrodes based on these bis(crown ether)s were prepared and their selective properties were measured. The results showed that most of these electrodes are stable over a wide pH range and their selectivity coefficients were better than those of an electrode based on natural valinomycin.     

A perfume odour-sensing system using an array of piezoelectric crystal sensors with plasticized PVC coatings

Using PVC polymer as membrane matrix and di-n-octylphenyl phosphate (DOPP) as plasticizer, a piezoelectric crystal sensor (PCS) array with 12 adsorptive materials selected from 68 compounds by cluster analysis has been constructed as a perfume odour-sensing system. The frequency shift data obtained from the sensor array responding to four commercial perfume odours are first autoscaled and then treated by principal component analysis. The experimental results show that the plasticized PVC membrane PCS array provides improved performance of pattern recognition compared with the single adsorptive coating PCS array. The frequency shift response characteristics of these sensors have been investigated experimentally. The proposed sensor array has also been applied to the classification of commercial spirituous liquor, wine and soft drink samples, as well as aliphatic alcohol homologues and isomers.     

A perfume odour-sensing system using an array of piezoelectric crystal sensors with plasticized PVC coatings

Using PVC polymer as membrane matrix and di-n-octylphenyl phosphate (DOPP) as plasticizer, a piezoelectric crystal sensor (PCS) array with 12 adsorptive materials selected from 68 compounds by cluster analysis has been constructed as a perfume odour-sensing system. The frequency shift data obtained from the sensor array responding to four commercial perfume odours are first autoscaled and then treated by principal component analysis. The experimental results show that the plasticized PVC membrane PCS array provides improved performance of pattern recognition compared with the single adsorptive coating PCS array. The frequency shift response characteristics of these sensors have been investigated experimentally. The proposed sensor array has also been applied to the classification of commercial spirituous liquor, wine and soft drink samples, as well as aliphatic alcohol homologues and isomers.     

Nitrate-selective membrane electrode based on bis(2-hydroxyanil)acetylacetone lead(II) neutral carrier.

A nitrate-selective electrode based on a recently synthesized bis(2-hydroxyanil)acetylacetone lead(II) complex [(haacac)Pb] has been developed. Among different compositions studied, a membrane containing 30.7% poly(vinyl chloride) (PVC), 61.3% dibutyl phthalate (DBP) as a plasticizer, 3% methyltrioctylammonium chloride (MTOAC) as a cationic additive and 5% ionophore (all w/w) exhibited the best potentiometric response toward nitrate ion in aqueous solutions. The potentiometric response of the electrode was linear with a Nernstian slope of -58.8 mV decade(-1) within the NO3- concentration range of 2 x 10(-5)-1 x 10(-1) mol dm(-3). The response time of the electrode was < or =10 s over the entire linear concentration range of the calibration plot. The electrode is suitable for use within the pH range of 5.3-11. The selectivity coefficients for the proposed electrode were improved for some interferences, when compared with those of commercially available nitrate-selective electrodes.     

Radiotracer studies on calcium ion-selective electrode membranes based on poly(vinyl chloride) matrices

Radiotracer studies with ⁴⁵Ca and ³⁶Cl demonstrate that PVC matrix membranes containing Orion 92-20-02 liquid calcium ion-exchanger are permselective to counter-cations. Diffusion coefficients are quoted for the migration of ⁴⁵Ca between pairs of calcium solutions and are discussed in terms of solution concentration, membrane thickness and concentration level of sensor in the membrane. Migration of calcium ions from calcium chloride solution to a Group (II) metal chloride solution through a PVC membrane containing calcium liquid ion-exchanger is discussed in terms of solvent extraction and electrode selectivity coefficient parameters. Thus, magnesium, strontium and barium ions appear to inhibit migration through the membrane by their low affinity for the membrane liquid ion-exchanger sites, while the inhibition by beryllium ions is attributed to site blockage by the strong affinity of dialkylphosphate sites for beryllium.     

FIA Potentiometric and Solvent Extraction Studies of Alkali Metal and Alkaline Earth Cation Complexation by bis(Tert-butylbenzo)-21-crown-7

Abstract

A flow injection analysis study of the potentiometric selectivity of bis[4(5)-tert-butylbenzo]-21-crown-7 (D(tBB)21C7) for cesium over the other alkali metal cations and three alkaline earth cations has been conducted. A PVC matrix membrane containing D(tBB)21C7 as an ionophore was coated on the tip of a silver wire incorporated in a flow cell. No selectivity for cesium over rubidium and only low selectivity over potassium were noted. However, very high selectivities for cesium over sodium, lithium, strontium, calcium, and magnesium were observed. Selectivity of D(tBB)21C7 in the solvent extraction of alkali metal cations was determined by the picrate extraction method. The percent extraction into deuteriochloroform decreased in the order cesium, rubidium > potassium » sodium » lithium. Thus good agreement was observed between the responses of D(tBB)21C7 towards alkali metal cations in polymeric membrane electrodes and in solvent extraction.     

New polymeric membrane cadmium(II)-selective electrodes using tripodal amine based ionophores

Fabrication of PVC membrane electrodes incorporating selective neutral carriers for Cd(2+) was reported. The ionophores were designed to have different topologies, donor atoms and lipophilicity by attaching tripodal amine (TPA) units to the lipophilic anthracene (ionophore I) and p-tert-butylcalix[4]arene (ionophores II, III and IV). The synthesized ionophores were incorporated to the plasticized PVC membranes to prepare Cd(II) ion selective electrodes (ISEs). The membrane electrodes were optimized by changing types and amounts of ionic sites and plasticizers. The selectivity of the membranes fabricated from the synthesized ionophores was evaluated, the relationship between structures of ionophores and membrane characteristics were explored. The ionophore IV which composed of two opposites TPA units on the calix[4]arene compartment showed the best selectivity toward Cd(2+). The best membrane electrode was fabricated from ionophore IV (10.2 mmol kg(-1)) with KTpClPB (50.1 mol% related to the ionophore) as an ion exchanger incorporated in the DOS plasticized PVC membrane (1:2; PVC:DOS). The Cd-ISE fabricated from ionophore IV exhibited good properties with a Nernstian response of 29.4±0.6 mV decade(-1) of activity for Cd(2+) ions and a working concentration range of 1.6×10(-6)-1.0×10(-2)M. The sensor has a fast response time of 10s and can be used for at least 1 week without any divergence in potential. The electrode can be used in the pH range of 6.0-9.0. The proposed electrodes using ionophores III and IV were employed as a probe for determining Cd(2+) from the oxidation of CdS QDs solution and the real treatment waste water sample with excellent results.     

Ion-selectivity of plasticizers in poly(vinyl chloride) membrane electrodes

Electrode membranes were presented which contained only PVC and a plasticizer. The plasticizers studied were tris(2-ethylhexyl)phosphate, 2-nitrophenyl octyl ether and bis(1-butylpentyl)adipate. The response and selectivity of these ligand-free PVC electrodes towards alkali and alkaline earth cations are reported.     

Room Temperature Ionic Liquids (RTILs) and Multiwalled Carbon Nanotubes (MWCNTs) as Modifiers for Improvement of Carbon Paste Ion Selective Electrode Response; A Comparison Study with PVC Membrane

Room temperature ionic liquids (RTILs), 1‐n‐butyl‐3‐methylimidazolium tetrafluoroborate, [bmim]BF₄, and multiwalled carbon nanotubes (MWCNTs) were used for improvement of a praseodymium carbon paste ion selective sensor response. [bmim]BF₄ can be a better binder than mineral oils. MWCNTs have a good conductivity which helps the transduction of the signal in carbon paste electrode. The characteristics of these electrodes as potentiometric sensors were evaluated and compared with PVC membrane sensor. The results indicate that potentiometric sensor constructed with ionic liquid shows an increase in performance in terms of Nernstian slope, selectivity, response time, and response stability compared to Pr(III) PVC membrane sensor.     

Chelating ionophore based membrane sensors for copper(II) ions

Acetylacetone, ethylacetoacetate and salicyldehyde, are reported to form chelates with copper of high stability as compared to other metals. Therefore, PVC based membranes of bis[acetylacetonato] Cu(II) (A), bis[ethylacetoacetate] Cu(II) (B) and bis[salicyldehyde] Cu(II) (C) have been investigated as copper(II) selective sensors. The addition of sodium tetraphenylborate and various plasticizers, viz., DOS, TEHP, DOP, DBP and TBP have been found to substantially improve the performance of the sensors. The membranes of various compositions of the three chelates were investigated and it was found that the best performance was obtained for the membrane of composition A (1%): PVC (33%): TBP (65%): NaTPB (1%). The sensor shows a linear potential response to Cu(II) over wide concentration range 2.0 × 10⁻⁶ to 1.0 × 10⁻¹ M (detection limit 0.1 ppm) with Nernstian compliance (29.3 mV decade⁻¹ of activity) between pH 2.6 and 6.0 with a fast response time of 9 s. The potentiometric selectivity coefficient values as determined by match potential method (MPM) indicate excellent selectivity for Cu²⁺ ions over interfering cations. The sensor exhibits adequate shelf life (3 months) with good reproducibility (S.D. ±0.2 mV). The sensor has been used in the potentiometric titration of Cu²⁺ with EDTA. The utility of the sensor has been tested by determining copper in vegetable foliar and multivitamin capsule successfully.     

A perchlorate-selective membrane electrode based on a Cu(II) complex of the ligand 1,4,8,11-tetra(n-octyl)-1,4,8,11-tetraazacyclotetradecane

The new cyclic polyazacycloalkane 1.4,8,11-tetra(n-octyl)-1,4,8,11-tetraazacyclotetradecane (L1) was synthesised and the copper(II) complex [Cu(L1)]2+ characterised. Different electrodes were prepared using the [Cu(L1)]2+ complex as ionophore, PVC as plastic matrix and o-nitrophenyl octyl ether (NPOE), bis(2-ethylhexyl) sebacate (BEHS) or dibutyl phthalate (DBP) as plasticizers. The electrode containing DBP showed a Nernstian response over a wide pH range and a fast response time (ca. 3 s) whereas NPOE and BEHS gave near-Nernstian slopes. Selectivity coefficients for the different anions with respect to perchlorate were calculated. The response of the electrodes basically followed the Hofmeister sequence, suggesting that interaction of the ionophore with the anions is via electrostatic forces rather than due to anion coordination to the axial sites of the square-planar [Cu(L1)]2+ complex.     

Novel Plastic Chromium(III)‐Ion Selective Electrodes Based on Different Ionophoric Species and Plasticizing Solvent Mediators

Different ionophoric species, viz.: 18‐crown‐6 (18C6), dibenzo‐18‐crown‐6 (DB18C6) and calix[6]arene (CAX), as electroactive materials, with 2‐nitrophenyloctylether (2‐NPOE), bis(ethylhexyl)sebacate (DOS), dioctyl phthalate (DOP), and didecyl phthalate (DDP) as plasticizing solvent mediators were used to construct Cr³⁺ selective electrodes in a PVC matrix in the ratio (w/w) PVC: ionophore: plasticizer (60 : 2 : 120). Seven electrodes out of the fabricated 12 electrodes, gave best results in terms of working concentration range (1.0×10^?5?1.0×10^?1 M) with a close to Nernstian slope of 18.5 and a Nernstian slope of 20.0 mV/decade of activity. The usable pH range of the sensors is 4.0–7.0. The detection limit of the selected electrodes is ≤1.0×10^?7 M. The response time of the sensors is 8–35 s, depending on the concentration of Cr³⁺ used. The selectivity coefficient values indicate that the electrodes are highly selective for Cr³⁺ over a number of other cations except Pb²⁺ and Na⁺ (for some electrodes). The electrodes have successfully been used to determine Cr³⁺ in certified and real alloys and in effluents of electroplating shops with a precision as relative standard deviation (RSD)<3%, for each of the proposed Cr³⁺‐ion selective electrodes. The results obtained by the proposed ISEs are in good agreement with the results obtained by direct flame AAS method.     

8-hydroxyquinoline based neutral tripodal ionophore as a copper (II) selective electrode and the effect of remote substitutents on electrode properties

New PVC membrane ion selective electrodes based on 1,3,5-Tris(8-quinolinoxymethyl)-2,4,6-trimethylbenzene (MO8HQ) are reported. The basic sensing material belongs to the group of tripodal ionophores. Also their derivatives prepared by placing suitable substitutents at fifth position of 8-oxine moiety, i.e, 1,3,5-Tris(5-chloro-8-quinolinoxymethyl)-2,4,6-trimethylbenzene (5CHQ), 1,3,5-Tris(5-benzoyl-8-quinolinoxymethyl)-2,4,6-trimethylbenzene (5BHQ) and 1,3,5-Tris[(5-phenylhydroxymethylene)-8-quinolinoxymethyl]-2,4,6-trimethylbenzene (HYD-8HQ) ionophores have also been used to make copper-selective membrane electrodes. Among all the four electrodes, MO8HQ and HYD-8HQ ionophores based electrodes show excellent response towards Cu (II) ions. The electrodes having composition 33% PVC, 4% MO8HQ and 63% dibutyl phthalate (DBP) and 33% PVC, 6% HYD-8HQ, 63% dibutyl phthalate (DBP) exhibit a good Nernstian response to Cu (II) ions in the range of 1.0 × 10⁻⁶ to 1 × 10⁻¹ M. The electrode shows a reasonably fast response time of 15 s. The effect of pH and electrode response is also reported. It shows good selectivity for Cu (II) ions in comparison to heavy metal ions, transition metal ions and for alkali and alkaline earth metal ions. The electrode response and selectivity remains unchanged for at least 5 months. The electrode can be used as an indicator electrode in the potentiometric titration of Cu (II) ions with EDTA.     

Conductometric titration with indicating resistance-III Mechanism of the PVC + Alassion CS (Cationite R-H) + dioctyl phthalate (plasticizer) membrane as indicating resistance

The problem of conductometric acid-base titration in a highly-conducting medium (5M sodium chloride) has been solved by introducing a PVC + Alassion CS + dioctyl phthalate membrane between the two electrodes. The equivalence point is marked by a sudden decrease in conductivity. The membrane (obtained by plasticization at 175 degrees ) functions through the phthalic acid dissolved in the PVC membrane, this acid being formed by decomposition of the dioctyl phthalate by the sulphonic acid groups of the cation-exchanger. In this process the sulphonic acid groups are esterified, but hydrolyse on being treated for 2-3 hr with NaOH, and then increase the conductivity in the membrane.