Potentiometric Response Characteristics Research Articles

All-solid-state hydrogen sensing microelectrodes based on novel PPy[3,3′-Co(1,2-C 2B 9H 11) 2] as a solid internal contact

Planar all-solid-state hydrogen sensing microelectrodes have been constructed and investigated. A novel conductive polymer, polypyrrole (PPy) doped with cobaltabis(dicarbollide) ions ([3,3′-Co(1,2-C 2B 9H 11) 2] −), thin film was galvanostatically grown over a solid substrate (Pt) and acted as an internal solid contact layer between the solid surface (Pt) and the polymeric sensitive membrane. The potentiometric response characteristics of this new kind of microelectrode based on tri- n-dodecylamine (TDDA) ionophore were evaluated. They exhibited excellent selectivity for the primary ion and a linear response over the pH range 3.5–11.0 with a slope of 52 ± 2 mV decade − 1 . The selectivity properties have been examined. The results obtained were comparable to that of a conventional ion-selective electrode (ISE) based on the same ionophore.

A zinc-selective electrode based on N, N′-bis(acetylacetone)ethylenediimine

The potentiometric response characteristics of electrodes based on N, N′-bis(acetylacetone)ethylenediimine ( I) in poly(vinyl chloride) (PVC) combined with an anion localizing agent (sodium tetraphenyl borate, NaTPB) and solvent mediators, viz. o-nitrophenyl octyl ether (NPOE), dibutyl (butyl) phosphonate (DBBP), tri- n-butyl phosphate (TBP) and chloronaphthalene (CN) were investigated. The best result for Zn 2+-sensing was obtained for the electrode membrane of the composition of I:PVC:NaTPB:NPOE = 5:100:6:200, where the electrode had a Nernstian response (30.0 mV/decade of Zn 2+ activity) to Zn 2+ within the concentration range of 1.0 × 10 −6 to 1.0 × 10 −1 M. The operational pH range of the electrode was 3.2–7.1. Selectivity characteristic of the proposed electrode was also assessed by calculating K A , B Pot with a fixed interference method. The sensor has been successfully used in real sample analysis and also in the potentiometric titration of zinc ions with EDTA.

A copper-selective electrode based on bis(acetylacetone)propylenediimine

The potentiometric response characteristics of Cu 2+-selective electrodes based on bis(acetylacetone)propylenediimine ( I) combined with anion localizing agent (sodium tetraphenyl borate (NaTPB)) and solvent mediators (dibutyl butyl phosphonate (DBBP), tri- n-butyl phosphate (TBP) and chloronaphthalene (CN)) were investigated. The best results for Cu 2+ sensing was obtained for the electrode membrane containing PVC, I, DBBP and NaTPB in composition 5:100:200:6 ( I:PVC:DBBP:NaTPB) (w/w; mg), where the electrode had a Nernstian response (30.0 mV/decade) to Cu 2+ within the concentration range 1.0 × 10 −5 to 1.0 × 10 −1 M and detection limit of 0.5 ppm. The operational pH range of the electrode was 3.3–7.0. Selectivity characteristic of the proposed electrode was also assessed by calculating K A , B Pot using fixed interference method matched potential method. The sensor has been successfully used in the potentiometric titration of copper ions with EDTA.

Rhodium(II) Phthalocyanine as a Selective Carrier in Thiocyanate‐Selective Membrane Electrode

An anion‐selective electrode based on rhodium(II) phthalocyanine (RhPc) as a neutral carrier is reported. The prepared electrode displays an anti‐Hofmeister behavior with a high selectivity for thiocyanate. The potentiometric response characteristics and selectivities of the membrane electrodes with various ratios of cationic additive to ion‐carrier indicate that the observed potentiometric response is based on the formation of a 1:1 complex between RhPc and thiocyanate as an axial ligand. The membrane electrodes containing ∼60 mol percent of cationic additive (relative to ionophore) exhibit a near‐Nernstian response in a concentration range of thiocyanate between 1×10−6 M to 1×10−1 M, a detection limit of 7.9×10−7 M, and a slope of −56.3 mV/decade in pH 6.0 using 0.1 M phosphate buffer solution. In comparison to the previously reported CoPc‐based membrane electrode, the prepared electrode showed better selectivity for thiocyanate over the relatively more hard anions, such as SO4 2−, H2PO4 −, HCO3 −, NO3 −, F−, Cl−, C2O4 2− and OAc−. This preference in response is assisted by the softness property of Rh2+ in the center of RhPc. The prepared electrode revealed a fast response time, sub‐micromolar detection limit, and a long‐time stability of more than 2 months (with less than 3% decrease in the slope of the potentiometric response). Application of the electrode with the optimum composition for determination of thiocyanate in pharmaceutical preparations (erythromycin thiocyanate) and human urine samples is reported. The electrode is also applied as an indicator electrode in potentiometric titration of milimolar solutions of thiocyanate and silver nitrate.

Effects of ion-carrier substituents on the potentiometric-response characteristics in anion-selective membrane electrodes based on iron porphyrins.

The potentiometric response characteristics with respect to salicylate anion of several membrane electrodes based on iron(III) tetraphenylporphyrin chloride (FeTPPCl) and derivatives with electrophilic and nucleophilic substituents, incorporated into plasticized polyvinylchloride (PVC) membranes were investigated. Complexes tetraphenyl porphyrin iron(III) chloride (FeTPPCl; A), tetrakis (4-methoxyphenyl) porphyrin iron(III) chloride (Fe(TOCH3PP)Cl; B), tetrakis (2,6-dichlorophenyl) porphyrin iron(III) chloride (Fe(TDClPP)Cl; C), tetrakis (4-nitrophenyl) porphyrin iron(III) chloride (Fe(TNO2PP)Cl; D), and tetrakis (pentafluorophenyl) porphyrin iron(III) chloride (Fe(TPFPP)Cl; E) were used as anion carriers in the membrane electrodes. The sensitivity, working range, detection limit, response mechanism, and selectivity of the membrane sensor toward interference shows a considerable dependence on the type of carrier substituent and the pH value of the sample solution. Potentiometric investigations in solutions of various pH show that the carrier complex containing fluoro substituents (E), which have very strong electron-accepting properties and a high ability to form hydrogen bonds, is capable of serving as a positively charged ionophore. Some other ionophores are capable of serving as both charged and neutral carriers under different conditions. The electrodes prepared in this work show super-Nernstian slopes with respect to salicylate concentration, which tend to a Nernstian response (slope near to -59 mV decade-1) upon an increase of the pH of the test solution. The results of UV/Vis absorption spectroscopy are used for interpretation of the formation of an oxene complex between salicylate and iron porphyrins.

Organic tin compounds combined with anionic additives—an ionophore system leading to a phosphate ion-selective electrode?

The potentiometric response characteristics of electrodes based on organic trialkyl/aryl-tin compounds combined with various amounts of anionic additive (NaTFPB) were investigated in 0.1 M bis-Tris–H 2SO 4 buffer solution at pH 7.0. The best result for phosphate sensing was obtained for the electrode membrane containing tributyltin chloride and 25 mol% NaTFPB, where the electrode exhibits high selectivity towards phosphate anions with a slope of −60 mV per decade. It was demonstrated that the interference from more lipophilic anions is drastically suppressed ( log K ij pot , i=H 2PO 4 −: salicylate, 0.5; SCN −, −0.8; ClO 4 −, −2.3) under this optimized measurement conditions.

Potentiometric response characteristics of polycation-sensitive membrane electrodes toward poly(amidoamine) and poly(propylenimine) dendrimers.

The potentiometric response characteristics of polycation-sensitive membrane electrodes toward two classes of polycationic dendrimers are examined. Using appropriately formulated polymer membrane electrodes composed of a dinonylnaphthalenesulfonate (DNNS) salt in a plasticized polyurethane matrix, it is shown that poly(amidoamine) (PAMAM) and poly(propylenimine) (PPI) dendrimers are readily detected at submicrogram per milliliter levels via a nonequilibrium response mechanism. The relationship between the total EMF response (at equilibrium) and the specific dendrimer structure is also examined. For both the PAMAM and PPI species, it is shown that the total EMF response does not change significantly with dendrimer generation number; however, the nonequilibrium analytically useful response curves are shifted to higher mass concentrations as the generation number is increased. The relative contributions of the terminal primary amines and the interior tertiary amines of the dendrimers to the observed EMF response are investigated by synthesis of various dendrimer derivatives (acetylated, quaternized, etc.). By comparing the total EMF responses for these derivatives as a function of sample pH, it is demonstrated that the lipophilic cation exchanger (DNNS) within the membrane phase can likely interact electrostatically with both protonated forms of the terminal primary amines and interior tertiary amines of the dendrimer structures. The practical application of the nonequilibrium potentiometric detection of dendrimers for monitoring their interaction with DNA is also demonstrated.

Novel lanthanum(III) membrane sensor based on a new N-S Schiff’s base

A novel lanthanum(III) sensor based on bis(thiophenal)phenylen-1,3-diamine (TPD) is described. The sensor was prepared by incorporating the TPD into plasticized PVC membrane. The sensor displays high selectivity for lanthanum with respect to many common alkali, alkaline earth, transition and heavy metal ions. The effect of membrane composition and pH and influence of additive anionic on the response properties of were investigated. The sensor with 35% PVC, 54% solvent mediator, 8% ionophore and 3% anionic additive, shows the best potentiometric response characteristics. It displays a Nernstian behavior (19.6 mV per decade) over the concentration range 1.0×10 −7 to 1.0×10 −1 M. The detection limit of the electrode is 2.0×10 −8 M (∼3.0 ng/ml). The response time of the electrode is very fast (10 s) in whole concentration range. The sensor can be used in the pH range 3.5–9.5 for at least 2 months. The membrane sensor was used as an indicator electrode in potentiometric titration of lanthanum ions with EDTA. It was successfully applied in determination of fluoride ions in mouth wash preparations.

Highly selective thiocyanate electrode based on bis-bebzoin-semitriethylenetetraamine binuclear copper(II) complex as neutral carrier

A novel selective thiocyanate PVC membrane electrode based on bis-bebzoin-semitriethylenetetraamine binuclear copper(II) [Cu(II) 2–BBSTA] as neutral carrier is reported, which displays an anti-Hofmeister selectivity sequence in following order: SCN − > ClO 4 − > I − >Sal − >SO 3 2− >NO 3 − > H 2PO 4 − > Cl − >NO 2 − > SO 4 2−. The electrode exhibits Nernstian potential linear range to thiocyanate from 1.0 × 10 −1 to 9.0 × 10 −7 mol/l with a detection limit 7.0 × 10 −7 mol/l and a slope of −57.0 mV/decade in pH 5.0 of phosphorate buffer solution at 25 °C. The response mechanism is discussed in view of the AC impedance technique and the UV spectroscopy technique. From comparison of potentiometric response characteristics between the binuclear metallic complex copper(II) [Cu(II) 2–BBSTA] and mononuclear copper(II) metallic complex [Cu(II)–BBSDA], an enhanced response towards thiocyanate from the electrode based on binuclear metallic complex copper (II) [Cu(II) 2–BBSTA] was observed. The electrode based on binuclear copper(II) compound was used to determine the thiocyanate content in waste water with satisfactory results.

Silver ion-selective electrodes employing Schiff base p- tert-butyl calix[4]arene derivatives as neutral carriers

The potentiometric response characteristics and selectivity properties of poly(vinylchloride) (PVC) matrix membrane ion-selective electrodes for silver(I) ion, based on Schiff base p- tert-butyl calix[4]arene derivatives containing N and O as binding sites, were examined. These derivatives proves to work well with silver ions and corresponding electrodes display an excellent response to this ion. These electrodes works well over wide range of concentration ( 1.0×10 −5 to 1.0×10 −1 M) with a Nernstian slope. The electrodes have a fast response time of 20 s and operates in the wide pH range. These calix[4]arene derivatives, each showed excellent selectivities in ISE membrane electrodes with log K Ag, M pot around −4.5 against some of the alkali, alkaline and transition metals, even against the strongest interferent, Hg 2+ ions, the value was around −3.0. These silver(I) ion-selective electrodes were used as an indicator electrode for potentiometric titration of silver(I) using standard solution of sodium chloride, a sharp potential change occur at the end point. These ISEs were also used to determine low concentration of silver(I) ion in partially non-aqueous medium.

A mercury(II) ion-selective electrode based on neutral salicylaldehyde thiosemicarbazone

A new ion-selective PVC membrane electrode based on salicylaldehyde thiosemicarbazone as an ionophore is developed successfully as sensor for mercury(II) ions. The electrode shows excellent potentiometric response characteristics and displays a linear log[Hg 2+] versus EMF response over a wide concentration range of 1.778×10 −6–1.0×10 −1 M with Nernstian slope of 29 mV per decade with the detection limit of 1.0×10 −6 M. The response time of the electrode is less than 30 s and the membrane electrode operates well in the pH range of 1.0–3.0. The lifetime of the sensor is about 2 months. The electrode shows better selectivity towards Hg 2+ ions in comparison with the alkali, alkaline and some heavy metal ions; most of these metal ions do not show significant interference ( K Pot Hg, M values of the order of 10 −3–10 −4). The present sensor showed comparable or even better performance vis-à-vis similar PVC based ion-selective electrodes reported in literature. The sensor was also applied as an indicator electrode for potentiometric titration of Hg 2+ions with I − and Cr 2O 7 2−.

Cesium ion selective electrode based on calix[4]crown ether–ester

The potentiometric response characteristics of cesium ion selective PVC membrane electrode employing calix[4]crown ether–ester as an ionophore were investigated. The electrode exhibit a good response for cesium ion over wide concentration range of 5.0×10 −6–1.0×10 −1 M with a Nernstian slope of 59 mV per decade. The detection limit of electrode is 5.0×10 −6 M. The electrode was found to have selectivity for cesium ion over alkali, alkaline and transition metals. The response time of the electrode is less than 20 s and can be used for more than 4 months without observing any divergence in potentiometric response. The electrode response was stable over wide pH range.

Improving the Blood Compatibility of Ion-Selective Electrodes by Employing Poly(MPC-co-BMA), a Copolymer Containing Phosphorylcholine, as a Membrane Coating

The hydrogelpoly(2-methacryloyloxyethylphosphorylcholine-co-butyl methacrylate), or poly(MPC-co-BMA), was used as a coating for polyurethane- and poly(vinyl chloride)-based membranes to develop ion-selective electrodes (ISEs) with enhanced blood compatibility. Adverse interactions of poly(MPC-co-BMA) with blood were diminished due to the phosphorylcholine functionalities of the hydrogel, which mimic the phospholipid polar groups present on the surface of many cell membranes. As demonstrated by immunostaining, hydrogel-coated PVC membranes soaked in platelet-rich plasma showed less adhesion and activation of platelets than uncoated PVC membranes, indicating an improvement in biocompatibility owing to the hydrogel. Furthermore, little differences in the potentiometric response characteristics, e.g., slope, detection limit, and selectivity, of ISEs employing uncoated and coated membranes were observed.

Continuous flow analysis of iron in zinc electrowinning electrolyte using an iron chalcogenide glass ion-selective electrode: Part I. Synthetic media

It is shown that the iron(III) chalcogenide glass membrane ion-selective electrode (ISE) can be calibrated in continuous flow analysis (CFA) using acidified iron(III) nitrate standards, yielding a 60±3 mV per decade change in activity of Fe 3+ response in the range 10 −7–10 −2 M total iron(III). Extended ageing of the iron(III) ISE in 2 M zinc(II) sulphate did not alter the potentiometric response characteristics of the electrode. Furthermore, electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy in the presence and absence of zinc(II) sulphate failed to detect a zinc(II) interference on the iron(III) ISE. CFA/ISE determined activities of Fe 3+ in synthetic zinc electrolyte containing 2×10 −3–2×10 −1 M total iron(III) yielded results falling within ±0.2 log aFe 3+ unit of the corresponding iron speciation data calculated using the minteqa2 program.

Salicylate-selective membrane electrodes based on Sn(IV)- and OMo(V)-porphyrins: differences in response mechanism and analytical performance

The potentiometric response characteristics (slope and selectivity) of salicylate-selective electrodes based on Sn(IV) and OMo(V) (oxomolybdenum) tetraphenylporphyrins (TPP) in o-nitrophenyloctylether plasticized poly(vinyl chloride) membranes are compared. Super-Nernstian salicylate responses (slopes>−100 mV decade −1) are observed for membranes doped with Sn(IV)[TPP]Cl 2 and 10–30 mol% of a lipophilic tetraphenylborate derivative (sodium bis[trifluoromethyl]phenylborate, NaTFPB). The borate derivative is required to optimize potentiometric selectivity for salicylate over other anions in accordance with existing theory for charged carrier type anion selective ionophores. The super-Nernstian response of Sn(IV) porphyrin doped membranes is shown, via UV–vis spectroscopy, to result from spontaneous formation of hydroxide ion bridged porphyrin dimers in the membrane phase, which are converted to monomeric porphyrin upon increasing the concentration of salicylate in the sample solution. In contrast, the salicylate response of the membranes doped with OMo(V)[TPP]OEt are Nernstian (−56 to 60 mV decade −1), even in the presence of added borate derivative to optimize salicylate selectivity. UV–vis spectroscopic studies of the membranes doped with the molybdenum species confirm the absence of dimer formation, which correlates well with the conventional Nernstian response behavior of such membranes. Electrodes formulated with the optimized membranes containing OMo(V)[TPP]OEt and the borate derivative (10–35 mol%) are shown to exhibit high selectivity for salicylate over many anions, even lipophilic anions such as perchlorate (log K pot≤−2.5).

PORPHYRIN DIMER AS NEUTRAL IONOPHORE FOR A BERBERINE-SENSITIVE POTENTIOMETRIC SENSOR

The synthesis of a dimer of porphyrin linked by flexible alkoxyl chains and its application as neutral ionophore for a berberine-sensitive potentiometric sensor were described. The porphyrin dimer based sensor shows a linear response towards berberine in the range 1.2 × 10−7–5.0 ×10−3 mol L−1, with a pH range from 3.7 to 11.2, a fast response time of 10 s and a slope of 65.5 ± 2.5 mV/dec. The proposed electrode exhibits different selectivity behavior compared with the electrode based on classical cation exchanger. As an electroactive material, porphyrin dimer shows better potentiometric response characteristics comparing to porphyrin monomer or metalloporphyrin. The effects of solvent mediator have been studied and the experimental conditions optimized. The interaction between BE+ and porphyrin dimer was investigated using UV-VIS spectrophotometry. The electrode can be used in the direct assay of BE in pharmaceutical preparations with satisfactory results.

Salicylate-selective electrodes based on AI(III) and Sn(IV) salophens

New salicylate-selective electrodes based on aluminum-(III) and tin(IV) salophens are described. The electrodes were prepared by incorporating the ionophores into plasticized poly(vinyl chloride) (PVC) membranes, which were directly coated on the surface of graphite electrodes. These novel electrodes display high selectivity for salicylate with respect to many common inorganic and organic anions. The influence of membrane composition and pH and the effect of lipophilic cationic and anionic additives on the response properties of the electrodes were investigated. The electrode based on aluminum salophen, with 32% PVC, 65.8% plasticizer, and 2.2% ionophore, shows the best potentiometric response characteristics and displays a linear log [Sal-] vs EMF response over the concentration range 1 x 10(-6) - 1 x 10(-1) M in phosphate buffer solutions of pH 7.0, with a Nernstian slope of -59.2 mV/decade of salicylate concentration. Highest selectivity was observed for the membrane incorporating 38.8% PVC, 57.3% plasticizer, 2.6% Sn(salophen), and 1.3% sodium tetraphenylborate. The electrodes exhibit fast response times and micromolar detection limits (approximately 1 x 10(-6) M salicylate) and could be used over a wide pH range of 3-8. Applications of the electrodes for determination of salicylate in pharmaceutical preparations and biological samples are reported.

A novel ethacrynic acid sensor based on a lanthanide porphyrin complex in a PVC matrix

Lanthanide porphyrin complexes synthesized by a solid state method were used to prepare a novel ethacrynic acid (EA) sensor. The sensor, based on pentane-2,4-dionato(meso-tetraphenylporphinato)terbium [TbTPP(acac)] with an optimized membrane composition, exhibits a Nernstian response to EA- ion in the concentration range 7.4 x 10(-6)-1.0 x 10(-1) mol l-1 with a pH range from 3.2 to 6.8 and a fast response time of 30 s. The electrode shows improved selectivity towards EA- ion with respect to common co-existing ions compared with the previously reported EA sensor. As electroactive materials, lanthanide porphyrin complexes show better potentiometric response characteristics than copper porphyrin complexes. The effect of solvent mediators and lipophilic ion additives was studied and the experimental conditions were optimized. The electrode was applied to the determination of EA in human urine samples with satisfactory results.

Bismetalloporphyrin-based ISE sensitive to fluoroborate.

Several mu-oxo-bismetalloporphyrin complexes were synthesized for preparing fluoroborate sensors. The electrode based on mu-oxo-bis[tetra(p-chlorophenyl)porphinatomanganese(III)] with an optimized membrane composition shows a potentiometric response towards fluoroborate ion over the concentration range from 4.3 x 10(-7) to 1.0 x 10(-1) mol l-1 with a Nernstian slope, a wide working pH range from 5.5 to 12.0 and a fast response time of 30 s. The electrode shows anti-Hofmeister selectivity towards BF4- with respect to common co-existing ions, which is an improvement over methods reported so far. As electroactive materials, several mu-oxo-bismetalloporphyrins with different substituents on the benzene rings were compared for potentiometric response characteristics. The interaction between BF4- and bismetalloporphyrin was investigated using UV/VIS spectrophotometry. The electrode was applied to the determination of fluoroborate in electroplating solutions.

Pentacoordinate organotin complexes as neutral carriers for salicylate-selective PVC membrane electrodes

Selectivity properties are established for three new electrodes prepared by incorporating three pentacoordinate organotin(IV) complexes, mono(2,4-pentanedionato- o, o′) tri(phenylmethyl)tin (DMTBS), mono(benzoylacetonato- o, o′) tri(phenylmethyl)tin (MPTBS) and mono(dibenzoylmethanato- o, o′) tri(phenylmethyl)tin (DPTBS) into plasticized PVC membranes. These electrodes exhibit linear response to salicylate and an anti-Hofmeister selectivity pattern with high specificity for salicylate over many common anions. The results show that the potentiometric response characteristics are related to the structure of organic ligands. The detection limit and the slope of the electrodes based on these pentacoordinate organotin complexes exhibit a tendency to decrease as the substituent in organic ligands changes from a methyl group to a phenyl group. Electrodes prepared with DMTBS have the best detection limit and the highest degree of selectivity and sensitivity for salicylate. The response mechanism is also investigated by use of a.c. impedance and i.r. spectroscopic techniques.