Lead-selective membrane electrodes based on dithiophenediazacrown ether derivatives

Three double-armed diazacrown ethers with two thiophene side groups, 7,16-dithenyl-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane (DTDC), 7,16-dithenoyl-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane (DTODC), and 7,16-di-(2-thiopheneacetyl)-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane (DTAODC), have been synthesized and used as novel neutral lead(II) ionophores in ion selective electrode applications. The relationship between the molecular structure of these ionophores and electrochemical properties (linear range, response time, selectivity) of the membrane electrode is discussed. The optimum conditions for the preparation of the electrodes are described. The optimized dithenoyldiazacrown had a detection limit of pPb = 5.7, and Nernstian range with slope 29.2 mV decade⁻¹ from pPb = 5.0 to 2.7. Mercury and silver ions are the major interferences. These electrodes are applied to potentiometric titrations of lead(II) ions and show promise for the determination of lead ions in water samples.     

Formation and structures of mercury complexes of 18-membered unsaturated and saturated thiacrown ethers

The complexation of 18-membered unsaturated thiacrown ether, 18-UT-6, with 1 equiv of HgCl(2) in acetone afforded mercury complex Hg(II)(18-UT-6)Cl(2). The complexations of 18-membered saturated thiacrown ether, 18S6, with 1 equiv each of HgCl(2) and CdCl(2) in acetone afforded Hg(II)(18S6)Cl(2) and Cd(II)(18S6)Cl(2), respectively. The crystal structure of Hg(II)(18-UT-6)Cl(2) revealed that the mercury atom was inside the cavity of the macrocycle and the geometry around the mercury atom was an eight-coordinate hexagonal bipyramidal arrangement. ORTEP drawing of Hg(II)(18S6)Cl(2) revealed the existence of the mercury atom outside the cavity of the ring, as well as a polymeric chain structure. (1)H NMR study of Hg(II)(18-UT-6)Cl(2) in acetone-d(6) indicated that the interconversion between free 18-UT-6 and pure complex was slower than the NMR time scale. The titration experiment by (1)H NMR revealed that 18-UT-6 had inclusion selectivity for the number of mercury atoms. The electrochemical behavior of complexes Hg(II)(18-UT-6)Cl(2) and Hg(II)(18S6)Cl(2) was also examined.     

A polymer membrane potentiometric sensor for silver

Four new sulfur-containing compounds based on pyridine, benzene, 1,8-naphthyridine and 1,10-phenanthroline have been synthesized. These molecules have been incorporated into a polymeric matrix as neutral carriers and evaluated as silver sensors. Two of the compounds (pyridine and benzene) show high selectivity for Ag(+). The sensor with the pyridine-based compound, in particular, shows near-Nernstian response and good sensitivity towards Ag(+) with a short response time (<10s), making it ideal for use in flow analysis.     

Serine-selective membrane probe based on immobilized anaerobic bacteria and a potentiometric ammonia gas sensor

A new class of bioselective membrane probes using anaerobic bacteria is introduced with the successful construction of a L-serine-selective probe consisting of Clostridium acidiurici cells coupled to a potentiometric ammonia gas sensor. The intact cells containing the enzyme serine dehydratase are physically immobilized at the electrode surface in conjunction with iron(II) stearate, which is shown to enhance response characteristics. The potential vs. log concentration plot is linear from 1.6 × 10^-2 to 1.8 × 10^-4M serine with an average slope of 54 mV/decade and response times of 3–5 min. Optimal behavior of the probe is retained even in non-deaerated media for at least three days, and significant interference is posed only by L-glutamine. Quantitative conversion of serine is demonstrated over the linear concentration range, suggesting possible analytical or clinical applications for these probes utilizing anaerobic bacteria     

PVC matrix membrane sensor for potentiometric determination of cetylpyridinium chloride.

A novel cetylpyridinium chloride-selective membrane sensor consisting of cetylpyridinium-ferric thiocyanate ion pairs dispersed in a PVC matrix placticized with dioctylphthalate is described. The electrode shows a stable, near-Nernstian response for 1 x 10(-3)-1 x 10(-6) mol l-1 cetylpyridinium chloride (CPC) at 25 degrees C over the pH range 1-6 with a cationic slope of 57.5 +/- 0.4. The lower detection limit is 8 x 10(-7) mol l-1 and the response time is 30-60 s. Selectivity coefficients for CPC relative to a number of interfering substances were investigated. There is negligible interference from many cations, anions and pharmaceutical excipients; however, cetyltrimethylammonim bromide (CTMAB) interfered significantly. The determination of 0.5-350 micrograms/ml of CPC in aqueous solutions shows an average recovery of 98.5% and a mean relative standard deviation of 1.6% at 56.0 micrograms/ml. The direct determination of CPC in Ezafluor mouthwash gave results that compare favorably with those obtained by the British Pharmacopoeia method. Precipitation titrations involving CPC as titrant are monitored with a CP sensor. The CP electrode has been utilized as an end point indicator electrode for the determination of anionic surfactants in some commercial detergents.     

Bifunctional potentiometric sensor based on MoO3 nanorods

A solid-phase film electrode with an ion-sensitive membrane based on MoO₃ nanorods was developed. Depending on the pH of test solution, the proposed electrode can be used as a sensor for measuring the concentration of hydrogen or alkali metal ions. In the range of 1 ≤ pH ≤ 5, the electrode reacts to changes in the concentration of hydrogen ions with an electrode response slope of 54 ± 2 mV/pH. The electrode is selec- tive to alkali metal cations in the concentration ranges of $0 \leqslant pc_{M^ + } \leqslant 4$ for M = Na, K, and Li and $1 \leqslant pc_{M^ + } \leqslant 5$ for M = Rb and Cs and the solution acidity 5 ≤ pH ≤ 13.5 with a nearly theoretical slope. The selectivity coefficients of the electrode to the ions of Na(I), Rb(I), Cs(I), Mg(II), Ca(II), Sr(II), and Ba(II) were determined.     

A potentiometric rhodamine-B based membrane sensor for the selective determination of chromium ions in wastewater.

The construction and performance characteristics of a novel chromate ion-selective membrane sensor are described and used for determining chromium(III) and chromium(VI) ions. The sensor is based on the use of a rhodamine-B chromate ion-associate complex as an electroactive material in a poly(vinyl chloride) membrane plasticized with o-nitrophenyloctyl ether as a solvent mediator. In a phosphate buffer solution of pH 6 - 7, the sensor displays a stable, reproducible and linear potential response over the concentration range of 1 x 10(-1) - 5 x 10(-6) mol l(-1) with an anionic Nernstian slope of 30.8 +/- 0.5 mV decade(-1) and a detection limit of 1 x 10(-6) mol l(-1) Cr(VI). High selectivity for Cr(VI) is offered over many common anions (e.g., I-, Br-, Cl-, IO4-, CN-, acetate, oxalate, citrate, sulfate, phosphate, thiosulfate, selenite, nitrate) and cations (e.g., Ag+, Ca2+, Sr2+, Co2+, Ni2+, Cu2+, Mn2+, Fe2+, Zn2+, Cd2+, Al3+, Cr3+). The sensor is used for determining Cr(VI) and/or Cr(III) ions in separate or mixed solutions after the oxidation of Cr(III) into Cr(VI) with H2O2. As low as 0.2 microg ml(-1) of chromium is determined with a precision of +/-1.2%. The chromium contents of some wastewater samples were accurately assessed, and the results agreed fairly well with data obtained by atomic absorption spectrometry.     

A lead (II) selective PVC membrane potentiometric sensor based on a tetraazamacrocyclic ligand

A polymeric membrane based Pb(II) selective potentiometric sensor was developed by using 1,3,7,9-tetraaza-2,8-dithia-4,10-dimethyl-6,12-diphenylcyclododeca-4,6,10,12-tetraene (TDDDCT) as an electroactive material along with anion excluder sodium tetraphenylborate (NaTPB) and plasticizer dioctylphthalate (DOP). The best performance in terms of slope, concentration range and response time was exhibited by the membrane having TDDDCT:PVC:DOP:NaTPB in the ratio 3:32:62:3 (w/w%). Potentiometric results show that the developed sensor works well in the concentration range 5.0 × 10^?7–1.0 × 10^?1 M with a near Nernstian slope of 29.5 (±0.5) mV decade^?1. The detection limit is down to 2.5 × 10^?7 M. The working pH range of this sensor is 2.8–7.0 and it works well in partially nonaqueous medium up to 25 % (v/v) methanol and ethanol. It exhibits a fast response time of 10 s. Selectivity coefficient values of various interfering ions were determined by the fixed interference method (FIM). The sensor reveals good selectivity for Pb(II) ions over other metal ions investigated. The developed sensor is used in the determination of lead in ‘Eveready battery waste’ and as an indicator electrode in the potentiometric titration of Pb(II) against EDTA.     

Octaethylporphyrin as an ionophore for aluminum potentiometric sensor based on carbon paste electrode

A new sensor to quantitatively sense aluminum in real sample conditions is presented that uses the potentiometric ion selective electrodes. Aluminum is a cation that plays an important role in the environmental process. This approach is proposed to determine aluminum levels in real samples in the required range (10^?6–10^?2 M). Carbon paste electrode (CPE) is introduced here as a potentiometric sensor to measure free concentration of aluminum ion. Octaethylporphyrin (OEP) acts as a selective aluminum recognition agent in the CPE. The suitable selectivity coefficient is obtained for the CPEs compare to interfering cation. The Nernstian slope and detection limit are achieved 18.4 mV/decade and 2.5 × 10^?6 M Al³⁺, respectively. Finally, the proposed method is applied to determine aluminum concentration in real water samples and the result of this method is in agreement with the result of atomic absorption spectroscopy (AAS).     

Novel membrane potentiometric sulfate ion sensor based on zinc-phthalocyanine for the quick determination of trace amounts of sulfate.

Poly(vinyl chloride) (PVC) based membranes of zinc-phthalocyanine (ZPC) with hexadecyltrimethylammonium bromide (HTAB) as a cation excluder, and dibutyl phthalate (DBP) and benzyl acetate (BA) as plasticizing solvent mediators were prepared and investigated as a SO4(2-) selective electrode. The best performance was observed with a membrane having a composition of ZPC-PVC-HTAB-BA in a ratio of 5%:32%:3%:60%, which works well over a wide concentration range (1.0 x 10(-2) - 1.0 x 10(-6) M) with a Nemstian slope of -29.2 mV per decade of activity, between the pH values of 2.0 to 7.0. This sensor shows a very fast response time of 10 s, and can be used over a period of 2 months with good reproducibility. The proposed sensor displays excellent selectivity for SO4(2-) over a large number of common inorganic anions. The sensor has been successfully applied for the direct and indirect determination of sulfate and zinc in zinc sulfate tablets, respectively. It was also used as an indicator electrode in the potentiometric titration of sulfate ions with barium ions.     

Polymeric membrane sensor for potentiometric determination of vanadyl ions

In this research, new electrodes were prepared by incorporating a new calix[4]arene derivative into a plasticized poly(vinyl chloride) matrix. Calibration plots with Nernstian slopes (29.9 ± 1.1 mV/decade) for vanadyl ion were observed over a linear range of about four decades of concentration (1.0 × 10⁻⁵ to 1.0 × 10⁻¹ mol dm⁻³, at 25 °C). This electrode revealed a lower limit of detection of 3.9 × 10⁻⁶ mol dm⁻³. Conductometric data showed the relatively strong interaction between calix[4]arene and vanadyl ions. The results show that this electrode can be used in acetonitril and methanol media until 10% (v/v) concentration without interference. It has a short response time and can be used for more than two months without any considerable divergence in the potentials. The influence of membrane composition, the pH of the test solution, and the interfering ions on the electrode performance was investigated. The effect of temperature on the electrode response showed that the temperature higher than 50 °C deteriorates the electrode performance. The isothermal temperature coefficient of this electrode amounted to 0.0015 V °C⁻¹. The results of application show that the electrode can be used successfully in present Cr³⁺ and Fe³⁺.     

A novel uranyl membrane sensor with potentiometric anionic response

A novel potentiometric uranyl membrane sensor with a divalent anionic response is developed, characterized and used for determination of uranyl ion. The sensor incorporates triethylenetetramine (TETA) as an ionophore in poly(vinyl chloride) matrix membrane (PVC) plasticized with o-nitrophenyloctyl ether (o-NPOE). In strong sulphate test solutions, UO₂²⁺ ion forms a highly stable [UO₂(SO₄)₂]²⁻ anion, extractable in TETA as {(2TETAH)²⁺ [UO₂(SO₄)₂]²⁻} complex. Formation of the complex is confirmed and characterized by elemental analysis, mass spectrometry and infrared spectrometry. Sensor based on this system displays at pH 2.5-3.8 a linear response over the concentration range of 1.0 × 10⁻¹-3.5 × 10⁻⁵ mol l⁻¹ uranium with a near-Nernstian calibration slope of −26.5 ± 0.3 mV decade⁻¹. The lower limit of detection is ∼5 μg ml⁻¹, the lifetime is 12 weeks and negligible interferences are caused by most common cations. Validation of the assay method reveals excellent performance characteristics in terms of sensitivity, selectivity, fast response and potential stability. The sensor is used for the determination of 0.01-7.09 wt% uranium in naturally occurring and certified ore samples. The results show an average recovery of 97.6% and compare fairly well with data obtained using X-ray fluorescence technique.     

Flow injection analysis of sulfite ion with a potentiometric titanium phosphate-epoxy based membrane sensor

A novel pH sensor suitable for use in both aqueous and non-aqueous mediums is reported. The sensor is derived from polymer modified electrode obtained from electrochemical polymerisation of aniline in dry acetonitrile containing 0.5 M tetraphenyl borate at 2.0 V versus Ag/AgCl. The light yellow colour polymer modified electrode obtained under the present experimental condition has been characterised by scanning electron microscopy (SEM). The pH sensing of polymer modified electrode in both aqueous and non-aqueous mediums is examined and reported. As the typical examples, we used weak acid (acetic acid) and weak base (ammonium hydroxide) as analytes. The acetic acid is analysed in both aqueous and dry acetonitrile whereas ammonium hydroxide is analysed only in aqueous medium. The analysis in aqueous medium is conducted in 1 mM Tris-HCl buffer pH 7.0 and also in 0.1 M KCl. The slope of pH sensing is calculated from the data recorded in typical buffers and found to be approximately 86 mV per pH. The application of polymer modified electrode for the construction of urea biosensor is described based on immobilised urease within poly vinyl alcohol (PVA) matrix and also within organically modified sol-gel glass on the surface of polymer-modified electrode. The new urea sensor has shown maximum response of 160 mV at 25 degrees C with a lowest detection limit of 20 muM. The performance of new pH sensor and urea sensor has been studied and reported in this communication.     

PVC matrix membrane sensor for potentiometric determination of dodecylsulfate

The construction and performance characteristics of a new potentiometric PVC membrane sensor for the determination of sodium dodecyl sulfate (SDS) are described. The sensor was based on the use of an N-cetyl-N,N,N trimethyl ammonium (CTA) dodecyl sulfate (DS) ion pair as ion exchange sites in PVC matrix in the presence of o-nitrophenyl octylether as plasticiser. The sensor exhibited a fast, stable, and near-Nernstian response for SDS over the concentration range of 1 × 10^?3 to 10^?6 M at 25°C and the pH range 4–8.5 with anionic slope of 52.5 ± 0.5 mV decade^?1. The lower detection limit was 3 × 10^?6 M, and the response time was 25 s. Selectivity coefficients of SDS with respect to a number of different species were investigated. There were negligible interferences caused by most of the investigated anions. The determination of 1.0–280.0 µg mL^?1 of SDS in aqueous solutions showed an average recovery of 99.1%, and the mean relative standard deviation was 1.4 at 100 µg mL^?1. The results obtained in the determination of SDS in liquid soap, water and in some pharmaceutical preparations compared favourably with those obtained by the Methylene Blue active substance method (MBAS). In the present investigation, the DS sensor has been used as an end-point indicator electrode for some precipitation titration reactions, e.g. titration of SDS with CTMABr and cetylpyridinium chloride with SDS.     

Lead-selective poly(vinyl chloride) membrane electrodes based on acyclic dibenzopolyether diamides

Lipophilic acyclic dibenzopolyether diamides, 12 kinds, have been designed to prepare solvent polymeric membrane ion-selective electrodes (ISEs) for Pb(2+). The ionophores include 1,5-bis[2-(N,N-dialkylcarbamoylmethoxy)phenoxy]-3-oxapentanes1-4, 1,5-bis[2-(N,N-dialkylcarbamoylpentadecyloxy)phenoxy]-3-oxapentanes 5-8, and 1,2-bis[2-(2'-N,N-dialkylcarbamoylpentadecyloxy)phenoxy]ethanes 9-12. Linear response concentration range of the ISE based on 9 is 3 x 10(-2) - 1 x 10(-6) M of Pb(2+) (average slope = 28.5 mV decade(-1)). Potentiometric selectivities of the ISEs based on 1-12 for Pb(2+) over other heavy metal cations, alkali metal cations, and alkaline earth metal cations have been assessed. These ISEs exhibit remarkably high selectivities for Pb(2+) relative to heavy metal cations, such as Cu(2+), Fe(2+), and Ni(2+), the selectivity coefficients (K(Pot)(Pb,Cu)) being 5 x 10(-5) - 6 x 10(-5) for 1-4 and ca. 6 x 10(-4) for 9. For the Pb(2+) selectivities over alkali metal cations, such as Na(+) and K(+), 9 which has an ethylene glycol spacer and a N,N-diethyl group is superior to other dibenzopolyether diamide ionophores 1-8 and 10-12.     

Lead-selective poly(vinyl choride) membrane electrodes based on heterocyclic thiocarboxylic acid

Heterocyclic thiocarboxylic acids have been designed to prepare polymeric membrane ion-selective electrode (ISE) for Pb²⁺. Construction, response characteristic and application of the lead ISEs are investigated. Better results have been obtained with membranes containing ligands L1∼L3 with bis(2-ethylhexyl) sebacate (DOS) as a plasticizer. Ionophores L1∼L3 are [(4,6-dimethyl-2-pyrimidinyl) thio] acetic acid (L1), (1,3,4-thiadiazole-2,5-diyldithio) diacetic acid (L2) and (1,3,4-thiadiazole-2,5-diyldithio) dipropionic acid (L3). The optimum electrodes have the composition of L1 (1.6): PVC (32.7): DOS (65.3): KT _p ClPB (0.4) (w/w), L2 (1.0): PVC (32.8): DOS (66.0): KT _p ClPB (0.2) (w/w), and L3 (1.0): PVC (32.7): DOS (65.4): KT _p ClPB (0.9) (w/w). The optimized membrane electrodes work well over a wide range of concentrations (1.0 × 10⁻⁵ ∼1.0 × 10⁻² M, 1.0 × 10⁻⁶ ∼1.0 × 10⁻² M, and 1.0 × 10⁻⁶ ∼1.0 × 10⁻² M) with the response slope of 27.4, 30.1 and 29.2 mV/decade, respectively. Potentiometric selectivities of the ISEs based on L1 ∼ L3 for Pb²⁺ over other interfering ions are determined with the fix interference method. The electrodes display good selectivity over a number of alkali, alkaline earth, transition and heavy metal ions. The lifetime of the electrodes is about 2 months and their response time is 20 s. Applications of these electrodes for the determination of lead in real samples and as indicator electrodes for potentiometric titration of Na₂SO₄ using Pb²⁺ solution are reported.     

Novel potentiometric sensor for monitoring beryllium based on naphto-9-crown-3.

A novel poly(vinyl chloride) (PVC) membrane electrode based on naphto-9-crown-3 was prepared and tested for the selective detection of beryllium ions. A suitable lipophilicity of the carrier and appropriate coordination ability were found to be essential for designing an electrode with good response characteristics. A PVC membrane with 9% naphtho-9-crown-3 carrier, 58% o-NPOE plasticizer, 3% tetraphenylborate anionic excluder and 30% poly(vinyl chloride) satisfied these requirements. The proposed sensor displayed a linear response to beryllium over a wide concentration range of 1.0 x 10(-1)-8.0 x 10(-6) M with a Nernstian slope of 29.5 mV per decade. The electrode showed very short response time (<15 s) and could be used in the pH range 3.5-9.0. The selectivity coefficient for alkali, alkaline earth, transition and heavy metal ions was smaller than 4.0 x 10(-4). The sensor was successfully used as an indicator electrode in the potentiometric titration of Be2+ with EDTA. The proposed Be(II) sensor was also used for the determination of Be2+ ions in binary mixtures.     

Determination of betamethasone sodium phosphate in pharmaceuticals by potentiometric membrane sensor based on its lidocaine ion pair

Betamethasone sodium phosphate (BMNaP) has been employed as an electroactive material in the design of an ion-selective electrode (ISE). The electrode incorporates PVC membrane with betamethasone sodium phosphate-lidocaine ion pair complex. The influences of membrane composition, temperature, pH of the test solution, and the interfering ions on the electrode performance were investigated. The sensor exhibits a Nernstian response for betamethasone sodium phosphate ions over a relatively wide concentration range (1.0 × 10^?1 to 1.0 × 10^?5 M) with a slope of 28.4 ± 0.9 mV per decade at 25°C. It can be used in the pH range 4.0–10.0. The isothermal temperature coefficient of this electrode amounted to ?0.0008 V/°C. The membrane sensor was successfully applied to the determination of betamethasone sodium phosphate in pharmaceutical products.     

A novel ferroin membrane sensor for potentiometric determination of iron

A novel potentiometric approach for both batch and flow injection determination of iron(II) and/or iron(III) is described. It is based on the formation and monitoring of ferroin with a PVC membrane sensor containing ferroin-TPB as an electroactive component plasticized with 2-nitrophenyl phenyl ether. The sensor exhibits fast Nernstian response for ferroin with a cationic calibration slope of 30 +/- 0.2 mV/concentration decade down to 4 x 10(-7)M ferroin (0.03 ppm Fe) at pH 3-9. Interferences from common inorganic cations are negligible or can be eliminated by a pretreatment with DDC. The ferroin sensor was successfully applied to the determination of iron contents in water, alloys, rocks and pharmaceuticals. The results show good correlation with data obtained by the standard spectrophotometric ferroin method, the coefficient of correlation is better than 0.7%.