Hydroxy-thioxanthones as suitable neutral ionophores for the preparation of PVC-membrane potentiometric sensors for Al(III) ion.

The complexation of five recently synthesized hydroxy-thioxanthone derivatives with Al3+ ion was studied in a methanol solution spectrophotometrically, and the stepwise formation constants of the resulting 1:1 and 2:1 (ligand-to-metal) complexes were evaluated. The suitability of the thioxanthone derivatives as neutral ionophores for the preparation of a new Al3+ ion-selective PVC-membrane electrode was investigated, and 1-hydroxy-3-methyl-thiocanthone was selected as the best compound for this purpose. The prepared electrode exhibits a Nernstian response for Al3+ ions over a wide concentration range (2.0 x 10(-2) to 2.0 x 10(-6) M), with a limit of detection of 1.0 x 10(-6) M. It has a very fast response time of about 5 s and can be used for at least 3 months without any considerable divergence in the potentials. The proposed membrane sensor revealed very good selectivities for Al3+ over a wide variety of other metal ions, and could be used at a working pH range of 3.4 - 5.0. It was used as an indicator electrode in potentiometric titration of aluminum ions with EDTA, and in the determination of Al3+ in different real samples.     

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 5.0x10(-6)-1.0x10(-1) M with a Nernstian slope of 59 mV per decade. The detection limit of electrode is 5.0x10(-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.     

An Eu(III) sensor based on N,N-diethyl-N-(4-hydroxy-6-methylpyridin-2-yl)guanidine.

A highly selective poly(vinyl chloride)-based membrane sensor produced by using N,N-diethyl-N-(4-hydroxy-6-methylpyridin-2-yl)guanidine (GD) as active material is described. The electrode displays Nernstian behavior over the concentration range 7.0 x 10(-5) - 1.0 x 10(-1) M. The detection limit of the electrode is 5.0 x 10(-5) M. The best performance was obtained with the membrane containing 30% PVC, 55% benzyl acetate, 5% GD and 10% oleic acid. The response of the sensor is pH-independent in the range of 3.0 - 7.0. The sensor possesses satisfactory reproducibility, fast response time (< 20 s), and specially excellent discriminating ability for Eu(III) ion with respect to the alkali, alkaline earth, transition and heavy metal ions. The membrane sensor was used as an indicator electrode in potentiometric titration of Eu(III) ion with EDTA. It was also applied in determination of fluoride ions in mouth wash preparations.     

Highly selective iodide membrane electrode based on a cerium salen.

A highly selective PVC membrane electrode based on a cerium-salen complex was prepared. The sensor displays an anti-Hofmeister selectivity sequence with a preference for iodide ion over many common organic and inorganic anions. The proposed electrode exhibits a near-Nernstian behavior over a wide concentration range (5.0 x 10(-2) - 8.0 x 10(-6) M) with a slope of 57.5 mV per decade, and a detection limit of 6.0 x 10(-6) M. The electrode has a very fast response time and can be used in the pH range of 3.0 - 1 1.0. It was applied, as an indicator electrode, in potentiometric titration of Ag+ ions.     

Lead(II)-Selective Membrane Electrode Based on Tetraphenylporphyrin

ABSTRACT

A PVC membrane electrode for Pb² ions based on tetraphenylporphyrin was prepared. The sensor exhibits a Nernstian response for lead ions over a wide concentration range (1.0 x 10^?5-1.0 x 10^?2 M). The limit of detection is 8.5 x 10^?6M. It has a response time of 15 s and can be used for at least three months without any divergence in potential. The proposed electrode shows a fairly good discriminating ability towards Pb² ion in comparison to some alkali, alkaline earth, transition and heavy metal ions. The electrode can be used in the pH range 5.0 to 7.5. It was used as an indicator electrode in potentiometric titration of lead ion.     

Clotrimazole-triiodide ion association as an ion exchanger for a triiodide ion-selective electrode.

A novel triiodide ion-selective electrode based on a clotrimazole-triiodide ion pair as a membrane carrier was prepared. It has a linear response to triiodide from 8 x 10(-6) to 5 x 10(-3) M with a slope of -68.9 mV per decade and a detection limit of 5 x 10(-6) M. The electrode response is independent of the pH of the solution in the pH range 2-9. It has a very short response time and can be used for at least 3 months without any considerable divergence in the potentials. The proposed sensor revealed very good selectivities for I3- over a variety of other anions. It was used as an indicator electrode in the potentiometric titration of triiodide ions and in an indirect potentiometric determination of clotrimazole in pharmaceutical preparations.     

Uranyl-selective PVC membrane electrodes based on some recently synthesized benzo-substituted macrocyclic diamides

Four different recently synthesized macrocyclic diamides were studied to characterize their abilities as uranyl ion carriers in PVC membrane electrodes. The electrodes based on macrocycle 1,18-diaza-3,4;15,16-dibenzo-5,8,11,14,21,24-hexaoxacyclohexaeicosane-2,17-dione resulted in a Nernstian response for UO(2)(2+) ion over wide concentration ranges. The linear concentration range for the polymeric membrane electrode (PME) is 3.0x10(-6)-8.2x10(-3) M with a detection limit of 2.2x10(-6) and that for the coated graphite electrode (CGE) is 5.0x10(-7)-1.5x10(-3) M with a detection limit of 3.5x10(-7) M. The electrodes manifest advantages of low resistance, very fast response and, most importantly, good selectivities relative to a wide variety of other cations.     

A PVC plasticized sensor for Ni(II) ion based on a simple ethylenediamine derivative.

A new PVC membrane ion selective electrode which is highly selective towards Ni(II) ions was constructed using a Schiff base containing a binaphthyl moiety as the ionophore. The sensor exhibited a good Nernstian response for nickel ions over the concentration range 1.0x10(-1)-5.0x10(-6) M with a lower limit of detection of 1.3x10(-6) M. It has a fast response time and can be used for a period of 4 months with a good reproducibility. The sensor is suitable for use in aqueous solutions in a wide pH range of 3.6-7.4 and works satisfactorily in the presence of 25% (v/v) methanol or ethanol. The sensor shows high selectivity to nickel ions over a wide variety of cations. It has been successfully used as an indicator electrode in the potentiometric titration of nickel ions against EDTA and also for the direct determination of nickel content in real samples: effluent samples, chocolates and hydrogenated oils.     

Ion-selective electrode for aluminum determination in pharmaceutical substances, tea leaves and water samples

A novel ion-selective PVC membrane sensor for Al(III) ions based on 6-(4-nitrophenyl)-2-phenyl-4-(thiophen-2-yl)-3,5-diaza-bicyclo[3.1.0]hex-2-ene (NTDH) as a new ionophore has been prepared and studied. The electrode exhibit a good response for aluminum ion over concentration range of 1.0x10(-6) to 1.0x10(-1) mol L(-1) with a Nernstian slope of 19.6+/-0.4 mV per decade and low detection limit of 6.3x10(-7) mol L(-1). The best performance was obtained with membrane composition 30% poly(vinyl chloride), 62% acetophenone, 5% oleic acid, 3% ionophore and 2 ml tetrahydrofuran. NTDH-based electrode was suitable for aqueous solutions of pH 3. It has relatively fast response time (approximately 10 s) and can be used at least for 3 months without any considerable divergence in potentials. The proposed membrane electrode revealed good selectivity for Al(III) ions over a wide variety of other cations. The standard electrode potentials were determined at different temperatures and used to calculate the isothermal coefficient of the electrode. The formation constant and stoichiometry ratio of ionophore-Al(III) complex were calculated at 25 degrees C by using segmented sandwich membrane method. It was used in non-aqueous solvents and also as indicator electrode in potentiometric determination of Al(III) ions in some real samples.     

Charge-transfer triiodide ion-selective electrode based on 7,16-dibenzyl-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane.

A new PVC membrane electrode for the triiodide ion based on a charge-transfer complex of iodine with 7,16-dibenzyl-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane as a membrane carrier was prepared. The electrode exhibits a Nernstian response for triiodide ions over a wide concentration range (1.0 x 10(-1)-1.0 x 10(-5) M) with a slope of 59.3 +/- 0.9 mV decade(-1) and a detection limit of 6.3 x 10(-6) M. It has a response time of 30 s and can be used for at least 3 months without any divergence in the potential. The potentiometric response is independent of the pH, in the pH range 1.6 - 10.0. The proposed electrode has shown very high selectivity for the triiodide ion over a wide variety of other anions. This electrode was successfully applied as an indicator electrode in the potentiometric titration of ascorbic acid and hydroquinone from pharmaceutical preparations as well as ascorbic acid in orange juice and dissolved O2 in tap water.     

Highly selective PVC-membrane electrodes based on Co(II)-Salen for determination of nitrite ion.

A cobalt(II) derivative was used as a suitable ionophore for the preparation of a polymeric membrane nitrite-selective electrode. The electrode reveals a Nemstian behavior over a very wide NO2- ion concentration range (1.0 x 10(-6)-1.0 x 10(-1) M) and a very low detection limit (5.0 x 10(-7) M). The potentiometric response is independent of the pH of solution in the pH range 4.0-9.5. The electrode shows advantages such as low resistance, fast response and, most importantly, good selectivity relative to a wide variety of inorganic and organic anions. In fact, the selectivity behavior of the proposed NO2- ion-selective electrode shows great improvements compared to the previously reported electrodes for nitrite ion. The proposed electrodes could be used for at least 2 months without any significant changes in potentials. The electrode was successfully applied to the determination of nitrate ion concentrations in sausage and milk samples.     

Mercury(II) ion-selective electrodes based on p-tert-butyl calix[4]crowns with imine units.

A PVC membrane incorporating p-tert-butyl calix[4]crown with imine units as an ionophore was prepared and used in an ion-selective electrode for the determination of mercury(II) ions. An electrode based on this ionophore showed a good potentiometric response for mercury(II) ions over a wide concentration range of 5.0 x 10(-5) - 1.0 x 10(-1) M with a near-Nernstian slope of 27.3 mV per decade. The detection limit of the electrode was 2.24 x 10(-5) M and the electrode worked well in the pH range of 1.3 - 4.0. The electrode showed a short response time of less than 20 s. The electrode also showed better selectivity for mercury(II) ions over many of the alkali (Na+, -1.69; K+, -1.54), alkaline-earth (Ca2+, -3.30; Ba2+, -3.32), and heavy metal ions (Co2+, -3.67; Ni2+, -3.43; Pb2+, -3.31; Fe3+, -1.82). Ag+ ion was found to be the strongest interfering ion. Also, sharp end points were obtained when the sensor was used as an indicator electrode for the potentiometric titration of mercury(II) ions with iodide and dichromate ions.     

Coated wire silver-ion selective electrode based on a N,N'-bis(2-thienylmethylene)-1,2-diaminobenzene.

A novel membrane coated platinum-wire electrode (MCPWE) based on N,N'-bis(2-thienylmethylene)-1,2-diaminobenzene (BTMD) for highly selective determination of Ag+ ion has been developed. The influences of membrane composition and pH on the potentiometric responses of electrode were investigated. The potentiometric responses are independent of the pH of the test solution in the range of 5.0 - 9.0. The electrode shows a linear response for Ag+ ion over the concentration range of 1.0 x 10(-60 to 1.0 x 10(-1) M with a lower detection limit of 6.0 x 10(-7) M. The electrode possesses a Nernstian slope of 59.7 mV decade(-1) and a fast response time of < or = 17 s and can be used for at least 2 months without any observable deviation. The proposed electrode displayed very good selectivity for Ag+ ion with respect to NH4+ and alkali, alkaline earth and some common transition metal ions. The practical utility of the electrode has been demonstrated by its use as the indicator electrode in the potentiometric titration of an AgNO3 solution with a NaI solution and in determination of the silver content of a developed radiological film.     

Sulfate-selective PVC membrane electrode based on a strontium Schiff's base complex

A strontium Schiff's base complex (SS) can be used as a suitable ionophore to prepare a sulfate-selective PVC-based membrane electrode. The use of oleic acid (OA) and hexadecyltrimethylammonium bromide (HTAB), as additives, and nitrobenzen (NB), dibutyl phthalate (DBP) and benzyl acetate (BA) as solvent mediators, were investigated. The best performance was observed with a membrane composition PVC: NB: SS: HTAB of 30%: 62%: 5%: 3% ratio. The resulting sensor works well over a wide concentration range (1.0 x 10(-2)-1.0 x 10(-6) M) with a Nernstian slope of -29.2 mV per decade of sulfate activity over a pH range 4.0-7.0. The limit of detection of the electrode is 5 x 10(-7) M. The proposed sensor shows excellent discriminating ability toward SO4(2-) ions with regard to many anions. It has a fast response time of about 15 s. The membrane electrode was used to the determination of zinc in zinc sulfate tablets. The sensor was also used as an indicator electrode in the potentiometric titration of SO4(2-) against barium ion.     

Bis(2-hydroxyacetophenone)ethylenediimine as a neutral carrier in a coated-wire membrane electrode for lead(II).

A coated-wire ion-selective electrode (CWISE), based on a Schiff base as a neutral carrier, was successfully developed for the detection of Pb(II) in aqueous solution. CWISE exhibited a linear response with a Nernstian slope of 29.4 +/- 0.5 mV/decade within the concentration range of 1.0 x 10(-5) - 1.0 x 10(-1) M lead ion. CWISE has shown detection limits of 5.0 x 10(-6) M. The electrode exhibited good selectivity over a number of alkali, alkaline earth, transition and heavy metal ions. This sensor yielded a steady potential within 10 to 20 s at a linear dynamic range. The electrode was suitable for use in aqueous solutions in a pH range of 2.0 to 5.0. Applications of this electrode for the determination of lead in real samples and as indicator electrode for potentiometric titration of Pb2+ ion using K2CrO4 are reported.     

Thiocyanate ion-selective PVC membrane electrode based on N,N'-ethylene-bis(4-methylsalicylidineiminato)nickel(II).

A highly selective poly(vinyl chloride) (PVC) membrane electrode based on an N,N'-ethylene-bis(4-methyl-salicylidineiminato) nickel(II) [Ni(EBMSI)] complex as a carrier for a thiocyanate-selective electrode is reported. The influences of the membrane composition, pH and possible interfering anions were investigated based on the response properties of the electrode. The electrode exhibited a good Nernstian slope of -58.9 +/- 0.7 mV decade(-1), over a wide pH range of 3.5 - 8.5 and a linear range of 1.0 x 10(-6) - 1.0 x 10(-1) M for thiocyanate. The detection limit of electrode was 3.1 x 10(-7) M SCN(-). The selectivity coefficients determined by a fixed interference method (FIM) indicate that a good discriminating ability towards the SCN- ion compared to other anions. The proposed sensor had a fast response time of about 5 - 15 s and could be used for at least 3 months without any considerable divergence in the potential. It was applied as an indicator electrode in the titration of thiocyanate with Ag+ and in the potentiometric determination of thiocyanate in saliva and urine samples.     

A mercury(II) ion-selective electrode based on N,N-dimethylformamide-salicylacylhydrazone as a neutral carrier.

A new PVC membrane mercury(II) ion electrode based on N,N-dimethylformamide-salicylacylhydrazone (DMFAS) as an ionophore is described, which shows excellent potentiometric response characteristics and displays a linear log[Hg(2+)] versus EMF response over a wide concentration range between 6.2 x 10(-7) and 8.0 x 10(-2) M with a Nerstian slope of 29.6 mV per decade and a detection limit of 5.0 x 10(-7) M. The response time for the electrode is less than 30 s and the electrode can be used for more than 2 months with less than a 2 mV observed divergence in a potentials. The proposed electrode exhibits very good selectivity for mercury(II) ions over many cations in a wide pH range (pH 1 - 4). The electrode was also applied to the determination of a mercury(II) ion in vegetables and in Azolla filiculoides.     

Lead(II)-selective electrode based on phenyl disulfide.

A PVC membrane electrode for lead ions based on phenyl disulfide as the membrane carrier was developed. The electrode exhibits a good Nernstian slope of 29.3 +/- 0.7 mV/decade and a linear range of 2.0 x 10(-6)-1.0 x 10(-2) M for Pb(NO3)2. The limit of detection is 1.2 x 10(-6) M. It has a response time of 45 s and can be used for at least fifty days without any divergence in potential. The proposed membrane sensor revealed high selectivity for Pb2+ over a wide variety of other metal ions and could be used in the pH range of 3.5-6.3. The electrode was used as an indicator electrode in potentiometric titration of lead ions.     

Preparation of a novel iodide-selective electrode based on iodide-miconazole ion-pair and its application to pharmaceutical analysis.

An iodide-miconazole ion-paired complex was used as a suitable ion-exchanger for the preparation of a plasticized-PVC membrane electrode. Among different solvent mediators tested, dioctylsebacate exhibited the proper response characteristics, including Nernstian slope of the calibration curve, fast response time and good reproducibility of the emf values. The electrode exhibits a Nernstian slope of -59.8 +/- 0.5 mV decade(-1) for I- ion over a concentration range of 1.0 x 10(-5) - 1.0 x 10(-2) M with a limit of detection of 7.0 x 10(-6) M. The electrode displays a good selectivity for I- with respect to a number of inorganic and organic species. It canbe used over a pH range of 2.5 - 8.5. The membrane sensor was successfully applied to the determination of iodide in water samples and blood serum, as well as in pharmaceutical products such as iodoquinol and thyroxin.     

Papaverine PVC membrane ion-selective electrodes based on its ion-exchangers with tetraphenylborate and tetrathiocyanate anions

The construction and general performance of novel potentiometric membrane ion selective electrodes for determination of papaverine hydrochloride has been described. They are based on the formation of the ion association complexes of papaverine (PA) with tetraphenylborate (TPB)(I) or tetrathiocyanate (TTC)(II) counter anions as electro-active material dispersed in a PVC matrix. The electrodes show fast, stable, near Nernstian response for 1 x 10(-2) to 6 x 10(-5) M and 1 x 10(-2) to 1 x 10(-5) M for PA-TPB and PA-TTC respectively at 25 degrees C over the pH range of 3-5.0 with a cationic slope of approximately 56.5 +/- 0.5 mV/decade for both sensors respectively. The lower detection limit is 4 x 10(-5) and 8 x 10(-6) M for PA- I and PA-II respectively with fast response time ranging from 20-45 sec. Selectivity coefficients for PA relative to a number of interfering substances were investigated. There is a negligible interference from the studied cations, anions, and pharmaceutical excipients. The determination of 4.0- 3000.0 microg/ml of PA in aqueous solutions shows an average recovery of 99.1% and a mean relative standard deviation of 1.4 at 100microg/ml. The direct determination of PA in some formulations (Vasorin injection) gave results that compare favorably with those obtained using the British Pharmacopoeia method. Potentiometric titration of PA with sodium tetraphenylborate and potassium thiocyanate as titrants utilizing the papaverine electrode as an end point indicator electrode has been carried out.