A selective membrane electrode for lanthanum(III) ion based on a hexaaza macrocycle derivative as ionophore.

We have developed a highly La(III)-selective PVC membrane electrode based on a hexaaza macrocycle, 8,16-dimethyl-6,14-diphenyl-2,3,4:10,11,12-dipyridine-1,3,5,9,11,13-hexaazacyclohexadeca-3,5,8,11,13,16-hexaene [Bzo2Me2Pyo2(16)-hexaeneN6] (I) as membrane carrier, dibutylbutyl phosphonate (DBBP) as solvent mediator and sodium tetraphenylborate (NaTPB) as lipophilic additive. The best performance was given by the membrane of macrocycle I having a composition 10:260:5:120 (I:DBBP:NaTPB:PVC). The electrode exhibits a Nernstian response to La(III) ion in the concentration range 1.0x10(-1)-7.94x10(-7) M with a slope of 19.8+/-0.2 mV/decade of concentration and a detection limit of 5.62x10(-7) M. The response time of the sensor is 12 s and it can be used over a period of 4 months with good reproducibility. The electrode works well over a pH range of 2.5-10.0 and in partially non-aqueous medium with up to 30% organic content. The sensor was also used as an indicator electrode in potentiometric titration of La(III) ions with EDTA and for determining La(III) concentration in real samples.     

Spectrophotometric determination of vitamin E (alpha-tocopherol) using copper(II)-neocuproine reagent

A coated graphite-epoxy ion-selective electrode for bismuth(III), based on the ion-pair between the [Bi(EDTA)](-) anion and tricaprylylmethylammonium cation (Aliquat 336S) incorporated onto a poly(vinylchloride) (PVC) matrix is constructed. A thin membrane film of this ion-pair, dibutylphthalate (DBPh) or ortho-nitrophenyloctylether (o-NPOE) in PVC was deposited directly onto a Perspex(R) tube which contained a graphite-epoxy conductor substrate attached to the end of a glass tube. The coating solution was prepared by dissolving 30% (w/w) of PVC in 10 ml of tetrahydrofuran following addition of 65% (w/w) DBPh or o-NPOE and 5% (w/w) of the ionic pair. The effect of pH, EDTA concentration and some cation and anion on the electrode response is investigated. The bismuth(III) ion-selective electrode shows a linear response in the bismuth(III) concentration range from 1.0 x 10(-8) to 1.0 x 10(-1) mol 1(-1) and 1.0 x 10(-7) to 1.0 x 10(-1) mol 1(-1) and a slope of 56.8 and 59.2 mV dec.(-1) for the polymeric membranes containing DBPh and o-NPOE, respectively. The lifetime of this electrode was superior to 1 year (over 1600 determinations for each polymeric membrane), with practical detection limits of 6.3 x 10(-9) and 4.4 x 10(-8) mol 1(-1) with these plasticizers. Application of this electrode with bismuth(III) determination in a stomach anti-acid sample is described.     

Synthesis of N'-(1-pyridin-2-ylmethylene)-2-furohydrazide and its application in construction of a highly selective PVC-based membrane sensor for La(III) ions.

A highly La(III) ion-selective PVC membrane sensor based on N'-(1-pyridin-2-ylmethylene)-2-furohydrazide (NPYFH) as an excellent sensing material was successfully developed. The electrode shows a good selectivity for La(III) ion with respect to most common cations including alkali, alkaline earth, transition and heavy metal ions. The proposed sensor exhibits a wide linear response with slope of 19.2 +/- 0.6 mV per decade over the concentration range of 1.0 x 10(-6) - 1.0 x 10(-1) M, and a detection limit of 7.0 x 10(-7) M of La(III) ions. The sensor response is independent of pH in the range of 3.5-10.0. The proposed electrode was applied as an indicator electrode in potentiometric titration of La(III) ion with EDTA.     

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.     

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.     

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.     

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.     

A novel tetrachlorothallate (III)-PVC membrane sensor for the potentiometric determination of thallium (III)

A novel tetrachlorothallate (III) (TCT)-selective membrane sensor consisting of tetrachlorothallate (III)-2,3,5-triphenyl-2-H-tetrazolium ion pair dispersed in a PVC matrix plasticized with dioctylphthalate is described. The electrode shows a stable, near-Nernstian response for 1×10⁻³-4×10⁻⁶ M thallium (III) at 25 °C with an anionic slope of 56.5±0.5 over the pH range 3-6. The lower detection limit and the response time are 2×10⁻⁶ M and 30-60 s, respectively. Selectivity coefficients for Tl(III) relative to a number of interfering substances were investigated. There is negligible interference from many cations and anions; however, iodide and bromide are significantly interfere. The determination of 0.5-200 μg ml⁻¹ of Tl(III) in aqueous solutions shows an average recovery of 99.0% and a mean relative standard deviation of 1.4% at 50.0 μg ml⁻¹. The direct determination of Tl(III) in spiked wastewater gave results that compare favorably with those obtained by the atomic absorption spectrometric method. The electrode was successfully applied for the determination of thallium in zinc concentrate. Also the tetrachlorothallate electrode has been utilized as an end point indicator electrode for the determination of thallium using potentiometric titration.     

Synthesis of a new oxime and its application to the construction of a highly selective and sensitive Co(II) PVC-based membrane sensor.

A cobalt(II) ion-selective membrane sensor has been fabricated from a poly vinyl chloride (PVC) matrix membrane containing a new oxime compound (oxime of 1-(2-oxocyclohexyl)-1,2-cyclohexanediol, OXCCD) as a neutral carrier, sodium tetraphenyl borate (NaTPB) as an anionic excluder and o-nitrophenyloctylether (o-NPOE) as a plasticizing solvent mediator. The membrane sensor exhibits a linear potential response in the concentration range of 1.0 x 10(-1) - 1.0 x 10(-6) M of Co2+. The electrode displays a Nernstian slope of 29.8 mV decade(-1) in the pH range of 3.5 - 8.0. The sensor also exhibits a fast response time of < 25 s. The detection limit of the proposed sensor is 9.0 x 10(-7) M (approximately 40 ng/ml), and it can be used over a period of two months. The selectivity of the sensor with respect to other cations (alkali, alkaline earth, transition and heavy metal ions) is excellent. The practical utility of the sensor has been demonstrated by using it as an indicator electrode in the potentiometric titration of Co2+ with EDTA and for the direct determination of Co(II) in wastewater of the electroplating industry.     

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.     

Novel sulfate ion-selective polymeric membrane electrode based on a derivative of pyrilium perchlorate

A sulfate ion-selective PVC membrane sensor based on 4-(4-bromophenyl)-2,6-diphenylpyrilium perchlorate (BDPP) as a novel sensing material is successfully developed. The electrode shows a good selectivity for sulfate ion with respect to common organic and inorganic anions. The sensor exhibits a good linear response with slope of -28.9+/-0.5 mV per decade over the concentration range of 1.0x10(-6)-1.0x10(-2) M, and a detection limit of 8.0x10(-7) M of SO(4)(2-) ions. The electrode response is independent of pH in the range of 4.0-9.0. The proposed sensor was applied as an indicator electrode in potentiometric titration of sulfate and barium ions, and to the determination of zinc in zinc sulfate tablets.     

Co2+-selective membrane electrode based on the Schiff Base NADS

A new PVC membrane electrode for cobalt(II) ions based on a recently synthesized Schiff base of 5-((4-nitrophenyl)azo)- N-(2',4'-dimethoxyphenyl)salicylaldimine is reported. The electrode exhibits a Nernstian response for Co(2+) ions over a wide concentration range (9.0 x 10(-7)-1.0 x 10(-2) M) with a slope of 29(+/-1). The limit of detection is 8.0 x 10(-7) M. The proposed sensor revealed good selectivities over a wide variety of other cations including hard and soft metals. This electrode could be used in a pH range of 3.5-6.0. It was used as an indicator electrode in potentiometric titrations of cobalt(II) ions and can be used in the direct determination of Co(2+) in aqueous solutions.     

Chromium(III) ion-selective electrode based on 4-dimethylaminoazobenzene

A PVC-based membrane of 4-dimethylaminoazobenzene reveals a Nernstian potentiometric response (with slope of 19.5+/-0.6 mV/decade and a correlation coefficient of 0.999) for Cr(III) over a wide concentration range (1.66 x 10(-6)-1.0 x10(-2) mol dm(-3)). The potential of this electrode is independent of pH in the range of 3.0-5.5. It has a fast response time of about 10 s and was used for a period of 3 months with good reproducibility. The detection limits of this membrane electrode was 8 x 10(-7) M. the proposed electrode has been used as an indicator electrode in the potentiometric titration of Cr(III) with EDTA. This sensor exhibits a very good selectivities for Cr(III) over a wide variety of metal ions.     

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.     

Ion-selective electrodes in organic analysis-determination of xanthate

A PVC membrane xanthate-selective electrode has been developed for the direct determination of xanthates of primary and secondary alcohols. The xanthate electrode is highly selective and exhibits a Nernstian response in the range 5.0 x 10(-2)-7.1 x 10(-5)M xanthate with a slope of 58.6 mV per concentration decade. The electrode has a wide working pH range (5.0-11.5), a fast response time (less than 30 sec) and is stable for at least two months.     

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 sensitive and specific method for isoniazid determination based on selective adsorption using an isoniazid ion-selective piezoelectric sensor

A selective, sensitive and simple ion-selective piezoelectric (ISP) sensor was developed for the direct determination of isoniazid (INH) in body fluids. Based on sensitive mass response of piezoelectric quartz crystal and selective adsorption/desorption across the modified film, the ISP sensor was fabricated by coating a PVC film containing activant on one electrode of a thickness-shear mode piezoelectric quartz crystal. The observed frequencies of ISP sensor were found to decrease with the increase of the INH concentration in a 0.1 M NaNO(3) solution. In this paper, three activants, INH-phosphotungstate (I), INH-silicotungstate (II), and INH-[BiI(4)](-) (III), were synthesized and investigated. Calibration graphs were linear from 6x10(-8) to 2x10(-3) M for I, 2x10(-7) to 2x10(-3) M for II and 2x10(-7) to 2x10(-3) M for III, with detection limits 6x10(-8) M for I, 2x10(-7) M for II and 2x10(-7) M for III, in a 0.1 M NaNO(3) solution at pH 7.0 and 37 degrees C. Recoveries were from 98% to 102% with R.S.D. up to 2%. Results for real samples obtained by the proposed method agreed well with those obtained by the conventional pharmacopeia method.     

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.     

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.     

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.