Studies on the potentiometric thallium(III)-selective carbon paste electrode and its possible applications

Construction, performance characteristics and applications of a carbon paste thallium(III) ion-selective electrode are described. The electrode, which is based on ion-associate compounds formed between cetylpyridinium and chlorothallate(III) complexes dissolved in tricresyl phosphate as pasting liquid, showed near-Nernstian response over the concentration range of 5.8 × 10^–6– 2.9 × 10^–3 mol/L. Potentiometric titrations of thallium(III) with cetylpyridinium chloride were affected by higher concentrations of excess halides, probably due to the formation of higher halogenothallates.     

Spectrophotometric determination of trace amounts of thallium with 7-(4,5-dimethylthiazolyl-2-azo)-8-hydroxyquinoline-5-sulphonic acid

A new reagent, 7-(4,5-dimethylthiazolyl-2-azo)-8-hydroxyquinoline-5-sulphonic acid, has been examined to evaluate its usefulness as a spectrophotometric reagent for thallium(III). A purple-red complex is formed in aqueous solution at pH 4-5 in the presence of cetylpyridinium chloride and the stoichimetric ratio is 1:2 (Tl:reagent). The apparent stability constant is 1.5 x 10(11). The effect of diverse ions has been studied and a method for determining trace amounts of thallium is proposed.     

A simple and rapid spectrophotometric determination of thallium(III) with trifluoperazine hydrochloride.

A simple, sensitive and rapid spectrophotometric method was developed for the determination of thallium(III) using trifluoperazine hydrochloride (TFPH). The method is based on the oxidation of TFPH by thallium(III) in a phosphoric acid medium to form a red-colored radical cation with an absorption maximum at 505 nm. Beer's law is valid over the concentration range of 0.5 - 6.5 microg ml(-1) of thallium(III). The molar absorptivity and Sandell's sensitivity of the color system are 2.14 x 10(4) l mol(-1) cm(-1) and 0.0095 microg cm(-2), respectively. The optimum reaction conditions and other analytical parameters were evaluated. The tolerance limit of the method towards various ions usually associated with thallium has been studied. The proposed method has been successfully applied to the analysis of thallium in alloys, minerals, standard reference material, water, and urine 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.     

A PVC-coated carbon rod ion-selective electrode for thallium and its application to the analysis of rocks and minerals

A new Tl(III) ion-selective electrode prepared by coating a graphite rod with a PVC membrane has been made and investigated. The optimum membrane composition is Butylrhodamine B-TlCl(-)(4) 5 mg, chlorobenzene 0.1 ml, dioctyl phthalate 0.4 ml, PVC 0.17 g. The electrode exhibits Nernstian response to Tl(III) over the concentration range 6.5 x 10(-7)-2.5 x 10(-3)M. The detection limit is 3.5 x 10(-7)M and the slope of the electrode response is 53 +/- 1 mV per decade. The electrode shows high stability and selectivity. The electrode is easy to make and store, and inexpensive.     

Direct potentiometric determination of tin(II) and (IV), antimony(III), thallium(III), rhenium(VII), and bismuth(III) with cetylpyridinium chloride

Summary The precipitation titrations of the following elements vs. cetylpyridinium chloride were investigated: Rhenium as perrhenate, tin as the (II) and (IV) species, antimony(III), thallium(III), and bismuth(III) as their halogen complexes. Optimum conditions for the determinations are described. Of the elements examined only thallium(III) also could be titrated potentiometrically vs. tetraphenylarsonium chloride. Titrations were monitored with a simple sensor consisting of a graphite rod coated with poly(vinyl chloride) and dioctylphthalate, and a double-junction reference electrode.

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Direkte potentiometrische Bestimmung von Zinn(II) und (IV), Antimon(III), Thallium(III), Rhenium(VII) und Bismut(III) mit Hilfe von Cetylpyridiniumchlorid

Zusammenfassung Die Fällungstitration der genannten Elemente mit Cetylpyridiniumchlorid wurde untersucht: Re als Perrhenat; Zinn in 3- und 4wertiger Form; Sb(III), Tl(III) und Bi(III) in Form ihrer Halogenkomplexe. Die optimalen Bedingungen werden mitgeteilt. Nur Thallium(III) kann auch potentiometrisch gegen Tetraphenylarsoniumchlorid titriert werden. Die Titrationen werden mit Hilfe eines einfachen Sensors kontrolliert, der aus einem mit Polyvinylchlorid und Dioctylphthalat überzogenen Graphitstab besteht sowie einer double-junction Bezugselektrode.

     

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.     

PVC membrane ion selective electrode for the determination of pentachlorophenol in water, wood and soil using tetrazolium pentachlorophenolate

A novel PVC membrane electrode selective for the determination of pentachlorophenolate (PCP) ion based on 2,3,5-triphenyl-2H-tetrazolium (TPT) pentachlorophenolate ion pair as an electroactive material is described. The electrode shows a linear response for PCP ion over the concentration range of 6x10(-5) to 1x10(-2) M with lower detection limit of 4x10(-5) M at 25 degrees C. The electrode posses a Nernstian slope of -55.0+/-1.0 mV/decade and a fast potential response of 45 s, which is almost constant over a pH range of 5.5-10.5. Selectivity coefficient data for some common ions show negligible interference, however, 2,4,6-trichlorophenolate and cetylpyridinium ions interfere. An average recovery of 96.2% with relative standard deviation of 2.3% has been achieved for the determination of 75.0 ppm PCP in wastewater samples. The determination of PCP in soil and wood samples gave results that compare favorably with those obtained by gas chromatography. The electrode has been utilized as an end point indicator electrode for the determination of PCP using potentiometric titration.     

Solid Membranes of Copper Hriacyanoferrats (III) as Thallium (I) Sensitive Electrode

Abstract

Solid membranes of copper hexacyanoferrate (III) in Areldite are evaluated as thallium (I) sensitive electrode. The membrane electrode gave a linear near Normstian response to thallium (I) ions in the concentration range 10^?1 - 5 × 10^?4 M and can be used to estimate T1 (I) down to 10^?4 M. The responses of the electrode is fast and steady potentials are obtained in less than a minute. The same membrane has been used over a period of six months without any appreciable drift in potential. The electrode can also be used satisfactory in partially non-aqueous media and in presence of a number of interfering ions. It is superior to the existing T1(I) solid membrane electrodes as it can function in alkaline range also.     

New plastic membrane and carbon paste ion selective electrodes for the determination of triprolidine.

Triprolidine (Trip) ion selective electrodes of three types: the conventional polymer membrane (I), graphite coated electrode (II) and carbon paste electrode (III), have been prepared, based on the ion pair of triprolidine hydrochloride with sodium tetraphenylborate. The electrodes exhibit a linear response with a mean calibration graph slope of 56.12, 55.00 and 54.32 mV decade(-1) at 25 degrees C for I, II and III, respectively, within the concentration ranges 1.96 x 10(-5) - 1.00 x 10(-2) M for I and 3.84 x 10(-5) - 1.00 x 10(-2) M for II and III. The detection limits are 1.13+/-0.13 x 10(-5), 1.70+/-0.06 x 10(-5) and 1.78+/-0.05 x 10(-5) M for the three electrodes, respectively. The change of pH within the ranges 4.85 - 8.75 and 4.70 - 8.50 for I and III, respectively, did not affect the electrode performance. The standard electrode potentials were determined at different temperatures and were used to calculate the isothermal coefficient of the electrode. The electrodes showed a very good selectivity for Trip with respect to a large number of inorganic cations and compounds. The standard addition method was applied to the determination of TripCl in pure solution, pharmaceutical preparations, and urine samples.     

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.     

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.     

Coated-wire ion-selective electrode for the determination of gold(III)

A coated-wire gold(III)-selective electrode based on the 1,2,4,6-tetraphenyl-pyridinium tetrachloroaurate(III) ion-pair is described. The response is Nernstian in the gold concentration range 10^?2–3 × 10^?6 (slope 59.0 mV/pAu). Of the 22 ions tested, only the interference of thallium(III) is important. The electrode is applied to the determination of gold in an Ag-Pd-Au alloy with satisfactory results.     

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.     

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.     

Flow injection fluorimetric determination of thiourea

A flow injection configuration for the fluorimetric determination of thiourea is proposed. The procedure is based on the rapid oxidation of thiourea by thallium(III) with concomitant formation of fluorescent thallium(I). Linear calibration graphs were obtained between 5 x 10(-7) and 1 x 10(-5)M, with a sampling rate of 90 samples/hr. The usefulness of the method was tested in the determination of thiourea in fruit juices and fruit peels.     

Cetylpyridinium-iodomercurate PVC membrane ion selective electrode for the determination of cetylpyridinium cation in Ezafluor mouth wash and as a detector for some potentiometric titrations

A potentiometric method is described for the determination of cetylpyridinium (CP) cation using a polyvinyl chloride powder (PVC) membrane sensor based on CP-iodomercurate ion pair as an electroactive material. The sensor shows a linear response for CP ion over the concentration range of 2x10(-6)-1x10(-3) M at 25 degrees C. The electrode posses a sub-Nernstian slope of 29.0+/-0.4 mV decade(-1), which has been thoroughly discussed.The electrode shows a fast potential response of approximately 50 s, which is almost constant over a pH range of 3.0-6.0. Selectivity coefficient data for some common ions show negligible interference, however, cetyltrimethylammonium bromide (CTMAB) interferes significantly. An average recovery of 98.8% for CP with an average relative standard deviation (R.S.D.) of 1.2% has been achieved. The determination of CPC in Ezafluor mouth wash gave result that compare favorably with those obtained by the British Pharmacopoeia method. The CP electrode has been utilized as an end point indicator electrode in potentiometric titration of some anions, and applied for the determination of anionic surfactants in some commercial detergents and waste water.     

Determination of gold using clay modified carbon paste electrode

Sorption of gold(III) chlorocomplexes was studied by means of a carbon paste electrode modified with montmorillonite. Anionic exchange behavior was found in chloride media with low ionic strength. Anionic sorption of [AuCl4]- can be used as a preconcentration step to the determination of Au(III). Linear calibration dependences were found in the concentration range 4.06 x 10(-6) - 1.22 x 10(-5) mol/L Au(III) after 5 min of sorption and in the range 8.12 x 10(-7) - 6. 1 x 10(-6) mol/L after 10 min of sorption. Interferences of several anions and cations were studied. Model samples of table water were analyzed.     

Development and analytical applications of a new liquid-membrane 3,5-dinitrosalicylate-selective electrode

A 3,5-dinitrosalicylate (DNS)-selective electrode with a liquid membrane of either tetraphenyIphosphonium-DNSH dissolved in p-nitrocumene or dimethyldioctadecylammonium-DNSH dissolved in 1-decanol is described. The liquid membrane electrode exhibits rapid and near-Nemstian response to DNSH- activity from 10^-2 to 10^-5 M. The response is unaffected by pH in the range 2.5–6.5. The electrode has been successfully applied in the direct potentiometric titration of iron(III) and copper(II) with EDTA and in the indirect titrimetric determination of aluminium(III) and nickel(II). It is also useful in titrations of bulky quaternary cations such as cetyltrimethylammonium, cetylpyridinium and didodecyldimethylamnionium ions with DNSHNa.     

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.