Construction of different types of ion-selective electrodes and validation of direct potentiometric determination of phenytoin sodium

The construction and performance characteristics of phenytoin sodium selective electrodes are detailed. Two types of electrodes: plastic membrane I and coated wire II, were constructed based on the incorporation of phenytoin sodium with tungstosilicic acid. The influence of membrane composition, kind of plasticizer, pH of the test solution, soaking time and the electrodes’ foreign ions were investigated. The electrodes showed a Nernstian response with a mean calibration graph slope of 30.9±0.1 and 28.9±0.1 mV decade⁻¹ at 25°C for electrode I and II respectively, over a phenytoin sodium concentration range of 5×10⁻³−5×10⁻⁶ M and 1×10⁻³−1×10⁻⁶ M with a detection limit 1.3×10⁻⁶ M and 2.5×10⁻⁷ M for electrode I and II, respectively. The electrodes gave average selective precision and were usable within the pH range 6–10. Interference studies from common cations, alkaloids, sugars, amino acids and drug excipients are reported. The results obtained by the proposed electrodes were also applied successfully for the determination of the drug in pharmaceutical preparations and biological fluids.     

Poly(aniline) solid contact ion selective electrode for udenafil

Udenafil is an oral agent for treating male erectile dysfunction. The poly(aniline) solid contact selective electrodes for udenafil have been fabricated from PVC cocktail solutions with three ion selective ion pairs. This solid contact electrode contains three layers of Pt/electro-conductive poly(aniline) polymer/PVC film with an ionophore with a thickness of 2.5 ± 0.1 mm. We compared the slopes of EMF responses and the response range of a solid contact electrode based on Udenafil-TmCIPB ion pair with those based on Udenafil-PMA and Udenafil-TPB ion pairs and showed that the response slopes were influenced by plasticizers. The EMF response slopes of Udenafil-TmCIPB-based solid contact electrodes equalled 58.0 mV/decade (at 20 ± 0.2°C) and their linear response dynamic ranges were 1.0 × 10⁻²∼1.0 × 10^−5.85 M (r ² = 0.9984). When electrodes with 6 different plasticizers based on Udenafil-TmCIPB were compared, as the dielectric constant of PVC plasticizer increased, so was the response slope at the same time. Having applied the electrodes to artificial serum directly, we could get same satisfactory results [Nernstian slope: 60.3 mV/decade, dynamic range: 1.0 × 10⁻²∼1.0 × 10^−5.78 M (r ² = 0.9978) in artificial serum]. Solid contact electrodes with Udenafil-TmCIPB have shown the best selectivity, reproducibility of EMF, long-term stability, and short response time (< 20 s).     

Silver(I)-selective membrane potentiometric sensor based on two recently synthesized ionophores containing calix[4]arene

Two new PVC membrane electrodes that are highly selective to Ag(I) ions were prepared using (L₁) calyx[4]arene (L₂) as two suitable neutral carriers. The silver(I) ion selective electrodes exhibit a good response for silver ion over a wide concentration range of 1.0 × 10⁻¹ to 4.2 × 10⁻⁶ M (L₁) and 1.0 × 10⁻¹ to 6.5 × 10⁻⁶ M (L₂) with a Nernstian slope of 60 mV per decade (L₁) and 58 mV per decade (L₂) at 25°C, and was found to be very selective, precise, and usable within the pH range 4.0–8.0. They have a response time of <15 s and can be used for at least 3 months without any measurable divergence in potential. The proposed sensors show a fairly good discriminating ability towards Ag⁺ ion in comparison to some hard and soft metal ions. The electrodes were used as indicator electrodes in the potentiometric titration of silver ion and in the determination of Ag⁺ in photographic emulsion and radiographic and photographic films. Published in Russian in Elektrokhimiya, 2009, Vol. 45, No. 7, pp. 862–868. The article is published in the original.     

Determination of thiocyanate ions at nanolevel in real samples using coated graphite electrode based on synthesised macrocyclic Zn(II) complex

The electrode characteristics and selectivities of PVC-based thiocyanate selective polymeric membrane electrode (PME) incorporating the newly synthesized zinc complex of 6,7:14,15-Bzo₂-10,11-(4-methylbenzene)-[15]-6,8,12,14-tetraene-9,12-N₂-1,5-O₂ (I ₁ ) and zinc complex of 6,7:14,15-Bzo₂-10,11-(4-methylbenzene)-[15]-6,14-diene-9,12-dimethylacrylate-9,12-N₂-1,5-O₂ (I ₂ ) are reported here. The best response was observed with the membrane having a composition of I₂:PVC:o-NPOE:HTAB in the ratio of 6:33:59:2 (w/w; milligram). This electrode exhibited Nernstian slope for thiocyanate ions over working concentration range of 4.4 × 10⁻⁷ to 1.0 × 10⁻² mol L⁻¹ with detection limit of 2.2 × 10⁻⁷ mol L⁻¹. The performance of this electrode was compared with coated graphite electrode (CGE), which showed better response characteristics w.r.t Nernstian slope 59.0 ± 0.2 mV decade⁻¹ activity, wide concentration range of 8.9 × 10⁻⁸ to 1.0 × 10⁻² mol L⁻¹ and detection limit of 6.7 × 10⁻⁸ mol L⁻¹. The response time for CGE and PME was found to be 8 and 10 s, respectively. The proposed electrode (CGE) was successfully applied to direct determination of thiocyanate in biological and environmental samples and also as indicator electrode in potentiometric titration of SCN⁻ ion.     

Solid-state Cu (II) ion-selective electrode based on polyaniline-conducting polymer film doped with copper carmoisine dye complex

A pencil graphite electrode coated by copper (II)–carmoisine dye complex in polyaniline (emeraldine base form) matrix (termed as PGE/PA/Cu-Car) was prepared and used as copper ion-selective electrode. The introduced electrode was found to have high selectivity toward copper ion (II) and exhibited wide working concentration range, low response time, and good shelf life. The sensor electrode showed a linear Nernstian response over the range of 5.0 × 10⁻⁶ to 1.0 × 10⁻¹ M with a slope of 29.7 ± 1 mV per decade change in concentration. A detection limit of 2.0 × 10⁻⁶ M was obtained. The optimum pH working range of the electrode was found to be 4.0–7.0.     

PVC-based Cu (II)-Schiff base complex membrane coated graphite electrode for the determination of the triiodide ion

A triiodide-selective electrode based on copper (II)-Schiff base complex as a membrane carrier is proposed. The electrode was prepared by incorporating the carrier into a plasticized polyvinylchloride (PVC) membrane and was directly coated on the surface of a graphite electrode. The obtained electrode showed a near Nernstian slope of 57.0 ± 0.4 mV/decade to I ₃ ⁻ ions over an activity range of 1.0 × 10⁻⁵−1.0 × 10⁻¹ M with a limit of detection of 4.8 × 10⁻⁶ M. The response time of the electrode was fast (5 s) and the electrode could be used for about 2 months without considerable divergence in response. The potentiometric selectivity coefficients were evaluated and displayed anti-Hofmeister behavior. The electrode was used as an indicator electrode in the potentiometric titration of the triiodide ion and in the determination of ascorbic acid in vitamin C tablets. The text was submitted by the authors in English.     

Application of a trazodone-selective electrode to pharmaceutical quality control and urine analyses

A trazodone-selective electrode for application in pharmaceutical quality control and urine analysis was developed. The electrode is based on incorporation of a trazodone-tetraphenylborate ion exchanger in a poly(vinyl chloride) membrane. The electrode showed a fast, stable and Nernstian response over a wide trazodone concentration range (5 × 10⁻⁵−1 × 10⁻² M) with a mean slope of 59.3 ± 0.9 mV/dec of concentration, a mean detection limit of 1.8 × 10⁻⁵± 2.2 × 10⁻⁶ M, a wide working pH range (5–7.5) and a fast response time (less than 20 s). The electrode also showed good accuracy, repeatability, reproducibility and selectivity with respect to some inorganic and organic compounds, including the main trazodone metabolite. The electrode provided good analytical results in the determination of trazodone in pharmaceuticals and spiked urine samples; no extraction steps were necessary. Dissolution testing of trazodone tablets, in different conditions of pH and particle size, based on a direct potentiometric determination with the new selective electrode is presented as well.     

Iodide ion selective poly(aniline) solid contact electrode based on quinine-cu ionophores

Iodide ion selective poly(aniline) solid contact electrode based on quinine-Cu ionophore as a sensing material has been successfully developed. The electrode exhibits good linear response of 52.0 mV/decade (at 20 ± 0.2°C, r ² = 0.9998) within the concentration range of 1 × 10^−6.4–1 × 10^−1.0 M KI. The composition of this electrode was quinine-Cu 2.0: PVC 30.0: bis(2-ethylhexyl)sebacate 68.0 (mass). This plasticizer provides the best response characteristics. The electrode shows good selectivity for iodide ion in comparison with any other anions and is suitable for use with aqueous solutions of pH 3.3–9.4. The standard deviations of the measured EMF difference were ±1.4 and ±1.3 mV for iodide sample solutions of 1.0 × 10⁻² M and 1.0 × 10⁻³ M, respectively. The stabilization time was less than 10 min and response time was less than 15 sec.     

Construction and Analytical Applications of Plastic Membrane Electrodes for Oxytetracycline Hydrochloride

 Oxytetracycline hydrochloride-selective electrodes of both the coated wire and the conventional polymer membrane types based on oxytetracyclinium phosphotungstate and phosphomolybdate have been prepared. A Nernstian response is shown by these electrodes within 1.0×10⁻⁶–1.0×10⁻² M concentration ranges depending on the type of electrode. The response is unaffected by the change of pH over the range 4–11. The standard electrode potentials, E°, were determined at different temperatures and used to calculate the isothermal temperature coefficients of the electrodes. The electrodes show good selectivity to oxytetracycline hydrochloride with respect to many inorganic cations, sugars and amino-acids. Oxytetracycline hydrochloride is determined successfully in pure solutions and in pharmaceutical preparations using calibration by standard addition and potentiometric titration. A regeneration process for the exhausted electrodes has been developed. Received February 2, 2000. Revision April 7, 2000.     

Highly-sensitive ion selective electrode based on molecularly imprinted polymer particles for determination of tetracycline in aqueous samples

In this work, a highly-sensitive polymeric membrane ion selective electrode for determination of tetracycline was constructed by using molecularly imprinted polymer (MIP) particles as quasi-ionophore. The water-compatible MIP particles targeting tetracycline were synthesized with tetracycline as a template molecule, methacrylic acid as a functional monomer, ethylene glycol dimethacrylate as a cross-linker, 2,2′-azobisisobutyronitrile as an initiator and lanthanum ion as a mediator. Benefited from the distinctive performance of the quasi-ionophore and the optimized composition of the membrane and the inner filling solution, the lower detection limit of the electrode was decreased to about 1 × 10⁻⁸ mol/l. It exhibited a good electrode slope 59.8 mV/decade near the theoretical Nernstian one, with a wide linear working range from 2.0 × 10⁻⁸ to 1.0 × 10⁻³ mol/l. Due to the specific recognition of tetracycline by the MIP particles, the selectivity coefficients for routine interferences were less than 10⁻⁴. The fabricated electrode should be used in pH 2–4, response time of which was less than 200 s when the concentration of tetracycline was higher than 1.0 × 10⁻⁶ mol/l and no more than 30 min at the concentration of 1.0 × 10⁻⁸ mol/l. Finally, the proposed highly-sensitive ion selective electrode has been successfully applied to the determination of tetracycline in aqueous samples.     

Fabrication of an iron(III)-selective PVC membrane sensor based on a bis-bidentate Schiff base ionophore

A Fe³⁺ ion-selective membrane sensor was fabricated from polyvinyl chloride (PVC) matrix membrane containing bis-bidentate Schiff base (BBS) as a neutral carrier, sodium tetraphenyl borate (NaTPB) as anionic excluder, and o-nitrophenyloctyl ether (NPOE) as a plasticizing solvent mediator. The effects of the membrane composition, pH, and additive anionic influence on the response properties were investigated. The best performance was obtained with a membrane containing 32% PVC, 62.5% NPOE, 3% BBS, and 2.5% NaTPB. The electrode shows a Nernstian behavior (slope of 19.3 ± 0.6) over a very wide iron ion concentration range (1.0 × 10⁻⁷–1.0 × 10⁻² M) and has a low detection limit (7.4 × 10⁻⁸ M). The potentiometric response of the sensor is independent of pH of the solution in the pH range 1.9–5.1. The proposed sensor has a very low response time (<15 s) and a good selectivity relative to a wide variety of other metal ions including common alkali, alkaline earth, heavy, and transition metal ions. The electrode can be used for at least 60 days without any considerable divergence in potentials. The proposed sensor was successfully applied as an indicator electrode for the potentiometric titration of 1.0 × 10⁻² M Fe³⁺ ions with a 1.0 × 10⁻⁴ M EDTA and the direct determination of Fe³⁺ in mineral water and wastewater samples.     

Aluminium(III)-selective electrode based on a newly synthesized glyoxal-<Emphasis Type="Italic">bis</Emphasis>-thiosemicarbazone Schiff base

A PVC membrane electrode for Al³⁺ based on glyoxal-bis-thiosemicarbazone (GBTC) as an ion carrier was developed. The electrode exhibits a Nernstian slope of 20.1 mV per decade and a linear range of 1.8 × 10⁻⁵−1.0 × 10⁻¹ M for Al(NO₃)₃ with a detection limit of 8.7 × 10⁻⁶ M. It has a fast response time of about 10 s and can be used for at least 1 month. The proposed membrane sensor revealed a good selectivity for Al³⁺ over a wide variety of other metal ions and could be used in the pH range of 2.5–4.5. The text was submitted by the authors in English.     

A new lidocaine-selective membrane electrode based on its sulfathiazole ion-pair

A novel lidocaine ion-selective electrode is prepared, characterized and used in pharmaceutical analysis. The electrode incorporates PVC-membrane with lidocaine-sulfathiazole ion pair complex. The influences of membrane composition, temperature, pH of the test solution, and foreign ions on the electrode performance were investigated. The electrode showed a Nernstian response over a lidocaine concentration range from 1.0 ×10⁻⁵ to 1.0 × 10⁻¹ mol L⁻¹ with a slope of 60.1 ± 0.2 mV per decade at 25°C and was found to be very selective, precise, and usable within the pH range 5–9.5. The standard electrode potentials, E ^o, were determined at 10, 15, 20, 25, 30, 35 and 40°C, and used to calculate the isothermal temperature coefficient (dE ^o/dT=−0.0003 V °C⁻¹) of the electrode. However, the electrode performance is significantly decreased at temperatures higher than 45°C. The electrode was successfully used for potentiometric determination of lidocaine hydrochloride in pharmaceutical products. The article is published in the original.     

A novel chemically modified carbon paste electrode based on a new mercury(II) complex for selective potentiometric determination of bromide ion

A new modified carbon paste electrode based on a recently synthesized mercury (II) complex of a pyridine containing proton transfer compound as a suitable carrier for Br⁻ ion is described. The electrode has a linear dynamic range between 3.00×10⁻² and 1.0×10⁻⁵ M with a near-Nernastian slope of 61.0±0.9 mV per decade and a detection limit of 4.0×10⁻⁶ M (0.32 ppm). The potentiometric response is independent of the pH of the solution in the pH range 4.0–8.3. The electrode possesses the advantages of low resistance, fast response and good over a variety of other anions. It was applied as an indicator electrode in potentiometric titration of bromide ions and for the recovery of Br⁻ from tap water.     

Nickel,copper and manganese hexacyanoferrate with poly(3,4-ethylenedioxythiophene) hybrid film modified electrode for selectively determination of ascorbic acid

The NiHCF-PEDOT, CuHCF-PEDOT and MnHCF-PEDOT films were prepared on glassy carbon electrode (GCE) by multiple scan cyclic voltammetry and characterized using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and scanning electron microscope (SEM) techniques. The advantages of these films are demonstrated for selectivity detection of ascorbic acid using cyclic voltammetry and amperometric method. Interestingly, the NiHCF-PEDOT and CuHCF-PEDOT modified electrodes exhibited a wide linear response range (5 × 10⁻⁶−3 × 10⁻⁴ M, R ² = 0.9973 and 1.8 × 10⁻³−1.8 × 10⁻² M, R ² = 0.9924). The electrochemical sensors facilitated the oxidation of AA but not responded to other electroactive biomolecules such as dopamine, uric acid, H₂O₂, glucose. The difference is MnHCF-PEDOT/GCE that no response to AA. In addition, the NiHCF-PEDOT and CuHCF-PEDOT modified electrodes exhibited a distinct advantage of simple preparation, specificity, stability and reproducibility.     

Development of reliable analytical method for extraction and separation of thorium(IV) by Cyanex 272 in kerosene

A simple and selective spectrophotometric method has been developed for the extraction and separation of thorium(IV) from sodium salicylate media using Cyanex 272 in kerosene. Thorium(IV) was quantitatively extracted by 5 × 10⁻⁴ M Cyanex 272 in kerosene from 1 × 10⁻⁵M sodium salicylate medium. The extracted thorium(IV) was stripped out quantitatively from the organic phase with 4.0 M hydrochloric acid and determined spectrophotometrically with arsenazo(III) at 620 nm. The effect of concentrations of sodium salicylate, extractant, diluents, metal ion and strippants has been studied. Separation of thorium(IV) from other elements was achieved from binary as well as multicomponent mixtures such as uranium(VI), strontium(II), rubidium(I), cesium(I), potassium(I), Sodium(I), lithium(I), lead(II), barium(II), beryllium(II) etc. Using this method separation and determination of thorium(IV) in geological and real samples has been carried out. The method is simple, rapid and selective with good reproducibility (approximately ±2%).     

Platinum electrode coated with a bentonite–carbon composite as an environmental sensor for detection of lead

A Pt wire coated with a bentonite–carbon composite in a poly(vinyl chloride) membrane was used for detection of lead. The sensor has a Nernstian slope of 29.42±0.50 mV per decade over a wide range of concentration, 1.0×10⁻⁷ to 1.0×10⁻³ mol L⁻¹ Pb(NO₃)₂. The detection limit is 5.0×10⁻⁸ mol L⁻¹ Pb(NO₃)₂ and the electrode is applicable in the pH range 3.0–6.7. It has a response time of approximately 10 s and can be used at least for three months. The electrode has good selectivity relative to nineteen other metal ions. The practical analytical utility of the electrode is demonstrated by measurement of Pb(II) in industrial waste and river water samples.     

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.     

A novel lariat crown compound as ionophore for construction of a mercury(II)-selective electrode

Abstract  

The construction, performance, and application of a new PVC membrane electrode for determination of the mercury(II) ion, based on 8,17-bis(pyren-1-ylmethyl)-6,7,8,9,15,16,17,18-octahydrodibenzo[f,m][1,8,4,11]dithiadiazacyclotetradecine as an ionophore, is described. The effects of factors such as membrane composition, the nature and amount of the plasticizers and additives, and pH for the improved sensitivity of the electrode were studied. The electrode had a Nernstian response for mercury(II) ions over the concentration range 1.0 × 10⁻²–1.0 × 10⁻⁶ mol dm⁻³ with a slope of 27.6 ± 0.6 mV/pHg. The detection limit for mercury(II) was 7.9 × 10⁻⁷ mol dm⁻³. The response time of the electrode was between 5 and 15 s, depending on the concentration of mercury, and it can be used in a pH range 4.0–4.5 for approximately 4 months without any substantial divergence of the response characteristics. It showed higher selectivity for mercury(II) ions than for several common alkali, alkaline earth, and transition metal ions except silver(I). The proposed electrode was successfully applied to direct determination of mercury in a dental filling amalgam alloy as a real sample with a complex matrix and as an indicator electrode in complexation titrations.     

Synthesis of a charge-transfer complex of (1,3-diphenyldihydro-1H-imidazole)-4,5-dione dioxide with iodide and its application to the development of a highly selective and sensitive triiodide PVC-membrane electrode

In this paper, a novel membrane triiodide sensor based on a charge-transfer complex of (1,3-diphenyldihydro-1H-imidazole)-4,5-dionedioxime with iodine (CTCI) as a membrane carrier is introduced. The best performance was obtained with a membrane containing 30% polyvinylchloride (PVC), 63% dibutylphthalate (DBP), 5% CTCI, and 2% hexadecyltrimethylammonium bromide (HTAB). The electrode shows a Nernstian behavior (slope of 58.2 ± 0.3) over a very wide triiodide ion concentration range (5.0 × 10⁻⁸−1.0 × 10⁻² M), and has a low detection limit (4.0 × 10⁻⁸ M). The potentiometric response of the sensor is independent of pH of the solution in the pH range 3.0–9.0. The proposed sensor has a very low response time (<12 s) and a good selectivity relative to a wide variety of common inorganic and organic anions, including iodide, bromide, chloride, nitrate, sulfate, thiocyanate, monohydrogen phosphate, and acetate. In fact, the selectivity behavior of the proposed triiodide ion-selective electrode shows great improvements compared to the previously reported electrodes for triiodide ion. The proposed membrane sensor can be used for at least 6 months without any divergence in its potentials. The electrode was successfully applied as an indicator electrode in the titration of triiodide with thiosulfate ion. The text was submitted by the authors in English.