Potentiometric determination of mercury(II) and thiourea in strong acid solution using an ion-selective electrode with AgI-based membrane hydrophobised by PTFE

Summary The potentiometric determination of mercury(II) and thiourea (TU) in strong acid solution (pH 0–1) by using an all-solid-state ion-selective electrode with (Ag₂S 25%, AgI 25% and PTFE 50% m/m)-membrane is described. The linear response, 43 mV(pHg)^–1 and 80 mV(pTU)^–1, has been obtained in the concentration range from 10^–2 to under 10^–5 mol/l. By direct potentiometry at pH 0 mercury(II) can be determined in the presence of up to 10^–3 mol/l of iron(III). The change in potential in the tested concentration range of thiourea indicates the formation of Ag(TU) _1.4 ⁺ at the exposed surface of the membrane. This stoichiometry is in good agreement with that calculated from the average Ag/TU ratio in the potentiometric titration. The investigated electrode can be used as a good sensor for mercury(II) and thiourea in strong acid media and a wide variety of practical analytical systems.     

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.     

A potentiometric study of the oxidation of cobalt(II) with gold(III) chloride in presence of 1,10 phenanthroline or 2,2'-bipyridine : A new titration of cobalt (II) and its application to nickel-base alloys

The redox reaction between cobalt(II) and gold(III) chloride in the presence of 1.10-phenanthroline or 2,2'-bipyridine was studied, and a titration of the cobalt(II) complex with a gold(III) chloride solution was developed. A 4-fold amount of 1,10-phenanthroline or 2,2'-bipyridine was necessary for rapid quantitative reaction; the permissible pH range was 1.5–5. The oxidation of the cobalt(II) complex proceeds rapidly at 40–50°C, and a direct potentiometric titration was possible. The following maximum errors were obtained: 3.3% for 0.2–1.0 mg Co, 2.0% for 1–5 mg Co, and 0.70% for 10–40 mg Co. The following ions did not interfere: Ni(II), Zn(II), Pb(II), Cd(II), Mn(II), Fe(II), Cr(III), Al(III), Th(IV), Se(IV), Ti(IV), U(VI), Mo(VI), SO^2-₄ and PO^3-₄. Even small quantities of silver(I), copper(II), palladium(II), mercury(II)and iron(III) interfered. The method was applied to the determination of high cobalt contents in high-temperature nickel-base alloys.     

Simple and Selective Spectrophotometric Method for the Determination of Iron (III) and Total Iron Content, Based on the Reaction of Fe(III) with 1,2-Dihydroxy-3,4-Diketocyclo-Butene (Squaric Acid)

 Squaric acid (1,2-dihydroxy-3,4-diketo-cyclobutene) is used in a specific reaction with Fe(III) for the spectrophotometric determination of Fe(III) and total iron content. The optimization of the experimental parameters leads to the establishment of a simple, fast and accurate analytical method. The analytical procedure includes mixing ammonium squarate (40 mM), prepared in a phthalate buffer solution of pH 2.7, with the sample and measuring the absorbance at 515 nm. The molar absorptivity of the colored product is 3.95×10³ L·mol⁻¹·cm⁻¹, at 515 nm. Calibration graphs for Fe(III) are rectilinear for 0.5–20 mgL⁻¹, with a detection limit of 0.3 mgL⁻¹ and r.s.d. not exceeding 2.5%, for five replicates of a 3.0 mgL⁻¹ standard solution. The method has been successfully applied to the determination of iron (III) and the total iron content after quantitative oxidation of iron (II). The results for several analyzed samples when compared with those acquired by using the FAAS technique, were found to be in satisfactory agreement. Author for correspondence: University of Ioannina, Department of Chemistry, Laboratory of Analytical Chemistry, Ioannina 451 10, Greece. E-mail: panavelt@cc.uoi.gr Received July 27, 2002; accepted December 20, 2002 Published online April 11, 2003     

Natural monocrystalline pyrite as electrode material for potentiometric titrations in water

The possibility of applying natural monocrystalline pyrite as sensor for the potentiometric titration of acids in water was investigated. The potential of this electrode in aqueous solutions exhibits a sub-Nernst dependence. In fresh solutions the slope (mV/pH) is 33.9. The potential jumps at the titration end-point obtained in titrations of HCl, H(3)PO(4) and CH(3) COOH do not differ much from those obtained by the application of the glass electrode as the indicator one. The potentials in the course of the titration and at the titration end-point (TEP) are rapidly established. The results obtained in the determination of the investigated acids deviated for 0.16-0.34% with respect to those obtained by using the glass electrode as the indicator one.     

Mercury(II) ion-selective polymeric membrane sensor based on a recently synthesized Schiff base

A new polyvinyl chloride (PVC) membrane electrode that is highly selective to Hg(II) ions was prepared by using bis[5-((4-nitrophenyl)azo salicylaldehyde)] (BNAS) as a suitable neutral carrier. The sensor exhibits a Nernstian response for mercury ions over a wide concentration range (5.0×10⁻²-7.0×10⁻⁷ M) with a slope of 30±1 mV per decade. It has a response time of <10 s and can be used for at least 3 months without any measurable divergence in potential. The electrode can be used in the pH range from 1.0 to 3.5. The proposed sensor shows fairly good discriminating ability towards Hg²⁺ ion in comparison with some hard and soft metals. The electrode was used in the direct determination of Hg²⁺ in aqueous solution and as an indicator electrode in potentiometric titration of mercury ions.     

Development of a voltammetric method for the determination of iron(III) in Zn-Fe alloy galvanic baths

A square wave voltammetric method whith a static mercury drop electrode (SMDE) was developed for the quantitative determination of iron (III) in Zn-Fe alloy galvanic baths. Real alloy bath samples were analyzed by the standard addition method and recovery tests were carried out. 0.50 mol L^–1 sodium citrate (pH 6.0) or 0.20 mol L^–1 oxalic acid (pH 4.0) were applied as supporting electrolytes resulting in both cases in a peak potential of about –0.20 V vs. Ag|AgCl (saturated KCl). The iron (III) concentration in the alloy bath was 9.0 × 10^–4 mol L^–1. A good correlation (r = 0.9999) was achieved between the iron (III) concentration and the peak current in the electrolytes studied, with linear response ranges from 1.0 × 10^–6 to 1.2 × 10^–4 mol L^–1. Interference levels for some metals such as copper (II), lead (II), chromium (III) and manganese (II) that can hinder the Zn-Fe alloy deposition were evaluated; only copper (II) interferes seriously. Received: 4 April 2000 / Revised: 19 June 2000 / Accepted: 22 June 2000     

A novel ion selective membrane potentiometric sensor for direct determination of Fe(III) in the presence of Fe(II)

A new PVC membrane potentiometric sensor that is highly selective to Fe(III) ions was prepared by using 2-[(2-hydroxy-1-propenyl-buta-1,3-dienylimino)-methyl]-4-p-tolylazo-phenol [HPDTP] as a suitable carrier. The electrode exhibits a linear response for iron(III) ions over a wide concentration range (3.5 × 10⁻⁶ to 4.0 × 10⁻²) with a super Nernstian slope of 28.5 (±0.5) per decade. The electrode can be used in the pH range from 4.5 to 6.5. The proposed sensor shows fairly a good discriminating ability towards Fe³⁺ ion in comparison to some hard and soft metals such as Fe²⁺, Cd²⁺, Cu²⁺, Al³⁺ and Ca²⁺. It has a response time of <15 s and can be used for at least 2 months without any measurable divergence in response characteristics. The electrode was used in the direct determination of Fe³⁺ in aqueous samples and as an indicator electrode in potentiometric titration of Fe(III) ions.     

Potentiometric titration of Co(II) in presence of Co(III)

A potentiometric titration for cobalt(II) determination in the presence of Co(III) based on the oxidation of Co(II) with Na₂CrO₄ in ethylenediamine medium and back-titration of the oxidant excess with (NH₄)₂Fe(SO₄)₂ in acid medium is described. The titration is monitored with a Pt indicator electrode and carried out until the greatest jump of potential from one drop of titrant appears. A RSD smaller than 1.5% has been obtained for 50–300 μmol Co(II). The method proposed was applied in the analysis of a new type electroless copper plating solutions containing Co(II)-ethylenediamine complex compounds as reducing agents. Cu(II), Co(III) and Cr(III) do not interfere in the determination of Co(II).     

Silica-modified electrode for the selective detection of mercury

Pure silica particles were dispersed within carbon paste and the resulting modified electrode was applied to the selective voltammetric detection of mercury(II) species after their accumulation at open circuit. The remarkable selectivity observed between pH 4 and 7 was attributed to the intrinsic adsorption mechanism which involves a condensation reaction between mercury(II) hydroxide and hydroxyl groups on the silica surface, leading to the formation of an inner-sphere-type surface complex. After optimization with respect to the electrode composition, the detection medium, and the voltammetric scan mode, a linear response was obtained in the concentration range between 2 × 10⁻⁷ M to 1 × 10⁻⁵ M, by applying anodic stripping square wave voltammetry. Various silica samples were used and their sorption behavior was discussed in relation to their specific surface area and porosity. The effect of chloride and pH on the accumulation of mercury(II) on silica was also investigated. Received: 4 September 1999 / Accepted: 5 January 2000     

Fluorescence enhancement assay for trace iron(II) using Pyr-tempo as a spin label fluorescent probe

Pyrene-tetramethylpiperidinyl (Pyr-Tempo) as a spin label fluorescent probe for iron(II) was synthesized. It exhibited weak fluorescence (λ_exc/λ_em = 346/399 nm) in aqueous solution due to an intramolecular quenching pathway. A method for determination of iron(II) was proposed based on the fluorescence enhancement of the probe in the presence of iron(II) in acidic medium. Under optimum conditions, the fluorescence enhancement of Pyr-Tempo is linearly proportional to the iron(II) concentration range of 6.0 × 10⁻⁸ to 9.6 × 10⁻⁶ mol L⁻¹ with a detection limit of 8.0 × 10⁻⁹ mol L⁻¹. The relative standard deviation (RSD) of six replicate measurements is 1.95% for 3.0 × 10⁻⁷ mol L⁻¹ iron(II). The developed spin label fluorescence probe is found to be rapidly and sensitively responsive to iron(II) with high selectivity compared to existing fluorescence methods. The proposed method was successfully applied to iron(II) detection in five real samples with satisfactory results obtained by manual UV/Vis spectrophotometry (standard method) with 1,10-phenanthroline.     

Solid-contact Cu(II) ion-selective electrode based on 1,2-di-(<Emphasis Type="Italic">o</Emphasis>-salicylaldiminophenylthio)ethane

The development of Cu(II) solid-contact ion-selective electrodes, based on 1,2-di-(o-salicylaldiminophenylthio)ethane as a neutral carrier, is presented. For the electrodes construction, unmodified carbon ink (type 1 electrode) and polymer membrane-modified carbon ink (type 2 electrode) were used as solid support and transducer layer. Also, carbon ink composite polymer membrane electrode (type 3 electrode) was prepared. The analytical performance of the electrodes was evaluated with potentiometry, while bulk and interfacial electrode features were provided with electrochemical impedance spectroscopy. It is shown that modification of carbon ink with polymer membrane cocktail decreases the bulk contact resistance of the transducer layer and polymer membrane, thus enhancing the analytical performance of the electrode in terms of sensitivity, linear range, and stability of potential. The optimized electrodes of types 2 and 3 exhibit a wide linear range with detection limits of 1.8 × 10⁻⁶ and 1.6 × 10⁻⁶ M, respectively. They are suitable for determination of Cu²⁺ in analytical measurements by direct potentiometry and in potentiometric titrations, within pH between 2.3 and 6.5. The electrodes are selective for Cu²⁺ over a large number of tested transition and heavy metal ions.     

The electrochemical behaviour of tris(N,N-disubstituted dithiocarbamato) complexes of ruthenium(III) in dimethylsulphoxide

The reduction at the mercury electrode of a series of ruthenium(III) dithiocarbamates in dimethylsulphoxide (DMSO) has been investigated using D.C. A.C. polarography, chronoamperometry, coulometry (controlled potential electrolysis) and cyclic voltammetry. Tris(N,N-disubstituted dithiocarbamato) complexes of ruthenium exhibit two one-electron polarographic waves in the potential range 0.00 to 2.20 volt relative to Ag/AgClO₄ (DMSO) reference electrode. The first reduction, at approximately — 0.950 volt, is quasi-reversible. The [Ru(II) (dAdtc)₃]⁻ complexes resulting from this reduction are susceptible to dissociation, releasing the free dialkyldithiocarbamate anion.     

Potentiometric Determination of Menadione (Vitamin K3)

 The construction and electrochemical response characteristics of poly(vinyl) chloride matrix membrane sensors for menadione (vitamin K₃) are described. Membranes incorporating the ion association complexes of menadione anion with bathophenanthroline nickel(II) and iron(II) as electroactive materials show linear response for menadione over the range 10⁻¹–10⁻⁵ M with anionic slopes of 58.2–51.4 mV per concentration decade. Both sensors exhibit fast response time (20–30 s), low detection limit (2 × 10⁻⁵ M), good stability (4–6 weeks) and selectivity coefficient (10⁻¹–10⁻³). Direct potentiometric determination of menadione under static and hydrodynamic mode of operations shows average accuracies of 98.8 and 98.5% with relative standard deviations of 0.6% and 1.3%, respectively. Application of the method for the determination of menadione in human plasma gives favourable results compared with those obtained by the standard spectrophotometric method. Received February 26, 2001. Revision October 1, 2001.     

Regularities of the formation of iron(III) nanocrystalline particles during the oxidation of iron(II) compounds in a neutral medium

The regularities of the formation of iron(III) oxide hydroxides as nanocrystalline particles via oxidation of iron(II) compounds in a near-neutral pH region were studied by potentiometric titration, electron microscopy, chemical analysis, and X-ray diffraction. The oxidation process comprises two steps. The first step produces Fe(II)-Fe(III) hydroxo salts having a “green rust” structure in the form of nanocrystalline particles shaped as hexagons. The second step produces anisotropic nanocrystalline particles of iron(III) oxide hydroxides via the dissolution-oxidation-precipitation mechanism and via solid-phase oxidation. The oxidation of chlorine-containing suspensions helps the formation of single-phase nanocrystalline lepidocrocite, while oxidation in the presence of sulfate ions yields nanocrystalline goethite.     

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.     

Applications,involving the iodide ion: VIII. Direct and indirect determination of mercury(I) and analysis of mixtures. Analysis of chromium(VI)-chromium (III) mixtures. Determination of hypochlorite

Mercury(I), down to 3 ppm, has been accurately determined by direct titration with iodide or by back-titrating excess of iodide with mercury (II) using silver amalgam as the indicator electrode. The direct method and additional volumetric ones were applied to the rapid analysis of various mixtures involving mercury(I) with fair accuracy and precision. Analysis of Cr(VI)-Cr(III) mixtures involved potentiometric back-titration of excess iodide and of excess EDTA separately with mercury(II). Back-titration of excess iodide was successfully applied to the determination of hypochlorite.     

Voltammetric behavior of the iron(II)-(III) and cerium(III)-(IV) couples in potentiometric titrations at constant current and amperometric titrations with two indicator electrodes

The voltammetric behavior at the rotated platinum electrode of the iron(II)-(lII) and cerium (III)-(IV) couples in sulfuric and hydrochloric acids has been investigated The iron and cerium couples are not reversible at a platinum electrode when current flows in the system, and the current-potential curves deviate considerably from those predicted on the basis of reversibility Titration curves for potentiometric titrations at constant current using one and two indicator electrodes are predicted from the current-potential curves and compared with the experimental curves.The degree of reversibility of the iron couple depends greatly on the pretreatment of the electrode The current-potential curves of the iron couple at a platinum electrode coated with a monomolecular film of platinum oxide approach reversibility while those at a clean electrode are highly irreversible Experimental and calculated titration lines for amperometric titrations using two indicator electrodes are compared, and the effects of medium and applied e.m.f. upon the characteristics of the titration curves are considered.     

Complexation between iron(III) and nicotinamide in aqueous dimethyl sulfoxide

The stability constants of iron(III) complexes with nicotinamide in water-DMSO mixtures (X _DMSO = 0–0.75) were determined by potentiometric titration at 25.0 ± 0.1°C and an ionic strength of 0.25 (NaClO₄). The contributions from the solvation of the reagents to the Gibbs energy of complexation transfer were analyzed. The stabilities of iron(III), copper(II), and silver(I) complexes with nicotinamide were compared. The observed decrease in the stability constants was attributed to the stabilization of iron(III) solvate complexes as the DMSO content increases.     

Copper Incorporated [Me2(15)dieneN4] Macrocyclic Complex for Fabrication of PVC based Membrane Electrode for Copper

Copper (II) complex of 2,4-dimethyl-1,5,9,12-tetraazacyclopentadeca-1,4-diene, [Me₂(15)dieneN₄] was synthesized and used in the fabrication of Cu²⁺ – selective ISE membrane in PVC matrix. The membrane having Cu(II) macrocyclic complex as electroactive material along with sodium tetraphenyl borate (NaTPB) as anion discriminator. Dibutyl phthalate (DBP) as plasticizer in poly(vinyl chloride) (PVC) matrix was prepared for the determination of Cu²⁺. The best performance was observed by the membrane having Cu(II) complex–PVC–NaTPB–DBP with composition 1:5:1:3. The sensor worked well over a concentration range 1.12 × 10⁻⁶ M–1.0 × 10⁻¹ M between pH 2.1–6.2 and a fast response time 10±2 s and a lifetime of 6 months. Their performance in partially non-aqueous medium was found satisfactory. Electrodes exhibited excellent selectivity for Cu²⁺ ion over other mono-, di-, trivalent cations. It can also be used as indicator electrode in the potentiometric titration of Cu²⁺ against EDTA as well as in the determination of Cu²⁺ in real samples.