Novel Dicyanoargentate Polymeric Membrane Sensors for Selective Determination of Cyanide Ions

The construction and general performance characteristics of three novel potentiometric PVC membrane sensors responsive to dicyanoargentate anion are described. The sensors are based on the use of magnesium(II)‐ and iron(II)‐phthalocyanines as neutral ionophores and iron(II)‐bathophenanthroline dicyanoargentate ion‐pair complex as an ion exchanger in plasticized PVC matrices. These sensors exhibit fast, stable and near‐Nernstian response (54–59 mV/decade) for the singly charged dicyanoargentate anion over the concentration range 1×10^?2–5.8×10^?6 M. Potentiometric responses of sensors based on metal phthalocyanines and iron(II)‐bathophenanthroline are stable over the pH ranges 5–7 and 5–12, respectively. The selectivity of the sensors are fairly good over most common anions. Use of the sensors for potentiometric determination of microgram quantities of cyanide ion after conversion into dicyanoargentate anions shows an average recovery of 99.5% and a mean standard deviation of ±0.5%. Determination of cyanide ions in some exhausted electroplating bath samples gives results that compare favourably well with data obtained using the solid‐state cyanide electrode.     

Voltammetric determination of mercury(II) at a carbon paste electrode in aqueous solutions containing tetraphenylborate ion

The determination of mercury(II) ions can be achieved by monitoring the decrease in the oxidation peak of the tetraphenylborate ion in the presence of this metal ion at a carbon paste electrode. The reaction between mercury(II) and the tetraphenylborate ion results in the formation of diphenylmercury, thus providing the method with good selectivity over other metal ions. Using anodic stripping voltammetry in a neutral electrolyte, a linear dependence of the decrease of peak height was observed on increasing the mercury(II) concentration in the range 1 x 10(-6)-8 x 10(-9)M mercury(II). Zinc(II), cadmium(II), lead(II), nickel(II), cobalt(II), tin(II), potassium(I) and ammonium(I) ions did not interfere at a 1000-fold concentration excess. Iron(III) and chromium(III) did not interfere at a 250-fold and 50-fold concentration excess, respectively. Following masking procedures, copper(II), bismuth(III) and silver(I) did not interfere at a 100-fold concentration excess. The method can be used to determine the concentration of mercury(II) in natural waters contaminated by this metal.     

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.     

Ion-selective chalcogenide electrodes for a number of cations

Ion-selective chalcogenide disc electrodes have been developed which are responsive to cations such as silver, lead, chromium(III), nickel, cobalt(II), cadmium, zinc, copper(II) and manganese(II) ions. Each was prepared by using the corresponding metal chalcogenide with silver sulphide. An electrode was assembled with both a compacted and a sintered disc. The sintered electrodes were more sensitive and stable than the compacted ones. Response to silver ion was 59.5 mV pAg , to lead, nickel, cadmium, zinc and copper(II) 29.5 mV pM and to chromium(III) 20 mV pM . Cobalt(II) and manganese(II) electrodes had a non-Nernstian response of 25 mV pM . Both selenides and tellurides can be used for potentiometric determination, but the manganese(II) electrode serves as an analytical tool only when the disc consists of manganese(II) telluride and silver sulphide.     

Novel PVC-based copper(II) membrane sensor based on 2-(1'-(4'-(1'-hydroxy-2'-naphthyl)methyleneamino)butyl iminomethyl)-1-naphthol.

A copper(II) ion-selective PVC membrane sensor based on 2-(1'-(4'-(1'-hydroxy-2'-naphthyl)methyleneamino)butyl iminomethyl)-1-naphthol (BHNB) as a novel Schiff base containing a sensing material has been successfully developed. The sensor exhibits a good linear response of 29 mV per decade within the concentration range of 10(-1)-10(-6) M of Cu2+. The sensor shows good selectivity for copper(II) ion in comparison with alkali, alkaline earth, transition and heavy metal ions. The BHNB-based sensor is suitable for use with aqueous solutions of pH 3.5-7.0 and displays minimal interference by Sr(II), Cd(II), Hg(II), Zn(II) and Pb(II), which are known to interfere with other previously suggested electrodes. The proposed membrane electrode was used as a sensor for determining the Cu(II) content in black tea samples. It was also applied as an indicator electrode in the potentiometric titration of Cu2+ ions with EDTA.     

Application of a Zeolite-Poly(vinyl chloride) Electrode to Potentiometric Studies of Alkali Metal Ions

Potentiometric electrodes based on the incorporation of zeolite particles into poly(vinyl chloride) (PVC) membranes are described. The electrode characteristics are evaluated regarding the response towards alkali ions. PVC membranes plasticized with dibutyl phthalate and without lipophilic additives (co-exchanger) are used throughout this study. The electrode exhibits a Nernstian response over the alkali metal cation concentration range of 1.0 × 10^?4 to 1.0 × 10^?1 M with a slope of 57.0 ± 0.9 mV per decade of concentration with a working pH range 3.0–9.0 and a fast response time of ≤15 s. The selectivity coefficients for cesium ion as test species with respect to alkaline earth, ammonium, and some heavy metal ions are determined. The proposed zeolite-PVC electrode is applied to the determination of ionic surfactant.     

Self‐Assembled Mercapto‐Compound‐Gold‐Nanoparticle‐Modified Carbon Paste Electrode for Potentiometric Determination of Cadmium(II)

A new modified carbon paste electrode (CPE) based on a recently synthesized ligand [2‐mercapto‐5‐(3‐nitrophenyl)‐1,3,4‐thiadiazole] (MNT), self‐assembled to gold nanoparticles (GNP) as suitable carrier for Cd(II) ion with potentiometric method are described. The proposed electrode exhibits a Nernstian slope of 29.4±1.0 mV per decade for Cd(II) ion over a wide concentration range from 3.1×10^?8 to 3.1×10^?4 mol L^?1. The detection limit of electrode was 2.0×10^?8 mol L^?1 of cadmium ion. The potentiometric responses of electrode based on MNT is independent of the pH of test solution in the pH range 2.0–4.0. It has quick response with response time of about 6 s. The proposed electrode show fairly good selectivity over some alkali, alkaline earth, transition and heavy metal ions. Finally, the proposed electrode was successfully employed to detect Cd(II) ion in hair and water samples.     

Effect of metal ions on the response of a cyanide-selective electrode

An extended model and its experimental verification are presented for the response of a cyanide-selective electrode in the presence of metal ions. The model takes into account the effect of metal-hydroxide complexes ar high pH values. The electrode responds to the total cyanide concentration even in the presence of an excess of zinc and cadmium ions. When copper(I) is present, the cyanide complexes must be decomposed before the total cyanide concentration can be measured. The results show the importance of considering both metal-cyanide and the metal-hydroxide complexation.     

Simultaneous determination of lead,copper, and mercury at a modified carbon paste eletrode containing humic acid

The modified carbon paste electrode (CPE) responding simultaneously to lead(II), copper(II), and mercury(II) ions has been constructed by incorporating humic acid (HA) into the graphite powder with Nujol oil. Simple immerging of the electrode into the measuring solution containing these metal ions led to the chemical deposition of the ions onto the electrode through the complexation of the ions with HA. Cyclic and differential pulse voltammetry (DPV) characterized the modified electrode's surfaces. Several cyclings of the potential regenerated the electrode (from more positive than the stripping potential of reduced Hg to more negative than the reduction of Pb(II)ion), which was then used for another deposition. After five deposition/measurement/regeneration cycles, the peak current of voltammograns of the analyte decreased slightly. The response reproduced with a 5.1% relative standard deviation. We also applied ihe differential pulse technique to the previously mentioned system. Here, the detection limit tor Pb(II), Cu(II), and Hg(II) ions were 5.0 × 10⁻⁹ M 8.0 × 10⁻⁹ M, and 8.0 × 10⁻⁹ M, respectively, for 20 minutes of deposition time. After pretreatment of silver(I) ion with KC1, we could not observe any interference by other metal ions on the determination of the test ions in aqueous solution. Satisfactory results were acquired for the determination of the test metal ions in certified standard urine reference material SRM's 2670 (trace elements in urine).     

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.     

Influence of cyanide and sulphide ions on the reduction and reoxidation of cobalt(II) in thiocyanate solution at mercury electrodes

The process of reduction and reoxidation of cobalt(II) in thiocyanate solution at hanging mercury drop electrode has been investigated by cyclic voltammetric, chronoamperometric and anodic stripping methods. In 0.1 M NaSCN and 0.4 M NaClO₄ solution containing 1×10^?3M cobalt(II), the voltammogram on the first cycle at 0.05 V s^?1 gives a cathodic peak at ?1.06 V with hysteresis on reversal, and an anodic wave with a peak potential of ?0.28 V and with two shoulders near ?0.38 and ?0.45 V, respectively. Multicyclic voltammograms under the same conditions give a cathodic peak at ?0.90 V and an anodic peak at ?0.45 V. The reduction and reoxidation of cobalt(II) in thiocyanate solution is accelerated by the reduction products of thiocyanate ion, cyanide and sulphide ions, which are produced during the electroreduction of cobalt(II).A mechanism of reduction and reoxidation of cobalt(II) which involves a chemical reduction of thiocyanate ion by electroreduced metallic cobalt and takes into account cyanide and sulphide ions is proposed. The hysteresis on the cathodic wave is caused by the difference in reduction potentials of cobalt(II)-thiocyanate and-cyanide complexes. Cyclic voltammetric study of cobalt(II) in perchlorate solution containing trace amounts of cyanide and sulphide ions supports these conclusions.     

Investigation of Copper(II) Interference on the Anodic Stripping Voltammetry of Lead(II) and Cadmium(II) at Bismuth Film Electrode

The bismuth‐coated electrode is known to be prone to errors caused by copper(II). This study investigates copper(II) interference at bismuth film electrode for the detection of lead(II) and cadmium(II). It was conducted using glassy carbon electrode, while the bismuth film was plated in situ simultaneously with the target metal ions at ? 1200 mV. Copper(II) presented in solution significantly reduced the sensitivity of the electrode, for example there was an approximately 70 % and 90 % decrease in peak signals for lead(II) and cadmium(II), respectively, at a 10‐fold molar excess of copper(II). The decrease in sensitivity was ascribed to the competition between copper and bismuth or the metal ions for surface active sites. Scanning electron microscopy (SEM) and energy dispersive X‐ray (EDX) analysis suggested a large decrease in the amount of bismuth nanoparticles formed on the electrode surface in the presence of copper(II) occurred, validating the competition between copper and bismuth ions for surface active sites. Recovery of the stripping signal of lead(II) and cadmium(II) was obtained by adding ferrocyanide ion to the solution. Finally, the proposed method was successfully applied to determine lead(II) and cadmium(II) in water samples and the method was validated by ICP‐MS technique.     

Used gold nano-particles as an on/off switch for response of a potentiometric sensor to Al(III) or Cu(II) metal ions

The potentiometric response of a carbon paste electrode modified with silica sol-gel and mercaptosuccinic acid (MSA) in the presence and absence of gold nano-particles was studied. The results showed that the electrode with gold nano-particles was responded to Al(3+) ions as a hard metal ion. On the other hand, the electrode without gold nano-particles was responded to copper ions as a soft metal ion. The electrodes without and with gold nano-particles exhibits a Nernstian slope of 29.1 and 19.2 mV decade(-1) for copper and aluminum ions over a wide concentration range of 4.3×10(-7)-1.0×10(-2) and 4.5×10(-7)-1.6×10(-3) mol L(-1), respectively. The detection limits of electrodes were 4.0×10(-7) and 1.6×10(-7) mol L(-1) for copper and aluminum ions, respectively.     

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.     

Bifunctional potentiometric sensor based on MoO3 nanorods

A solid-phase film electrode with an ion-sensitive membrane based on MoO₃ nanorods was developed. Depending on the pH of test solution, the proposed electrode can be used as a sensor for measuring the concentration of hydrogen or alkali metal ions. In the range of 1 ≤ pH ≤ 5, the electrode reacts to changes in the concentration of hydrogen ions with an electrode response slope of 54 ± 2 mV/pH. The electrode is selec- tive to alkali metal cations in the concentration ranges of $0 \leqslant pc_{M^ + } \leqslant 4$ for M = Na, K, and Li and $1 \leqslant pc_{M^ + } \leqslant 5$ for M = Rb and Cs and the solution acidity 5 ≤ pH ≤ 13.5 with a nearly theoretical slope. The selectivity coefficients of the electrode to the ions of Na(I), Rb(I), Cs(I), Mg(II), Ca(II), Sr(II), and Ba(II) were determined.     

Ion-selective electrodes based on silver sulphide

A series of electrodes with membranes of silver sulphide have been prepared. Their standard potentials and their response to sulphide and silver ions are measured and compared with those of a single-crystal silver sulphide electrode. The selectivity parameters against heavy metal ions and halides, as well as cyanide, are discussed. It is concluded that only interferences from cyanide ions and mercury(II) ions are detrimental to the practical use of the electrodes for measuring pAg and pS.     

Preconcentration and determination of mercury(II) at a chemically modified electrode containing 3-(2-thioimidazolyl)propyl silica gel.

A mercury-sensitive chemically modified graphite paste electrode was constructed by incorporating modified silica gel into a conventional graphite paste electrode. The functional group attached to the (3-chloropropyl) silica gel surface was 2-mercaptoimidazole, giving a new product denoted by 3-(2-thioimidazolyl)propyl silica gel, which is able to complex mercury ions. Mercury was chemically adsorbed on the modified graphite paste electrode containing 3-(2-thioimidazolyl)propyl silica (TIPSG GPE) by immersion in a Hg(II) solution, and the resultant surface was characterized by cyclic and differential pulse anodic stripping voltammetry. One cathodic peak at 0.1 V and other anodic peak at 0.34 V were observed on scanning the potential from -0.1 to 0.8 V (0.01 M KNO3; v = 2.0 mV s(-1) vs. Ag/AgCl). The anodic peak at 0.34 V show an excellent sensitivity for Hg(II) ions in the presence of several foreign ions. A calibration graph covering the concentration range from 0.02 to 2 mg L(-1) was obtained. The detection limit was estimated to be 5 microg L(-1). The precision for six determinations of 0.05 and 0.26 mg L(-1) Hg(II) was 3.0 and 2.5% (relative standard deviation), respectively. The method can be used to determine the concentration of mercury(II) in natural waters contaminated by this metal.     

High-performance liquid chromatography of micelle-solubilized complexes-IV Reversed-phase ion-pair chromatography of metal-3,5-diBr-PADAP-Triton X-100 complexes

The micellar solubilization complex systems of V(V), Cu(II), Zr(IV), Pd(II), Fe(III), Ni(II) and Co(II) with 3,5-diBr-PADAP and Triton X-100 have been investigated by HPLC on an ODS (5 x 250 mm) column with a ternary eluent of methanol-acetone-acetone-water containing TBA(+) and acetate buffer (pH 3.0) at 600 or 572 nm wavelength for the detection of the complexes. An HPLC-spectrophotometric method for determination of seven metal ions has been developed. The peak height calibration curves are linear up to 50-100 mu/1, metal ion concentration. The relative standard deviations for the determination of 30.0 mu/1 metal ion were 0.9-1.6% and the detection limits (S/N = 3) were 1.1-3.6 mug/1.     

Copper(II)-selective electrode using 2,2'-dithiodianiline as neutral carrier

Poly(vinyl chloride) membrane electrode, that is highly selective and sensitive to Cu(II) ions, was developed by using 2,2'-dithiodianiline and dibutyl phthalate as carrier and plasticizer, respectively. The electrode exhibits good potentiometric response for Cu(II) over a wide concentration range (5.0x10(-2)-7.0x10(-7) mol l(-1)) with Nernstian slope of 30+/-1 mV per decade. The response time of the electrode is 10 s and it has been used for a period of one month and exhibits good selectivity towards Cu(2+) in comparison to alkali, alkaline earth, transition and heavy metal ions, with no interference caused by Pb(2+), Cd(2+) and Fe(+2) which are known to interfere with many other copper electrodes.     

Lead(II) ion-selective electrode based on polyaminoanthraquinone particles with intrinsic conductivity

A new polyvinylchloride membrane electrode was facilely prepared by using polyaminoanthraquinone (PAAQ) microparticles with an intrinsically electrical conductivity as a lead(II) ionophore. It is found that the electrode performance will significantly be improved with adding 1 wt% PAAQ microparticles and decreasing the membrane thickness. A 90 μm-thick membrane electrode consisting of PAAQ(salt):polyvinyl chloride:dioctylphthalate:sodium tetraphenylborate of 1:33:66:1 (wt) but without any traditional lead(II) ionophore achieved the optimal performance and exhibited a good Nernstian response for Pb(II) ions over a wide concentration range from 2.5 × 10⁻⁶ to 0.1 M with a slope of 28.9 mV/decade and a detection limit down to 776 nM. A reasonably short response time of 12 s was revealed together with a long lifetime over a period of around 4 months in a wide pH range between 2.8 and 5.2. A fixed interference method indicated that the electrode has an excellent selectivity for lead(II) ion over alkali, alkaline earth and other heavy metal ions. The proposed electrode has been also found to be a powerful indicator electrode for potentiometric titration of Pb(II) ions with EDTA. The electrode can be used to accurately monitor the Pb(II) pollution in environmental waters.