Book reviews

Inorganic mercury ions (Hg²⁺) in laboratory prepared solutions were determined with a screen-printed carbon electrode (SPCE) coated with a polyaniline-methylene blue (PANI-MB) polymer layer. The structure and properties of the PANI-MB polymer layer were compared to that of normal polyaniline (PANI) in order to elucidate the structure of the PANI-MB layer. The electrically-conducting polymers were prepared by electrochemical polymerisation of monomer solutions of aniline, and mixed solutions of aniline with methylene blue onto respective screen-printed carbon electrodes (SPCEs). Scanning Electron Microscopy (SEM) analyses of the SPCE polymer coated electrodes have shown that nanostructured materials have formed with the diameters of the PANI nanoclusters and PANI-MB nanorods at approximately 200 nm. Anodic stripping voltammetry (ASV) was used to evaluate a solution composed of 1 × 10^?6 M Hg²⁺, in the presence of the SPCE/PANI-MB polymer sensor electrode. The Hg²⁺ ions were determined as follows: (i) pre-concentration and reduction on the modified electrode surface and (ii) subsequent stripping from the electrode surface during the positive potential sweep. The experimental conditions optimised for Hg²⁺ determination included the supporting electrolyte concentration and the accumulation time. The results obtained have shown that the SPCE/PANI-MB polymer sensor electrode operates optimally at a pH 2, with the supporting electrolyte concentration at 0.5 M HCl. A linear calibration curve was found to be in the range of 1 × 10^?8 M to 1 × 10^?5 M Hg²⁺ after 120 s of pre-concentration. The detection limit was calculated and found to be 54.27 ± 3.28 µg L^?1 of Hg²⁺. The results have also shown that a conducting polymer modified SPCE sensor electrode can be used as an alternative transducer for the voltammetric stripping and analysis of inorganic Hg²⁺ ions.     

Copper(II) ion sensor based on electropolymerized undoped conducting polymers

A solid state copper(II) ion sensor is reported based on the application of electropolymerized undoped (neutral) polycarbazole (PCz) and polyindole (PIn) modified electrodes. The new sensor shows high selectivity to Cu²⁺ ions with a detection limit of 10^–5 M. PCz and PIn are formed respectively by the anodic oxidation of 50 mM carbazole and 5 mM indole monomers in dichloromethane containing 0.1 M tetrabutylammonium perchlorate on a platinum electrode using a single compartment cell. Potentiostatic polymerization of both the monomers are carried out at 1.3 V and 1.0 V vs. Ag/AgCl, respectively. Perchlorate ions were electrochemically removed from the polymer films by applying – 0.2 V vs. Ag/AgCl. Polymer-coated electrodes are incubated in 1 M KCl solution for 8 h followed by incubation in distilled water for 2 h before using as a metal ion sensor. The undoped PCz and PIn electrodes were found to be highly selective and sensitive for Cu²⁺ ions with little selectivity for Pb²⁺ and negligible response towards Ag⁺, Hg²⁺, Cu⁺, Ni²⁺, Co²⁺, Fe²⁺, Fe³⁺ or Zn²⁺. Potentiometric responses for Cu²⁺ ions are recorded for both the sensor electrodes together with a double-junction Ag/AgCl reference electrode. Calibration curves for Cu²⁺ are reported for both ion sensors. The polymer-modified electrodes were found to be stable for several weeks. Electronic Publication     

New Methylene Blue (NMB) Encapsulated in Mesoporous AlMCM‐41 Material and Its Application for Amperometric Determination of Ascorbic Acid in Real Samples

New methylene blue (NMB) dye incorporated into AlMCM‐41 surfactant‐free and hybrid surfactant‐AlMCM‐41 mesophase. UV‐vis evidence shows that new methylene blue dye protonated in both cases of zeolites. New methylene blue is electroactive in zeolites and their electrochemical activity has been studied by cyclic voltammetry and compared to that of NMB in aqueous solutions. New methylene blue molecules are not released to the solution during CV measurements and are accessible to H₃O⁺ ions. The presence of surfactant affects the kinetics of the redox process through proton ions diffusion. The midpoint potentials (E_m) values show that new methylene blue dye incorporated into AlMCM‐41 can be reduced easily with respect to solution new methylene blue. New methylene blue interacting with surfactant polar heads and residual Br^? ions as a results, it shows a couple of peaks in high potential with respect to new methylene blue solution. The electrode made with methylene blue‐AlMCM‐41 without surfactant was used for the mediated oxidation of ascorbic acid. The anodic peak current observed in cyclic voltammetry was linearly dependent on the ascorbic acid concentration. The calibration plot was linear over the ascorbic acid concentration range 1.0×10^?5 to 5.0×10^?4 M. The detection limit of the method is 1.0×10^?5 M, low enough for trace ascorbic acid determination in various real samples.     

Electrochemical Preparation of Brilliant‐Blue‐Modified Poly(diallyldimethylammonium Chloride) and Nafion‐Coated Glassy Carbon Electrodes and Their Electrocatalytic Behavior Towards Oxygen and L‐Cysteine

Brilliant blue FCF‐modified glassy carbon electrodes have been prepared by cycling the Nafion (or poly(diallyldimethylammonium chloride) (PDDAC)) coated electrodes repeatedly 15 cycles in brilliant blue FCF (BB FCF) dye solution. The BB FCF molecules are incorporated into Nafion coating by cycling the film‐covered electrode between +0.3 to 1.2 V (vs. Ag/AgCl) in pH 1.5 BB FCF solution while PDDAC‐coated electrode cycled between 0 to ?1.0 V (vs. Ag/AgCl) in pH 6.5 BB FCF solution to immobilize the dye. Electrostatic interaction between dye molecule and PDDAC was predominant in PDDAC coating whereas immobilization of dye in Nafion film attributed to the combined effect of electrostatic and hydrophobic interactions. The voltammetric features of BB FCF‐modified electrodes resemble that of surface‐confined redox couples. The peak potentials of BB FCF‐incorporated PDDAC‐coated electrode were shifted to more positive potential region with decreasing pH of contacting solution. BB FCF‐modified electrodes showed electrocatalytic activity towards reduction of oxygen and oxidation of L ‐cysteine with significant decease of overvoltage compared to unmodified electrode. The BB FCF‐modified Nafion‐coated electrode was tested for its analytical applications toward determination of L ‐cysteine. The linear range of calibration plot at BB FCF‐modified Nafion‐coated electrode is 10 to 100 μM, which coincides with L ‐cysteine levels in biological fluids. Sensitivity and detection limit of the electrode are 111 nA μM^?1 and 0.5 μM, respectively.     

Colorimetric chemosensor for Fe<Superscript>2+</Superscript> and Fe<Superscript>3+</Superscript> based on a ternary mixture of an anionic dye,a cationic polyelectrolyte,and a metal chelator in aqueous solution

A new colorimetric chemosensor based on a simple ternary mixture of an anionic dye, pyrogallol red (PR), a cationic polyelectrolyte, poly(diallyldimethylammonium chloride) (PDADMAC), and a metal chelator, N-(2-hydroxyethyl) ethylenediaminetriacetic acid (HEDTA) for the colorimetric detection of Fe²⁺ and Fe³⁺ has been developed in an aqueous solution buffered at pH 5. Upon addition of Fe²⁺ or Fe³⁺ to the mixture, the absorption spectra showed a bathochromic shift; correspondingly, the solution color changed from red to blue, whereas other metal ions basically resulted in insignificant spectral and color changes. From the competitive experiments, no obvious interferences for the colorimetric detection of Fe²⁺ and Fe³⁺ were observed in the presence other metal ions. The results indicated that the mixture could be used as a potential Fe²⁺ and Fe³⁺ colorimetric and naked eye chemosensor in aqueous media. This research demonstrates that the ternary ensemble consisted of an organic dye, an oppositely charged polyelectrolyte, and a metal chelator is a versatile and convenient tool for the facile preparation of a novel chemosensor system.     

Determination of hydrogen peroxide in pickling baths for copper alloys by linear sweep voltammetry

Hydrogen peroxide in pickling baths for copper and copper alloys can be determined by linear sweep voltammetry with a glassy carbon electrode. The oxidation mechanism changes around 0.15 M H₂O₂. Catalytic decomposition was found to be much smaller at glassy carbon electrodes than at platinum electrodes. An almost linear calibration curve was obtained up to 60 mM H₂O₂. Interferences from Cu²⁺, Zn²⁺, Ni²⁺, Al³⁺, Fe³⁺ and Pb²⁺ as well as from the stabilizers were small. All measurements were made in sulphuric acid solutions.     

1,3,4-Trisubstituted-2-azetidinone Derivatives as Novel Receptors for Bismuth(III) Ion-Selective Electrodes: Application in Pharmaceutical and Glass Samples

Abstract

Polymeric membrane electrodes (PMEs) and coated graphite electrodes (CGEs) containing 1,3,4-trisubstituted-2-azetidinone derivatives as ion carriers are reported here for bismuth(III) ion selectivity. These electrodes exhibited Nernstian response for Bi³⁺ ions over a wide concentration range (5.0 × 10^?7 M to 1.0 × 10^?1 M for CGE) with a lower detection limit of 3.98 × 10^?7 M (for CGE) and wide pH range (1.3–5.0). Compared to polymeric membrane electrode, the coated graphite electrode has shown better selectivity for Bi³⁺ ions with respect to common metal ions. Proposed electrodes have been used for the estimation of Bi³⁺ ions in pharmaceutical and glass samples.     

Electrocatalytic Reduction of Oxygen at Anthraquinonedisulfonate/Polypyrrole Composite Film Modified Electrodes and Its Application to the Electrochemical Oxidation of Azo Dye

We report here the electrocatalytic reduction of oxygen on thin anthraquindisulfonate (AQDS)/poplypyrrole (PPy) composite film modified electrodes and its application to the electrooxidation of azo dye‐amaranth. The polymer‐coated cathode exhibited good electrocatalytic activity towards oxygen reduction reaction (ORR), and allowed the formation of strong oxidant hydroxyl radical (^.OH) in the medium via Electro‐Fenton's reaction between cathodically generated H₂O₂ and added or regenerated Fe²⁺. The electrochemical behaviors of ORR in various pH solutions were described using cyclic voltammetry (CV), rotating disk electrode (RDE) and chronoamperometric (CA) techniques. The effect of solution pH on amaranth mineralization by the Fe²⁺/H₂O₂ and Fe³⁺/H₂O₂ electrooxidation systems was studied. In addition, the long‐term electrocatalytic activity and stability of the AQDS/PPy composite film during multiple experimental runs were also examined electrochemically.     

A copper ion-selective electrode with high selectivity prepared by sol-gel and coated wire techniques

A sol-gel electrode and a coated wire ion-selective poly(vinyl chloride) membrane, based on thiosemicarbazone as a neutral carrier, were successfully developed for the detection of Cu (II) in aqueous solutions. The sol-gel electrode and coated electrode exhibited linear response with Nernstian slopes of 29.2 and 28.1 mV per decade respectively, within the copper ion concentration ranges 1.0×10^–5–1.0×10^–1 M and 6.0×10^–6–1.0×10^–1 M for coated and sol-gel sensors. The coated and sol-gel electrodes show detection limits of 3.0×10^–6 and 6.0×10^–6 M respectively. The electrodes exhibited good selectivities for a number of alkali, alkaline earth, transition and heavy metal ions. The proposed electrodes have response times ranging from 10–50 s to achieve a 95% steady potential for Cu²⁺ concentration. The electrodes are suitable for use in aqueous solutions over a wide pH range (4–7.5). Applications of these electrodes for the determination of copper in real samples, and as an indicator electrode for potentiometric titration of Cu²⁺ ion using EDTA, are reported. The lifetimes of the electrodes were tested over a period of six months to investigate their stability. No significant change in the performance of the sol-gel electrode was observed over this period, but after two months the coated wire copper-selective electrode exhibited a gradual decrease in the slope. The selectivity of the sol-gel electrode was found to be better than that of the coated wire copper-selective electrode. Based on these results, a novel sol-gel copper-selective electrode is proposed for the determination of copper, and applied to real sample assays.     

Determination of Hg on poly(vinylferrocenium) (PVF)-modified platinum electrode

A new surface based on poly(vinylferrocenium) (PVF⁺)-modified platinum electrode was developed for determination of Hg²⁺ ions in aqueous solutions. The polymer was electrodeposited on platinum electrode by constant potential electrolysis as PVF⁺ClO₄⁻. Cl⁻ ions were then attached to the polymer matrix by anion exchange and the modified electrode was dipped into Hg²⁺ solution. Hg²⁺ was preconcentrated at the polymer matrix by adsorption and also complexation reaction with Cl⁻. Detection of Hg²⁺ was carried out by differential pulse anodic stripping voltammetry (DPASV) after reduction of Hg²⁺. Mercury ions as low as 5 × 10⁻¹⁰ M could be detected with the prepared electrode and the relative standard deviation was calculated as 6.35% at 1 × 10⁻⁶ M concentration (n = 6). Interferences of Ag⁺, Pb²⁺ and Fe³⁺ ions were also studied at two different concentration ratios with respect to Hg²⁺. The developed electrode was applied to the determination of Hg²⁺ in water samples.     

Potentiometric Study of Coated Graphite Electrode and Polymeric Membrane Electrode for the Determination of Sm3+ Ion

Preliminary studies on the two Schiff bases N2‐((3H‐indol‐3‐yl)methylene)‐6‐phenyl‐1,3,5‐triazine‐2,4‐diamine (L₁) and N2,N4‐bis((3H‐indol‐3‐yl)methylene)‐6‐phenyl‐1,3,5‐triazine‐2,4‐diamine (L₂) have shown that they can act as Sm³⁺ selective electrodes. The performances of a polymeric membrane electrode and a coated graphite electrode based on L₂ were compared and the CGE proved to be better, as it shows a low detection limit of 1.8×10^?8 mol L^?1, a Nernstian slope of 19.6±0.4 mV decade^?1 of activity with a response time of 11 s in the pH range of 3.0–9.0. The CGE was used to determine Sm³⁺ in medicinal plants and soil samples. It was also used to determine fluoride ions in mouthwash samples and in toothpaste.     

Advanced oxidation processes for decolorization of aqueous solution containing acid red G azo dye

Some investigations concerning the decolorization of Acid Red G azo dye by photooxidation with hydrogen peroxide were performed. The influences of pH, oxidant concentration, and the presence of Fe²⁺ or other metal ions (Co²⁺, Cu²⁺, Ni²⁺, Mn²⁺) as potential catalysts, were investigated. The best results were obtained in the presence of ferrous ions in acid and neutral media. The other ions are not as effective as Fe²⁺ for dye decolorization. Co²⁺ and Cu²⁺ ions have a catalytic action, at low concentration, within a wide range of pH. Ni²⁺ and Mn²⁺ ions have no catalytic effect in photooxidation with hydrogen peroxide at acid Ni²⁺ and Mn²⁺ ions have no catalytic effect in photooxidation with hydrogen peroxide at acid pH values, but show a weak action in alkaline media.     

Electrochemical Properties of Hydroxyphenazine-Coated Electrodes

Glassy carbon and gold electrodes were coated with 1-hydroxyphenazine, and the electrochemical properties of these electrodes were tested using them as a rotating disc electrode to reduce Ru (bipy)₃³⁺, Fe³⁺, quinoxaline, O₂, and to oxidize Eu²⁺. The fixed redox couple can be reversibly reduced and oxidized, and acts as an intermediate medium for the electron transfer. For example the Ru(bipy)₃³⁺ (E_1/2= 1010 mV vs. SCE. (saturated calomel electrode) on a glassy carbon electrode in 1M H₂SO₄) is only reduced at 50 mV, whereas the oxidation of Eu²⁺ (E_1/2= ?460 mV vs. SCE. on a Hg-electrode in 1M HCl) takes place at ? 100 mV. The heterogeneous rate constant depends on the second order reaction between the attached coating and the redox couple in solution. Depending on this rate constant, selectivity of the electrode is observed.     

Ex Situ Scanning Electrochemical Microscopy (SECM) Investigation of Bismuth‐ and Bismuth/Lead Alloy Film‐Modified Gold Electrodes in Alkaline Medium

Scanning electrochemical microscopy (SECM) in feedback mode was employed to characterise the reactivity and microscopic peculiarities of bismuth and bismuth/lead alloys plated onto gold disk substrates in 0.1 mol L^?1 NaOH solutions. Methyl viologen was used as redox mediator, while a platinum microelectrode was employed as the SECM tip. The metal films were electrodeposited ex situ from NaOH solutions containing either bismuth ions only or both bismuth and lead ions. Approach curves and SECM images indicated that the metal films were conductive and locally reactive with oxygen to provide Bi³⁺ and Pb²⁺ ions. The occurrence of the latter chemical reactions was verified by local anodic stripping voltammetry (ASV) at the substrate solution interface by using a mercury‐coated platinum SECM tip. The latter types of measurements allowed also verifying that lead was not uniformly distributed onto the bismuth film electrode substrate. These findings were confirmed by scanning electron microscopy images. The surface heterogeneity produced during the metal deposition process, however, did not affect the analytical performance of the bismuth coated gold electrode in anodic stripping voltammetry for the determination of lead in alkaline media, even in aerated aqueous solutions. Under the latter conditions, stripping peak currents proportional to lead concentration with a satisfactory reproducibility (within 5 % RSD) were obtained.     

A Polyaniline-Deposited Nonplatinum Metal as a Potentiometric Sensor—An Inexpensive Alternate to Conventional Platinum for Some Potentiometric Redox Reactions

For the purpose of employing an inexpensive alternative to conventional platinum for use by upper-division as well as graduate students, polyaniline (PANI)-deposited stainless steel (SS) and mild steel (MS) electrodes are described as indicator electrodes for potentiometry and potentiometric titrations of some redox reactions. PANI is deposited on the nonplatinum metal by electrochemical polymerization of aniline using cyclic voltammetric technique. Alternate methods to produce the PANI electrodes are also suggested. The electrodes respond to concentration changes of hydroquinone (H₂O), Fe²⁺/Fe³⁺, and [Fe(CN)₆]^4–/[Fe(CN)₆]^3– in HCL electrolytes, and the potential variation with concentration follows the Nernst relationship. Under identical experimental conditions, the response time of the PANI/SS, PANI/MS, and Pt electrodes for a change in concentration of Fe³⁺ in a mixed electrolyte of Fe²⁺ and Fe³⁺ is found to be about 20 s. Neutralization reaction of HC1 versus NaOH, redox reaction of Fe²⁺ and Ce⁴⁺, and redox reaction of Fe²⁺ and KMnO₄ in several concentrations in the range from 1 mM to 100 mM are carried out using the PANI/SS, PANI/MS, and Pt indicator electrodes. The performance of the PANI/SS and PANI/MS electrodes is as good as that of the Pt at all concentration levels of the titrations. The electrodes can be reused for several titrations by storing them in an acid electrolyte for a long period of time. Thus, the conventional inert Pt or Au can be substituted for by using a PANI-deposited nonplatinum reactive metal as a potentiometric sensor for redox titrations.     

Characterization and Optimization of Interdigitated Ultramicroelectrode Arrays as Electrochemical Biosensor Transducers

Interdigitated ultramicroelectrode arrays (IDUAs) were fabricated on glass wafers and investigated to obtain optimal oxidation and reduction reactions of potassium ferro/ferrihexacyanide, Fe^2+/3+(CN)₆, when using a 2‐electrode set up. These electrodes will be used as transducers in portable microfluidic‐based biosensors in the future for the detection in an aqueous, biocompatible matrix. IDUAs were designed to maximize the signal‐to‐noise ratio (S/N) investigating electrode height, gap size, finger width, and material. Interesting differences in the electrode materials gold and platinum were found, which were due to the oxidization of platinum and gold during the IDUA fabrication process. It resulted in gold IDUAs being by far superior in respect to signal‐to‐noise ratio and overall signal magnitude to those made of platinum. The effects of gap size, electrode width and number of electrode fingers were as expected. Optimal electrode heights were in the range of 70 nm–140 nm, much larger and smaller electrodes had lower signal‐to‐noise ratios due to overall reduced signal or increased background. The optimized IDUA was made out of gold, had 400 fingers with a finger width of 2.7 μm, a finger height between 70 nm and 140 nm and a gap size of 0.9–1 μm. A detection limit of as low as 0.1 μM ferro/ferrihexacyanide measured in a simple 2‐electrode set up was obtained with a signal‐to‐noise ratio of 9.7.     

A Prussian blue-based reactive electrode (reactrode) for the determination of thallium ions

A reactive electrode (reactrode) made of Prussian blue (PB), graphite and paraffin can be used for a selective determination of thallium ions down to a concentration of 2 · 10^–8 mol 1^–1. The working principle of the reactrode is that thallium ions can be pumped into Prussian blue during alternating oxidation-reduction cycles. After a preconcentration of thallium ions in PB, the voltammetric determination follows as usually in anodic stripping voltammetry, i.e. the thallium ions are reduced to thallium metal which is subsequently oxidized to give the anodic stripping signal. The peculiarity of the Prussian blue-thallium system is that the thallium ions are situated in the holes of the PB matrix. When reduced to metallic thallium, they are substituted by potassium ions. Cd²⁺, Fe³⁺, Zn²⁺, Cu²⁺ and Ni²⁺ do not interfere up to a hundredfold excess, NH₄⁺ does not interfere up to a thousandfold – and Bi³⁺ up to tenfold excess. The interference by Pb²⁺ can be suppressed with EDTA.     

Selective Determination of Zn2+ Ion in Various Environmental,Biological and Medicinal Plant Samples Using a Novel Coated Graphite Electrode

Novel Zn²⁺ ion‐selective PVC based coated graphite electrodes were fabricated using the ionophores N‐((1H‐indol‐3‐yl)methylene)thiazol‐2‐amine (I₁), N‐((1H‐indol‐3‐yl)methyl)‐thiazol‐2‐amine (I₂) and 1‐((1H‐indol‐3‐yl)methylene)urea (I₃). Their potentiometric performance was examined in dependence of the addition of plasticizers and anion excluders and compared. It is found that the coated graphite electrode with the composition I₁:KTpClPB:o‐NPOE:PVC=9 : 1.5 : 51 : 38.5 is the best with respect to the wide working concentration range (4.2×10^?8–1.0×10^?1 mol L^?1), low detection limit (1.6×10^?8 mol L^?1) and wide pH range of 3.0–8.0. The proposed electrode was successfully applied to quantify Zn²⁺ in various environmental, biological and medicinal plant samples and used as indicator electrode.     

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.     

Response mechanism of platinum electrode to uncoupled ions(I)

The transient response mechanism of the platinum electrode to the uncoupled ions may be interpreted with the mixed phase formation (MPF) model of the transient response of precipitate-based ion-selective electrodes to interfering ions for K_xy ≪ 1. It is discovered that the peak height of the transient signal is related to the solubility of M(OH)₂ and hydration heat of M²⁺. The relation between the positive peak height of transient signal of pb²⁺ or cd²⁺ and lga_m obey the Nernst equation, while that of Ca²⁺ or Mg²⁺ does not. The equilibrium potential is not of Nernst response for all ions. Project supported by the National Natural Science Foundation of China.