bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal and photochemical control of an electrochemical process at an isomerizable spiropyran monolayer‐modified Au electrode
Authors: Katz Eugenii , Willner Itamar
Published: May 2005

An isomerizable monolayer‐modified electrode is used to control interfacial electron transfer by means of external signals. A spiropyran (SP) monolayer undergoes thermal isomerization to the positively charged merocyanine monolayer, MRH+, while the latter isomer monolayer is photoisomerized, λ > 475 nm, to the SP‐monolayer state. Pyrroloquinolino quinone (PQQ) is used as redox component for probing the interfacial electron transfer. The MRH+‐monolayer electrode attracts the negatively charged PQQ and effective electron transfer is attained. Upon photochemical isomerization to the SP‐monolayer electrode, the interfacial electron transfer is inhibited. Reversible activation and deactivation of the interfacial electron transfer is accomplished by cyclic isomerization of the monolayer through the MRH+ and SP‐states, respectively, using thermal and photochemical signals.
Study of the nickel‐based chemically modified electrode obtained by electrochemical deposition of an NiII‐tetramethyl‐dibenzo‐tetraaza [14] annulene complex. Redox catalysis of carbohydrates in alkaline solutions. II
Authors: Cataldi Tommaso R. I. , Desimoni Elio , Ricciardi Giampaolo , Lelj Francesco
Published: May 2005

The electrochemical treatment of an electropolymerized (NiIIL)n thin film (where L represents 5,7,12,14‐tetramethyl‐dibenzo[b,i]‐1,4,8,11‐tetraaza [14] annulene) gives rise to a nickel‐based catalytic deposit on conducting substrates [glassy carbon (GC), platinum, or gold electrodes], which shows strong similarities to the nickel hydroxide electrode. The effect of potential cycling on surface composition, chemical status, and morphology of this nickel‐based chemically modified electrode (Ni‐CME) has been investigated by cyclic voltammetry (CV) [1], X‐ray photoelectron spectroscopy (XPS), and scanning electron microscopy. XPS analysis was very useful for characterizing the chemical changes in the nickel coordination caused by electrochemical treatments in alkaline solution. The featureless surface of the as‐prepared GC/(NiII)Ln, film compared with the fractal nature of the GC/Ni‐CME was revealed by electron micrographs. The Ni‐ CME exhibits high electrocatalytic activity towards the oxidation of carbohydrates in alkaline solution. The electrooxidation capability of the Ni‐CME is highlighted by the amperometric detection of sugars after anion‐exchange liquid chromatographic separations with alkaline mobile phases.
Lipid‐modified pyrolytic graphite electrodes for the study of negatively charged species
Authors: Bianco Pierre , Haladjian Jean
Published: May 2005

Pyrolytic graphite (PG) electrodes are coated with films of dodecylamine (DDA), dimethyldioctadecylammonium bromide (DODAB) or composite layers based on a mixture of phosphatidylcholine (PC) and cholesterol (CH). Cyclic voltammetry is used to investigate the incorporation of two negatively charged species, Fe(CN) and spinach ferredoxin, into the DDA or DODAB layers, as a function of time and composition of the cast films. No signal corresponding to the spinach ferredoxin redox reaction is detected at the PG electrode simply coated with a mixed (PC‐CH) layer. Well‐shaped responses denoting redox reaction of ferredoxin are observed when the (PC‐CH) layer is doped with DDA (or DODAB). The results support the electrostatic nature of the interactions between negatively charged species and the positive charges in the lipid layer.

Such coated electrodes seem well‐suited for studying negatively charged species. They provide a good model for mimicking physiological redox protein‐membrane interactions.
Adsorptive stripping voltammetric determination of ultratrace concentrations of molybdenum in biological and environmental materials on a glassy carbon mercury film electrode
Authors: Adeloju Samuel B. O. , Pablo Fleurdelis
Published: May 2005

The determination of ultratrace concentrations of molybdenum(VI) by adsorptive cathodic stripping voltammetry on a glassy carbon mercury film electrode is described. The method involves a controlled preconcentration of the element by interfacial accumulation as molybdenum‐8‐hydroxyquinoline (oxine) complex on the electrode followed by a cathodic stripping voltammetric measurement. The optimum analytical conditions for the measurement of molybdenum by this method include the use of 0.20 M acetate buffer at pH 5.25, 1 mM oxine, an accumulation potential of −0.40V (vs. Ag/AgCl) and a rotated electrode at 3000 rpm. Under these conditions, the linear concentration range and lowest detectable concentration obtained with a 5‐min accumulation were 0–300 μg L−1 (R2 = 0.997) and 0.5 μg L−1 [relative standard deviation (RSD) = 13.7%], respectively. The presence of most other metal ions do not interfere with the molybdenum determination, except for PbII and CdII which were successfully masked by addition of 3 μM EDTA, and TiIV and WVI which were masked by 1 μM tartaric acid. The interference of surface‐active substances, such as Triton X‐100, is overcome by UV irradiation of the sample. The use of the adsorptive stripping voltammetric technique, after decomposition by dry ashing and UV treatment, is successfully demonstrated for the determination of molybdenum in biological and environmental materials.
Ion‐sensitive field‐effect transistors and ion‐selective electrodes as sensors in dynamic systems
Authors: Izquierdo Andrés , de Castro María D. Luque
Published: May 2005

The state‐of‐the‐art of both ion‐sensitive field‐effect transistors (ISFETs) and ion‐selective electrodes (ISEs) when working in continuous flow systems is reviewed. The features and development of each type of sensor are established, and the advantages of the use of one or the other are discussed.
Kinetic study of electrocatalytic reduction of hydrogen peroxide at iron(III) porphyrin modified glassy carbon electrode in alkaline medium using the rotation‐scan method
Authors: Dong Shaojun , Liu Baifeng , Liu Junli , Tabard Alain , Guilard Roger
Published: May 2005

Reduction of hydrogen peroxide at a glassy carbon (GC) electrode modified with σ‐bonded pyrrole iron(III) octaethylporphyrin complex, (OEP)Fe(Pyr), was studied by cyclic voltammetry and a rotating disk electrode. In 0.1 N NaOH solution, it is shown that such an (OEP)Fe(Pyr)/GC electrode has a significant catalytic activity towards hydrogen peroxide reduction (ED = −0.80 V, k = 0.066 cm s−1); however, the electrode stability is low. The deactivation is observed when the reaction charge (Q) is passing through the (OEP)Fe(Pyr)/GC disk electrode. A linear rotation scan method is applied to study the kinetic process by determining the disk electrochemical response (iD) to rotation rate (ω) at a definite disk potential (ED). Considering that the number of adsorbed electroreduced catalyst molecules (Red) varies according to the disk potential, a factor θ (= ΓRed/(ΓRed + ΓOx)) is introduced to describe the electrode surface area fraction for electroreduced species. The obtained Koutecky–Levich equation is applicable whatever the potential is.
Voltammetric and photoelectron spectral elucidation of the electrocatalytic oxidation of hydrogen peroxide at screen‐printed carbon electrodes chemically modified with cobalt phthalocyanine
Authors: Gilmartin Markas A. T. , Ewen Richard J. , Hart John P. , Honeybourne Colin L.
Published: May 2005

The interplaying mechanisms involved in the electrocatalytic oxidation of hydrogen peroxide (H2O2) have been studied using cyclic and differential‐pulse voltammetry and X‐ray photoelectron spectroscopy (XPS). Cobalt phthalocyanine (CoPC) modified screen‐printed carbon electrodes (SPCEs) were used as base transducers in the voltammetric studies, and for XPS experiments a mixture of the printing ink containing CoPC was coated onto a steel stub. These investigations have shown that CoPC is initially in the Co2+ oxidation state, and that in plain supporting electrolytes it is subsequently electrochemically oxidized to Co3+. A postulated sequence of events for the mediated oxidation of H2O2 at CoPC‐SPCEs has been derived from the XPS and voltammetric data generated.
Carbon paste electrode incorporated with cobalt(II) octaethoxyphthalocyanine for the amperometric detection of hydrogen peroxide
Authors: Mizutani Fumio , Yabuki Soichi , Iijima Seiichiro
Published: May 2005

A hydrogen peroxide sensing electrode was prepared by incorporating cobalt(II) octaethoxyphthalocyanine [CoPc(OEt)8] into a carbon paste (CP) matrix. The CoPc(OEt)8‐modified electrode could oxidize hydrogen peroxide at lower potentials than a CP electrode with unsubstituted cobalt phthalocyanine (CoPc). In addition, the CoPc(OEt)8‐based system showed a high stability; the electrode response to 10mM hydrogen peroxide did not decrease for over 6 h, whereas the hydrogen peroxide response from the CoPc‐modified electrode reduced to half the initial value within 2 h. The CoPc(OEt)8, which is a paraffin oil soluble derivative of CoPc, incorporated into the bulk of the CP diffused towards the electrode surface so as to renew the electrode surface, and this resulted in the high stability of the CoPc(OEt)8‐modified electrode. The electrode was used as the transducer for an L‐lactate‐sensing enzyme sensor; the sensor could be used for more than 4 weeks and 400 assays.
Nitrite‐selective electrode based on an electropolymerized cobalt phthalocyanine
Authors: Allen John R. , Florido Antonio , Young Shelley D. , Daunert Sylvia , Bachas Leonidas G.
Published: May 2005

Cobalt(II) 4,4′,4″,4″′‐tetraaminophthalocyanine was electropolymerized on glassy carbon by cyclic voltammetry. The formed polymeric films were shown to interact selectively with anions and were used in the design of ion‐selective electrodes. Different polymerization conditions, as well as different conditioning solutions and buffer systems, were investigated in order to optimize the response of the electrodes. The electrodes were found to be most selective for nitrite. The slopes of the calibration plots were sub‐Nernstian and the detection limit for nitrite was 1.7 × 10−4 M.
Highly sensitive biosensing of phenolic compounds using bioaccumulation/chronoamperometry at a tyrosinase electrode
Authors: Wung Joseph , Chen Qiung
Published: May 2005

Biocatalytic accumulation is used to greatly enhance the sensitivity of tyrosinase enzyme electrodes for phenolic compounds. By allowing the enzymatic reaction to proceed for different time periods (under open‐circuit conditions) it is possible to accumulate the quinone product near the transducer surface. The subsequent chronoamperometric response is substantially higher than analogous bioassays without accumulation. For example, with 3 min accumulation, a 28‐fold signal amplification is observed. Assays of microliter (40 μL) samples are reported, yielding a detection limit of 2 × 10−8M (88 pg) catechoi following a 3 min accumulation. The influence of various experimental variables is explored. Applicability to bioassay of relevant environmental samples is illustrated.
Pulse polarography study of the complexes of lead with azacrown [2,2,2]cryptand in the presence of an excess of competing sodium ion
Authors: Cukrowski Ignacy , Marsicano Fabrizio , Hancock Robert D. , Cukrowska Ewa
Published: May 2005

Differential pulse polarography (DPP) has been used to determine the formation constants of PbII at ionic strength 0.5 M and 25 °C with [2, 2, 2]cryptand in the presence of 0.5 M sodium nitrate. The equilibrium between Pb2+ and the ligand is established slowly on the polarographic time scale, so that two well‐separated peaks are observed, that for the metal ion and for a nonlabile ML complex for which the stability constant was found to be log K1 = 12.9. The equilibrium between the ML complex and hydroxide ion appeared to be fast and a substantial shift in the peak potential of the ML complex was observed. Two labile lead complexes are reported, namely ML(OH) and ML(OH)2 for which stability constants (log β) were found to be 20.51 and 23.75, respectively. The Lingane equation has been modified to allow calculation of formation constants for labile complexes of lead with two ligands, [2, 2, 2]cryptand and OH−. A single, second, overall protonation constant of [2, 2, 2]cryptand at an ionic strength of 0.5 M and 25°C in the presence of 0.5 M Na+ is reported and its value was found to be log β2 = 18.
Electrochemical oxidation of DNA at a gold microelectrode
Authors: Pang Dai‐Wen , Qi Yi‐Peng , Wang Zong‐Li , Cheng Jie‐Ke , Wang Jia‐Wang
Published: May 2005

The electrochemical oxidation of DNA at a gold microelectrode has been investigated using cyclic voltammetry with a homemade microliter cell. Denatured DNA is adsorbed and oxidized more easily at the gold electrode than native DNA. The electrochemical oxidation of DNA also depends on its strand length. The DNA oxidation product adsorbs strongly on the gold electrode, so poisoning and inactivating its surface; the adsorbed product also inhibits electrooxidation of the gold surface.
Electrochemical behavior of NbV–EDTA and NbV–citrate systems in aqueous solutions
Authors: Gomes Maria Das Graças , Franco Douglas W.
Published: May 2005

The electrochemical reduction of NbV using oxalatoniobic acid and ammonium oxooxalatoniobate salts was studied in aqueous solutions of citric acid and sodium ethylenediaminetetraacetate (EDTA), in a wide range of supporting electrolyte concentrations and pH. In EDTA two reduction processes were observed: NbV to NbIV, E = −1.000 V vs. Ag/AgCl at pH 4.50 and NbIV to NbIIIE = −1.400 V vs. Ag/AgCl (pH 4.50). In citric acid there was only one reduction process: (NbV to NbIV), E = −1.260 V vs. Ag/AgCl at pH 4.50. In both electrolytes a linear relationship was found between the diffusion current and the niobium concentration in the 1.0 × 10−5 to 5.0 × 10−3 M range. Using cyclic voltammetry, it waa observed that the charge transfer process in the NbV to NbIV process is reversible in EDTA and reversible–quasireversible in citric acid.
Reminiscences of Professor Wilhelm Simon and his research work at the ETH Zürich
Authors: Morf Werner E. , Pretsch Ernö
Published: May 2005

The Symposium on Electrochemical Sensors was dedicated to the memory of the late Professor Wilhelm Simon. We all remember him as a remarkable and renowned scientist, and as an enthusiastic and inspiring lecturer. In particular, he was a pioneer in research on ion‐selective electrodes. With this article, the authors would like to pay due reverence to him and to his outstanding contributions to analytical chemistry.
Studies on the phase boundaries and the significance of ionic sites of liquid membrane ion‐selective electrodes
Authors: Bühlmann Philippe , Yajima Setsuko , Tohda Koji , Umezawa Kayoko , Nishizawa Seiichi , Umezawa Yoshio
Published: May 2005

Attenuated total reflectance infrared spectroscopy (ATR‐IR) has been used to study the cation permselectivity of liquid‐membrane ion‐selective electrodes (ISEs). All spectroscopic evidence was found to agree with the interpretation of permselectivity as being due to complete exclusion of counter‐ions from the boundary phase. Compared to ATR‐IR, optical second harmonic generation (SHG) has an even more pronounced surface sensitivity. It has been demonstrated to be a promising new technique for the study of ISE response mechanisms, as it allows one to observe the actual phase boundary. On the other hand, further potentiometric evidence for the influence of ionic sites on the emf response was found, both by a study of membranes free of ionic sites as well as by the investigation of leaching processes at poly(viny1 chloride) membranes. Finally, the use of a photoresponsive crown ether ionophore allowed the determination of emf response characteristics in relation to the ionophore concentration without any changes in the membrane composition.
Computer modeling of the membrane–solution interface of liquid membrane ion‐selective electrodes
Authors: Vincze Arpad , Horvai George , Leermakers Frans A. M.
Published: May 2005

The potentiometric behavior of liquid membrane ion‐selective electrodes with neutral carrier has been qualitatively reproduced by a computer model. Phenomena like Nernstian response, cation and anion interference, detection limit and the effect of lipophilic salt additives could be successfully modeled.
Some recent studies on the use of electrochemical sensors in nonaqueous solution chemistry
Authors: Izutsu Kosuke , Nakamura Toshio , Arai Tomoko , Ohmaki Masayuki
Published: May 2005

Four recent studies in the authors' laboratory on the use of electrochemical sensors in nonaqueous solutions are reported. (1) Si3N4‐ and Ta2O5‐type ISFETs proved to be useful in nonaqueous solutions as sensors for pH and for proton solvation, because of their more rapid response than a conventional glass electrode. They were used to study the acid–base equilibria in γ‐butyrolactone and to determine the proton transfer activity coefficients between different solvents. (2) A univalent cation‐sensitive glass electrode was used to study the solvation of lithium ions in mixed solvents applicable to lithium batteries. (3) A membrane of polyacrylamide coupled to a cobalt phthalocyanine complex and coated onto a platinum electrode functioned as a sensor for fluoride and cyanide ions in aprotic solvents. It was used to determine the solubility products of alkali and alkaline earth metal fluorides and cyanides in acetonitrile and propylene carbonate. (4) A new method is proposed for the estimation of the liquid junction potential between different solvents, and a comparative study has been made between the new method and some conventional methods.
A solid composite pH sensor based on quinhydrone
Authors: Düssel Heike , Komorsky‐Lovrić Šebojka , Scholz Fritz
Published: May 2005

A solid composite pH sensor can be made from quinhydrone, solid paraffin and surface‐modified graphite powder. It exhibits an almost theoretical slope of the potential–pH dependence (−57.7 mV at 25°C), a formal potential E0′ = 0.6922V (vs. NHE), low standard deviations for repeated measurements (0.04 pH units), fast potential response (15s) and a working range up to pH 9.5. The sensor can be used in moderately concentrated mineral acids and, unlike the conventional quinhydrone electrode, it is also applicable for measurements in milk. The sensor shows the same salt effect and sensitivity towards strong oxidants and reductants as the conventional quinhydrone electrode. The surface modified graphite was prepared by boiling graphite powder with concentrated nitric acid. By voltammetry it was shown that the surface of the modified graphite contains surface‐confined redox centers similar to those in quinhydrone, which can catalyze the electron transfer of the quinhydrone on the surface of the sensor.
Characterization of modified electrodes by electrochemical quartz crystal microbalance, radiotracer technique and impedance spectroscopy
Authors: Inzelt György
Published: May 2005

The significance and reliability of the data determined by different in‐situ methods (electrochemical quartz crystal microbalance, radiotracer and impedance spectroscopy) on the film formation and redox transformations of polymers are discussed. Results on both redox and conducting polymer films are selected in order to illustrate the practical and theoretical problems of the field.
Potentiometric oxygen sensing with copper films: Response mechanism and analytical implications
Authors: Meruva Ravi K. , Meyerhoff Mark E.
Published: May 2005

The electrochemical response mechanism of a previously reported potentiometric oxygen (O2) sensing system based on thin films of copper sputtered on single crystal Si(100) is examined. The potentiometric O2 response of such films is shown to depend on sample stirring rate as well as the pH, ionic strength and nature of the buffer salts within the test solution. XPS studies of the copper films exposed to solution for several days confirm the presence of compper corrosion products on the surface. These findings, in conjunction with cyclic voltammetric measurements, suggest that the potentiometric O2 response originates from slow corrosion of copper and simultaneous reduction of O2 at the surface of the thin films. A steady‐state situation exists when the rates of these two reactions are equal, resulting in a corrosion potential (also referred as rest potential Er for the system) that varies in a near Nernstian (1 e−) manner with the partial pressure of O2 in solution. A mathematical formulation for this type of response, based on the Butler–Volmer equation, is presented. The analytical implications of these findings with respect to devising useful potentiometric O2 sensors based on copper films are discussed.
The effect of a nonadsorbing electroactive species on the transition time in derivative adsorptive chronopotentiometric stripting analysis
Authors: Honeychurch Michael J. , Ridd Michael J.
Published: May 2005

A theory to describe the enhancement of the transition time and change in peak shape for the chronopotentiometric reduction of an adsorbed species caused by the reduction of an electroactive diffusing species is presented. The equations were derived for planar, cylindrical and spherical electrodes and verified for the chronopotentiometric reduction of adsorbed cystine, as mercurous cysteine thiolate, on a hanging mercury drop electrode in the presence of dissolved oxygen.
Solid‐state hydrogen sensor based on a solid‐polymer electrolyte
Authors: Samec Zdeněk , Opekar František , Crijns Guido J. E. F.
Published: May 2005

An electrochemical hydrogen sensor has been constructed, based on two platinum electrodes that differ in their true‐to‐geometrical surface area ratios and that are in contact with Nafion. The electrodes attain different mixed potential values in air containing hydrogen and thus the sensor does not require a reference atmosphere (pure air). The potential difference between the electrodes can be used for potentiometric or amperometric detection of hydrogen. The detection sensitivity strongly depends on the relative humidity (RH) of the test air. Within a hydrogen concentration range from 40 to 4000ppm (v/v) and with RH varying between 33 and 95%, the sensitivity of potentiometric detection decreases with increasing RH from 149 to 113 mV per concentration decade, while that for amperometric detection increases from 0.67 to 1.25 nA/ppm. On a step change in the hydrogen concentration, a value of 95% of stationary response is attained within ca. 140 s for potentiometric detection and ca. 50s for amperometric measurement.
Study on electrocatalytic oxidation of NADH by ferrocene derivatives and determination of catalytic rate constant at microdisk electrode
Authors: Tian Min , Dong Shaojun
Published: May 2005

The electrocatalytic oxidation of NADH by ferrocene derivatives and the influence of complexation with β‐cyclodextrin (β‐CD) were investigated at a microdisk electrode in a buffer solution. The cyclic voltammetric behavior of the ferrocene derivatives on the microdisk electrode was used to determine the electron‐transfer rate constant from NADH to the ferricinium species. The heterogeneous rate constants and the diffusion coefficient of ferrocene derivatives were determined with the microdisk electrode. The effect of temperature and pH on the electrocatalytic oxidation of NADH were assessed.
Ion‐exchange voltammetry at polymer‐coated electrodes: Principles and analytical prospects
Authors: Ugo Paolo , Moretto Ligia M.
Published: May 2005

This review describes principles and analytical applications of ion‐exchange voltammetry (IEV) at polymer modified electrodes. Results of mechanistic studies which are relevant to the development and optimization of IEV methods are discussed. Useful examples of IEV determinations of traces of inorganic and organic electroactive ions of interest for environmental, biomedical or pharmaceutical analysis are given along with future prospects for this technique.
On‐line amperometric assay of glucose, L‐glutamate, and acetylcholine using microdialysis probes and immobilized enzyme reactors
Authors: Yao Toshio , Suzuki Seita , Nishino Hirohito , Nakahara Taketoshi
Published: May 2005

A highly selective on‐line, real‐time monitoring system is proposed for amperometric assay of glucose, L‐glutamate, and acetylcholine. The system includes a microdialysis probe, immobilized enzyme reactor, and poly(1,2‐diaminobenzene)‐coated platinum electrode. The analyte in the dialysate from the microdialysis probe is enzymatically converted to produce hydrogen peroxide. The hydrogen peroxide is detected selectively at a poly(l,2‐diaminobenzene)‐coated platinum electrode, without any interference from oxidizable species and proteins. The present method can be successfully applied to in vitro assay of glucose and in vivo monitoring of glucose in rat brains. However, the sensitivity is not sufficient for in vivo monitoring of trace amounts of L‐glutamate and acetylcholine in rat brains.
A portable flow injection analyzer for use with ion‐selective electrodes
Authors: Dimitrakopoulos Telis , Alexander Peter W. , Hibbert D. Brynn , Cherkson Len , Morgan John
Published: May 2005

A battery powered portable monitor based on flow injection potentiometry has been developed weighing 1.8 kg, constructed in a carry‐case and applicable for remote site monitoring. Portability has been achieved using a light weight rechargeable Ni‐Cd battery‐pack (7.2 V). The flow injection manifold incorporates a low powered peristaltic pump, a wall‐jet type flow cell containing a commercial iodide ion‐selective electrode and a Ag/AgCl reference electrode connected to an analog‐to‐digital converter, also powered by the battery pack, and a RS232‐serial output to a notebook computer for real‐time data display and storage. The system performance has been evaluated using the iodide ion‐selective electrode, including the effects of various carrier solutions on sample peak heights, peak widths and the calibration slopes and working ranges. Fast response with peak widths as low as approximately 10 s. was observed with near Nernstian response of −53.8 mV change per activity decade and a log‐linear range between 5 × 10−6 and 1 × 10−2M in a 0.1 M sodium acetate carrier stream.
Electrochemical reduction of o‐nitrophenol as a tool for the rough characterization of organic matter in seawater samples
Authors: Gas̆parović Blaz̆enka , Ćosović Božena
Published: May 2005

Phase sensitive alternating current (AC) voltammetry with o‐nitrophenol (ONP) as a probe is used as a simple nondestructive method for a rough characterization of organic substances in natural seawater samples. This is based on the measurement of the effects of adsorbed organic substances on the peak height and the potential of the ONP reduction peak. In this work further improvements are presented of the method which is achieved by introducing the measurement of the prepeak of ONP reduction obtained upon scan reversal. The height of the prepeak is extremely sensitive to the type of organic matter adsorbed on the mercury electrode at the pH of natural seawater. The ONP prepeak increases in the presence of adsorbed layers of negatively charged organic substances, such as humic and fulvic acids and proteins. In the presence of adsorbed polysaccharides of dextran type there is no increase of the ONP prepeak height. With increasing concentrations of the polysaccharides a small decrease of the prepeak is observed. The application of the method is demonstrated on different seawater samples from the north Adriatic sea.
Voltammetric behavior of pyrimethamine in veterinary formulations using square‐wave and adsorptive square‐wave techniques
Authors: Berzas J. J. , Rodríguez Juana , Lemus J. M. , Castañeda G.
Published: May 2005

The voltammetric behavior of pyrimethamine (PMT) was studied by square‐wave (SW) and square‐wave stripping (SWS) techniques, leading to two methods for its determination [in presence of sulfaquinoxaline (SQX)] in aqueous samples and veterinary formulations. Due to overlapping response of SQX and PMT the first derivative was used for the simultaneous determination of these two components. The relative standard deviations obtained for concentration levels of PMT as low as 3 × 10−6 M (SW) and 5 × 10−7 M (SWS) were 2.2% and 2.7% (n = 10), respectively.
The electrochemical behavior of methylene blue at a microcylinder carbon fiber electrode
Authors: Ju Huangxian , Zhou Jun , Cai Chenxin , Chen Hongyuan
Published: May 2005

The electrochemical behavior of methylene blue (MB) at a carbon fiber microcylinder electrode, was studied by cyclic voltammetry. The charge transfer coefficient α of the electrode reaction with two‐electron transfer is 0.5, and the number of H+ participating in the electrode process is 3 at pH 2.2–5.4, 2 at pH 5.4–6.0 and 1 at pH 6.0–10.7, respectively. The standard electron transfer rate constant ko′, and standard formal potential Eo′ of MB at various pH were determined by using the carbon fiber microcylinder electrode. The electrode reaction mechanism of methylene blue at various pH is proposed. The adsorbability of MB at the electrode is discussed and explored by cyclic voltammetry and chronocoulometric technique.
Behavior of cathodically pretreated platinum on Fe(CN) electroreduction in KNO3: Dependence on pretreatment
Authors: Pillai K. Chandrasekara , Thangamuthu Rangasamy , Ilangovan Govindasamy
Published: May 2005

Platinum electrode, cathodically pretreated by polarizing it in the hydrogen evolution region, has been studied in detail for its electrode activity towards Fe(CN) electroreduction in 1 M KNO3. HClO4 acid has been used to cathodically pretreat the Pt electrode in order to avoid specific adsorption effect of anions, so that the intrinsic electrochemical activity of cathodically pretreated Pt electrode is assessed. Similar studies have been carried out with anodically pretreated and heat treated electrodes. Cyclic voltammetry (CV) and rotating disk electrode techniques (RDE) have been used to evaluate kinetic parameters and the results indicate that the adsorbed H‐adatoms on Pt surface retard Fe (CN) reduction by two orders. This has been explained in terms of a double layer effect and enhanced adsorption of the impurities by adsorbed H‐adatoms on the surface. Effect of potential cycling as a pretreatment method has also been examined.
From polarography of DNA to microanalysis with nucleic acid‐modified electrodes
Authors: Paleček Emil
Published: May 2005

Nucleic acids are electroactive species producing well developed voltammetric peaks on the mercury electrode sensitively reflecting small damages to the double‐helical DNA. Nucleic acid‐modified electrodes can easily be prepared by immersing the electrode into a 5 μL drop of the DNA and/or RNA solution. Such nucleic acid‐modified electrodes strongly decrease the quantities of DNA and RNA required for analysis. They offer a number of other advantages which may be of use in biochemical and molecular biological research. Past, present and future aspects of nucleic acid voltammetric analysis are reviewed.
Electrochecmical biosensors for DNA sequence detection
Authors: Mikkelsen Susan R.
Published: May 2005

A review of reported biosensors for the sequence‐selective detection of analyte DNA sequences shows that signal transduction based on electrogenerated chemiluminescence, potentiometry and voltammetry are all capable of detecting analyte DNA at attomole levels. In contrast, optical and piezoelectric transducers detect DNA at picomole and femtomole levels, respectively. The principles and applications of these promising electrochemical DNA biosensors are described and discussed.
Studies of electroreduction of nitropentane and nitrohexane on mercury electrodes in the presence of adsorbed aliphatic alcohols
Authors: Xuan Hai Trinh , Maksymiuk Krzysztof , Stroka Jadwiga , Galus Zbigniew
Published: May 2005

Electroreduction of 1‐nitropentane and 1‐nitrohexane was studied on mercury electrodes in aqueous solutions, together with the inhibitors: n‐pentanol, n‐hexanol and n‐heptanol. The electrode behavior of these species was not found to be influenced by inhibitors at concentrations lower than 10 mM and 2 mM for n‐pentanol and n‐hexanol, respectively, because adsorption of nitrocompounds is stronger than that of alcohols. For high alcohol concentrations, when a total surface coverage by inhibitor molecules is almost achieved, the reaction of nitroalkanes is inhibited. Steric factors evaluated using the dependence of rate constant on inhibitor concentration were used in the determination of the orientation of reactant molecule on the electrode. For alcohol concentrations near saturation, the rate constant becomes independent of inhibitor concentration. In this case a reaction of nitroalkanes dissolved in the surface organic phase was postulated.
Cathodic stripping voltammetry of D‐penicillamine and N‐acetylcysteine in the presence of nickel ion
Authors: Ion Ana , Bǎnicǎ Florinel G. , Fogg Arnold G. , Kozlowski Henryk
Published: May 2005

D‐Penicillamine (Pen) can be preconcentrated on a hanging mercury drop electrode in the presence of NiII (0.5 mM) at potentials between 0.0 and −0.4V vs. Ag/AgCl, (3 M KCl). Pen is adsorbed either as the mercury thiolate or as the NiII Pen complex. Accumulation as the nickel complex occurs at the more negative potentials in this range, i.e., near −0.4V, where mercury thiolate is not formed. When the mercury thiolate has been accumulated and mercury ion is reduced during the scan, Pen is released to form the nickel(II) complex. This overall accumulation behavior is typical of thiol compounds that form strong chelate complexes with NiII.

Pen in the adsorbed state catalyzes the reduction of NiII giving a differential pulse cathodic stripping voltammetric peak at −0.6V (pH 7). Pen can be determined at concentrations down to 15 nM. N‐Acetylcysteine (Ac‐CysH) which has no catalytic properties for the reduction of NiII, can be determined at pH 7 in phosphate‐acetate buffer, using the reduction peak of its accumulated mercury thiolate salt. The mutual interferences of Pen and Ac‐CysH are negligible.
An electrochemical and spectrophotometric study of some charge‐transfer complexes involving drug molecules in acetonitrile
Authors: Ball Rowena V. , Eckert George M. , Gutmann Felix , Wong Danny K. Y.
Published: May 2005

The electron donating properties of the drugs, amiodarone, desethylamiodarone, promethazine and codeine have been studied using the electrochemical technique of conductivity titration, complemented by electronic absorption spectroscopy. All were found to form charge transfer complexes in vitro with the electron acceptor iodine in acetonitrile. A quantitative explanation has been proposed to account for the observed temperature dependence of the conductivity. This is based on consideration of the opposing effects of charge mobility and the temperature‐dependent donor‐acceptor equilibrium. An assessment of the use of the hydrochloride form, instead of free base, of drugs in examining the model systems for the study of drug donor‐acceptor interactions is also presented.
Method for determination of gold in solutions with high oxidation/reduction potential
Authors: Viltchinskaia Elena A. , Zeigman Lev L.
Published: May 2005

This article proposes a method for detecting the concentration of gold ions in solutions with high oxidation/reduction potential (ORP), such as aqua regia, a hypochlorite‐iodine mixture, and a new proprietary liquid bromine carrier solution, by direct current anodic stripping voltammetry (DCASV). The working electrode is a graphite electrode impregnated with a mixture of epoxy resin and polyethylene amine. The article discusses: possible cause of a double stripping peak for gold appearing in voltammograms in aqua regia solution with electrolysis potentials less than −0.4 V; differences in coefficients of the working electrode's sensitivity in the above mentioned solutions. A relative standard deviation of the results in determining gold concentration in solutions of rock (ORP > 0.9 V), which were obtained by the proposed method and by atomic‐absorption spectrophotometry, did not exceed 0.2.
Scanning tunneling microscopy characterization of electrode materials in electrochemistry
Authors: Li Jing , Wang Erkang
Published: May 2005

Ex situ and in situ STM characterization of the electrode materials, including HOPG, GC, Au, Pt and other electrodes, is briefly surveyed and critically evaluated. The relationship between the electrode activity and surface microtopography is discussed.
Preparation and characterization of Ag‐intercalated copper hexacyanoferrate films on electrodes
Authors: Malik Marcin A. , Kulesza Pawel J.
Published: May 2005

We demonstrate the possibility of preparation of a mixed metal hexacyanoferrate system, silver‐containing copper hexacyanoferrate, in the form of a thin film on glassy carbon electrode substrate. This novel microstructure is characterized using conventional cyclic voltammetry, visible absorption spectrophotometry, as well as solid‐state electrochemistry in the absence of contact with liquid electrolyte. The results imply distinct physicochemical identity of the system in comparison to silver‐free copper hexacyanoferrate. Incorporation of Ag influences the selectivity of counter‐cation transport which supports redox reactions of the modified electrode in alkali metal supporting electrolytes. Thus the Ag‐intercalated material may be considered for ion‐exchange applications. Following in situ electroanalytical determinations, based on coulometry and stripping‐like voltammetry, we postulate stoichiometries, AgICuIIFeIII(CN)6 and KAgICuIIFeIII(CN)6, for the oxidized and reduced structures.
A model for a redox species confined to a thin layer with a variable diffusion coefficient
Authors: Cassidy John , McCormac Timothy
Published: May 2005

A numerical simulation has been carried out for a redox couple confined to a thin layer under potential step or cyclic voltammetric conditions where the diffusion coefficient is determined by the relative amounts of the oxidized form (of diffusion coefficient D1)and reduced form (of diffusion coefficient D2). An overall layer diffusion coefficient D is determined by the mole fractions of species 1 and 2; D(n1 +n2)=n1D1 +n2D2. This layer diffusion coefficient is proposed as an alternative model to that of interaction parameters used to characterize nonidealities during potential step and cyclic voltammetric experiments of surface confined redox species.
Applications of self‐assembled monolayers in electroanalytical chemistry
Authors: Mandler Daniel , Turyan Iva
Published: May 2005

The different approaches in which self‐assembled monolayers (SAMs) have been applied in electroanalytical chemistry are reviewed. Three principal concepts have been used and can be categorized according to the mechanism of attachment of the monolayer to the electrode. These include the formation of covalent bonds between reactive organic molecules, such as chlorosilanes, with activated surfaces, the formation of lipid and bilayer lipid membranes that self‐assemble on conductive surfaces and the adsorption of functionalized alkanes, e.g., alkanethiols, on well ordered surfaces. Systems for detecting inorganic, organic and biological species are described and conclusions are drawn.
Alternating current investigations at the mercury drop electrode on the adsorption potential of metal complexes
Authors: Sander Sylvia , Henze Günter
Published: May 2005

In adsorptive stripping voltammetry (AdSV) the analyte is accumulated on the electrode surface in the form of a metal complex and the determination step is carried out voltammetrically. Usually the technique is sensitive to the effects of other absorbable organic substances. Alternating‐current (AC) investigations on the complexes of uranium, vanadium and antimony with chloranilic acid, uranium with cupferron and cobalt and nickel with dimethylglyoxime gave information about their adsorption behavior on the electrode surface. Furthermore the AC voltammetric behavior of the nonionic surfactant Triton X100 was shown. By knowing the adsorption potential and range of adsorption, predictions about the effects of organic adsorbates can be made. Importantly the optimal accumulation potential of the complex for its AdSV‐determination may be obtained. With appropriate potential control the selective accumulation of the analyte complex can be achieved and so avoid the influence of these other adsorbates in favorable cases.
Pencil‐Leads as new electrodes for abrasive stripping voltammetry
Authors: Blum Doris , Leyffer Wolfgang , Holze Rudolf
Published: May 2005

A simplified procedure for abrasive stripping voltammetry involving a standard potentiostat, a function generator and common graphitic materials is described.
The catalytic polarographic prewave of nickel(II) induced by 2‐methylbenzimidazole
Authors: Calzón Josefa García , Ordieres Arturo J. Miranda , Alvarez Jesús L. MuňÍz , Fonseca Juan M. López
Published: May 2005

A comprehensive study of the prewave of NiII induced by 2‐methylbenzimidazole in sodium barbital/nitric acid/potassium sulfate media was carried out by using various polarographic techniques in order to establish the mechanism via which the underlying electrode reaction proceeds. Based in the proposed mechanism, the formation of the catalytic complexes is a surface process involving deprotonated 2‐methylbenzimidazole; the adsorption of this compound over the catalyst concentration where the prewaves are well‐defined conforms to a Langmuir isotherm. Accordingly, a plot of the reciprocal of the limiting current for the prewave against the reciprocal of the ligand‐catalyst concentration is a straight line. This finding was exploited for the determination of 2‐methylbenzimidazole at concentrations from 5 × 10−7 to 5 × 10−5 M from NiII prepeaks recorded by differential pulse polarography and square‐wave voltammetry.
Studies of the preparation and analytical application of polypyrrole‐coated microelectrodes for determination of aluminum
Authors: Barisci Joseph N. , Murray Peta , Small Chris J. , Wallace Gordon G.
Published: May 2005

Methods that enable the preparation of cation sensitive polymer‐coated microelectrodes have been developed. The analytical utility of these electrodes has been demonstrated with the detection of aluminum in flowing solutions. Detection limits in the low ppb range have been obtained. The response for several potentially interfering cations was evaluated.
Selectivity of hybrid voltammetric determinations
Authors: Lubuda JÁN , Vaníčková Mária
Published: May 2005

The selectivity of solvent extraction voltammetry and ion‐exchange voltammetry hybrid procedures has been investigated. The equations for the prediction of the selectivity value according to the extraction constants or distribution coefficients of the analyte and interfering component were obtained. Their verification and application at the determination of trace metals in model and real samples are presented.
Anodic stripping voltammetry of tungsten at graphite electrodes
Authors: Malakhova Natalia A. , Popkova Galina N. , Wittmann Gertrud , Kalnichevskaia Liubov N. , Brainina Khjena Z.
Published: May 2005

Trace levels of tungsten can be determined at a graphite electrode using anodic stripping voltammetry. Tungsten is concentrated at the electrode surface after reduction to Wv as a insoluble ternary complex in the presence of rhodanide ions and antipyrine (ANT) or 4‐ dimethyl‐aminoantipyrine (pyramidon, PYR). The optimal conditions of this determination are: electrolyte 1 M H2SO4 containing 0.078 M NH4SCN + 0.04M ANT or 0.02M PYR; deposition potential −0.50 V; sweep from −0.4 to −0.05 V using differential pulse stripping technique. Detection limit is 1 × 10−9M (0.2 μg/L) for a 180 s accumulation time (with a relative standard deviation of 15%). Results obtained for waste waters, steel and olive leaves are reported.
Resolution of differential potentiometric stripping analysis
Authors: Garai Tibor , Nagy Zoltan , Mészáros Lajos , Bartalits Liliana , Locatelli Clinio , Fagioli Francesco
Published: May 2005

The resolution of differential potentiometric stripping analysis has been evaluated in terms of the difference in the half‐wave potentials, the number of electrons involved in the electrode reactions and the concentration ratio of the ions to be determined simultaneously. The asymmetry of the dt/dE vs. E function was found to affect the resolution considerably. In other words the interference is considerably enhanced when the half‐wave potential of the interfering ion is more cathodic than that of the measured one while in the reverse case the resolution is much improved.
Preconcentration by flow reversal in conductometric sequential injection analysis of ammonium
Authors: Oms M. T. , Cerdà A. , Cerdà Victor
Published: May 2005

A simple sequential injection method for the determination of ammonium with conductometric detection is described. The sample and alkaline solution are sequentially aspirated into a single tubular channel and mixed by flow reversal. The formed ammonia permeates through a gas permeable membrane and is collected on a static acceptor solution. The change in conductance of the acceptor solution is related to the concentration of ammonium ions in the sample. The use of flow reversal and influence of sample residence time on preconcentration are studied. The detection limit can be lowered from 1.5mg L−1 to 0.1 mg L−1 if preconcentration by successive sample flow reversal is used. The relative standard deviation is lower than 3%.
A photo‐cured calcium ion‐selective electrode for use in flow injection potentiometry that tolerates high perchlorate levels
Authors: Dimitrakopoulos Telis , Farrell John R. , Iles Peter J.
Published: May 2005

An improved photo‐cured membrane selective to calcium was developed based on the calcium bis[4‐(l, 1,3,3‐tetramethylbutyl)phenyl] phosphate ionophore and incorporates the lipophilic additive, potassium tetrakis(p‐chloropheny1)borate. The calcium electrode exhibited a hyper‐Nernstian response of 31.0 mV change per activity decade and a log‐linear range between 1 × 10−5 to 0.1 M in pure calcium chloride solution, in steady‐state mode. The calcium electrode was fast responding, reaching 90% of steady‐state value in 5s making it ideal for flow injection measurements. The photo‐cured electrode can measure calcium in a high perchlorate background, and was used to determine the total calcium level in full cream milk that was digested by a nitric/perchloric acid mixture. The results obtained were in good agreement with atomic absorption spectroscopy measurements.
Parameters in the design of oxygen detecting oxidase enzyme electrodes
Authors: Gooding J. Justin , Hall Elizabeth A. H.
Published: May 2005

The response of an amperometric oxidase enzyme electrode, monitored by the consumption of oxygen, was numerically modeled using a two substrate model. The reduction current was found to be sensitive to the thiele modulus, Φ, which is dependent on the square of the biorecognition matrix thickness and the concentration of active enzyme within this matrix. The detectable concentration range to which the sensor can be used can be extended by reducing the membrane thickness or the enzyme loading, both of which reduce the signal change with substrate additions. The dependence of Φ on the square of the membrane thickness makes the sensor design exceedingly sensitive to minor changes in thickness and hence manufacturing of reproducible sensors with common deposition methods exceedingly difficult.