bluuebunny/crossref_metadata_2025 huggingface dataset:
Simultaneous measurement of plasma serotonin, catecholamines, and their metabolites by an in vitro microdialysis‐microbore hplc and a dual amperometric detector
Authors: Cheng Fu‐Chou , Lin Nai‐Nu , Kuo Jon‐Son , Cheng Lee‐Ju , Chang Fang‐Mai , Chia Lie‐Gan
Published: May 2005

Many advantages of a method for the simultaneous measurement of plasma norepinephrine (NE), epinephrine (E), dopamine (DA), 3,4‐dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), serotonin, and 5‐hydroxyindole‐3‐acetic acid by the in vitro microdialysis‐microbore high‐performance liquid chromatography‐electrochemical detection (MD‐MHPLC‐ED) technique have been described in our previous article. The present experiment uses a dual electrode electrochemical detector (DUED) in the MD‐MHPLC system, providing an additional reliable measurement or assignment of peaks by identifying the peaks based on their redox ratios at the oxidation/reduction cycle. Thus, the important early eluting front and interfering peaks were eliminated on the cathodic chromatogram. Within 15 minutes, an isocratic separation of these analytes is achieved by using microbore column. Hence, theoretically, over 90 analyses can be performed in a single working day. The detection limit (S/N = 3) of this method was about 0.2 to 0.5 pg per injection. The required volume of plasma samples is less than 200 μL. Thus, blood loss is minimal with repeated blood sampling, especially in experiments using small animals. This simple, efficient, and sensitive method can, therefore, be used as a basic research tool in the investigation of blood biogenic amines and their metabolites.
A polarographic investigation on interactions between cu(ii) ions and natural degradation products of a herbicide atrazine
Authors: Grabec Irena , Ogorevc Božidar , Hudnik Vida
Published: May 2005

A study was performed to investigate the possible formation of coordination compounds between Cu(II), Cd(II), Zn(II), and Pb(II) ions and natural degradation products of atrazine (ATR) desisopropylatrazine (DIA), desethylatrazine (DEA), and desethyldesisopropylatrazine (DEIA), as well as parent compound ATR itself and the related s‐triazine herbicide prometryne (PRO). By using polarographic and voltammetric titrations of a metal ion with a ligand and vice versa, at mercury drop or plain carbon paste electrode, only a formation of coordination compounds involving Cu(II) ions, of a type CuL2 (L = DEA, DIA, and PRO) and CuL (L = DEIA) in aqueous solutions at pHs above 4, were observed. By applying an indirect polarographic method with ligand exchange (EDTA), a conditional stability constant of CuDEIA was determined, and the value β CcuDEIA = 12.7 was obtainted.
Condensation α‐cyclodextrin polymer membrane with covalently immobilized glucose oxidase and molecularly included mediator for amperometric glucose biosensor
Authors: Kutner Wlodzimierz , Wu Huihuang , Kadish Karl M.
Published: May 2005

A highly permeable film of the condensation α‐cyclodextrin polymer (α‐CDP) was used as a membrane for fabricating a “second‐generation” glucose amperometric biosensor. Glucose oxidase (GOD) was covalently immobilized, whereas 1,4‐benzoquinone (BQ), or tetrathiafulvalene (TTF) mediator molecules were included in the membrane by the α‐cyclodextrin sites. A simple one‐step procedure for the biosensor preparation was developed. It consisted of casting the membrane onto the surface of a glassy carbon, gold, or platinum disk substrate from an aqueous solution, pH 2.0 (HCl), containing equimolar quantities of a water‐soluble α‐cyclodextrin prepolymer, a glutaric dialdehyde cross‐linking reactant, GOD, and the mediator. Cyclic voltammetry (CV) limiting currents for glucose biocatalytic electrooxidation were measured for different enzyme loadings and mediator dosings inside the membrane as well as for different glucose conoentrations in a (0.1 M phosphate buffer + 0.1 M NaClO4) pH 7.0 solution. The limiting‐electrocatalytic currents at the (α‐CDP)‐GOD‐TTF electrode were pH independent and occurred atE1/2= 0.03 V (vs. SCE), i.e., at a favorably low potential value. The detectability of glucose was 10 μM for the (α‐CDP)‐GOD‐BQ electrode at the 2 mg (18.5 unit) GOD loading and a signal‐to‐noise ratio of 3. The values of apparent Michaelis constant for glucose and the maximum limiting electrocatalytic current density, determined from the Michaelis‐Menten analysis for the 1 mg (18.5 unit) GOD loading, were (4.5 ± 0.5) mM and (190 ± 20) μA cm−2for the (α‐CDP)‐GOD‐BQ electrode, and (5.6 ± 0.8) mM and (137 ± 16) μA cm−2for the (α‐CDP) GOD‐TTF electrode, respectively. The sensor performance was examined with respect to the method of membrane preparation, membrane composition, and long‐term stability. Miniaturization of the biosensor is facile if, for instance, a 10 μm Pt disk microelectrode substrate is used.
Evaluation of a new solid‐state reference electrode junction material for ion‐selective electrodes
Authors: Diamond Dermot , McEnroe Eamonn , McCarrick Mary , Lewenstam Andrzej
Published: May 2005

The performance and properties of a new low‐resistance material, Refex, suitable for use in reference electrode junctions is described. The material is a solid polyvinyl acetate that contains a very‐ large loading of KCl (1:1 w/w KCI/PVA). Despite relatively large active surface areas in the designs studied (stand‐alone reference and combination pH), leakage rates of KCl are remarkably low. pH measurements in ultrapure water and comparative measurements in common buffer solutions against standard reference electrodes confirm the stability of the potential developed across the junction to be very stable. Impedance studies verify the importance of the KCl doping for realization of the low resistance and attractive electrochemical properties of the material.
Determination of aluminum ions by indirect potentiometry in a flow system
Authors: Ngila J. Catherine , Alexander Peter W. , Hibbert D. Brynn
Published: May 2005

A potentiometric system is described for the indirect flow determination of Al3+ with an aluminum wire as indicator electrode. The method is based on the reaction between aluminum and fluoride ions at pH 5.0 in acetate buffer. The reduction in activity of fluoride ions is detected by the aluminum electrode. The response was optimized for the flow rate of solution, length of reaction tubing, concentration of fluoride reagent, and pH of the buffer. The response was linear with concentration of aluminum in the range of 0.5 to 50 ppm with a relative standard deviation (RSD) of 0.7%. There was negligible interference from a range of cations and anions when their concentrations were less than 20 ppm.
Determination of CD, CU, and PB in animal tissues—comparison of electrochemical results obtained with a new polarographic system and atomic spectroscopy
Authors: Šestáková Ivana , Miholová Daniela , Slámová Alžběta , Mader Pavel , Száková Jiřina
Published: May 2005

Reference materials of animal origin have been analyzed for Cd, Cu, and Pb contents by voltammetry using ECO‐TRIBO Polarograph with pentype renewed Hg electrode after dry ashing in superoxidizing atmosphere (mixture of O3 + O2 + NOx). The contents of all metals mentioned were independently determined in aliquots of identical digests by atomic absorption spectrometry (AAS). Statistical evaluation showed good correlation between both methods. Moreover, dectrochemical results the obtained for biological certified reference material (CRM) 12‐02‐01 Bovine Liver are in very good agreement with certified values for Cd and Pb.
On the electrochemical oxidation of 5‐hydroxy barbituric acid
Authors: Berchmans Sheela , Vijayavalli R.
Published: May 2005

The electrochemical behavior of 5‐hydroxy barbituric acid (HB) has been investigated in aqueous and nonaqueous media. In aqueous medium, there is only one anodic peak at –50 mV (at v = 20 mV/s), and no cathodic peak is observed indicating an irreversible reaction under the conditions of this study. The cyclic voltammograms indicate a two‐electron transfer reaction corresponding to the oxidation of HB to alloxan monohydrate (AM). In nonaqueous medium, voltammetric response is observed both in the anodic as well as the cathodic directions. The anodic peak occurs at +140 mV and the cathodic peak occurs at –320 mV at v = 20 mV/s. At high scan rates (v > 200 mV/s) there are two cathodic peaks. The mechanism of oxidation of HB is discussed, and the rate constants of the reaction are calculated.
Characterization of a wall‐jet electrode/flow‐injection analysis system
Authors: Huang Yu Liang , Khoo Soo Beng , Yap Miranda G. S.
Published: May 2005

A “wall‐jet” electrode (WJE) was studied as an electrochemical deteaor for flow‐injection analysis (FIA). Mathematical expressions were obtained for the peak current responses of the electrode, both for an uncoiled open tubular conduit and also in the presence of a packed‐bed reactor between the injection valve and detector. The derived relationships between peak current and volumetric flow rate, and injected sample volume and concentration of the analyte were verified by using the ferricyanide ion and hydrogen peroxide as test samples. In general, theory and experiment were in good agreement although a discrepancy in the volumetric flow rate dependence of the peak current was observed in the presence of a packed‐bed reactor.
Determination of epinine in human urine by high‐performance liquid chromatography coupled with electrochemical detection using carbon fiber microelectrodes
Authors: Hua Chi , Lee Hian Kee , Hsieh An Kong
Published: May 2005

Epinine was detected with a simple and disposable carbon fiber flow electrode after being separated by high‐performance liquid chromatography (HPLC). An alumina adsorption procedure was used for the extraction of epinine from urine samples. The extraction recoveries at 1, 3, and 6 μg/mL epinine concentration levels were 66.9 ± 3.7, 65.6 ± 3.3, and 67.0 ± 3.4%, respectively (n = 5). Linear responses to epinine in urine were obtained over the range of 0 to 10 μg/mL. The detection limit (signal‐to‐noise ratio = 5/1) for epinine in urine was 15 ng/mL.
Differential pulse polarography of some organic peroxides
Authors: Salvato B. , Jambon C. , Vittori O. , Rochefort O.
Published: May 2005

Severan organic peroxides were studied by differential pulse polarography (DPP) in water and water–solvent media, and compared to hydrogen peroxide. Reduction occurred usually between −0.1 and +0.3 V vs. SCE, except for the peroxides containing a tert‐butyl group adjacent to the OO function. In this case, reduction was more difficult and was shifted to the −0.9 to −1.1 V vs. SCE range. Diffusion coefficients were determined and are in the 4 − 9 × 10−10 m2 s−1 range. The detection limits are generally no lower than 5 × 10−5 mol l−1, due to the high irreversibility of the reduction process. Calibration plots from 5 × 10−5 to about 5 × 10−4 mol l−1 exhibit very good linearity.
Amperometric detection of the ammonium ion by facilitated ion transfer across the interface between two immiscible electrolyte solutions
Authors: Osborne Murray D. , Girault Hubert H.
Published: May 2005

Facilitated ion transfer reactions of the ammonium, potassium, and sodium ions with the ionophores dibenzo‐18‐crown‐6, nonactin, and valinomycin were investigated at the water/ 1, 2‐dichloroethane interface. Association constants for the various reactions studied were calculated to determine the selectivity imparted by the ionophores on the transferring ions. Of the ionophores studied, nonactin was found to be the most selective towards the ammonium ion, with a calculated association constant of 14.1.
Flow injection potentiometric determination of harmine and harmaline hallucinogens
Authors: Hassan Saad S. M. , Elnemma Eman M. , Hamada Marawan A.
Published: May 2005

Flow injection analysis (FIA) systems incorporating potentiometric sensors for harmine and harmaline hallucinogens are described. The sensors are based on the use of harmine and harmaline tetraphenylborate or reineckate as electroactive compounds dispersed in plasticized PVC matrix. Laboratory‐build flow‐through sandwich cell equipped with silver disk coated with the sensing material is used as a detector in a low dispersion FIA system. The detector exhibits fast and linear response over the concentration range 10−2−10−6 M harmine or harmaline with a detection limit of 2 μg/mL (for 100 μL samples). Operational pH ranges from 3 to 8, sampling rate is 80 per hour and the precision is typically ±0.6%. Recovery and reproducibility data agree fairly well with those obtained by gas–liquid chromatography.
Stable layers of oxyethylated iso‐octylphenols adsorbed on the surface of a hanging mercury drop electrode under tensammetric conditions
Authors: Pawlak Maria Krystyna
Published: May 2005

The stability of films of oxyethylated alkylphenols of the Triton X series on the hanging mercury drop electrode was investigated. The stability of the adsorbed layers increases upon increasing the concentration of the substance. More stable films were obtained after saturation of the electrode surface with monomeric forms. The stability of the film increases in the presence of associated forms.
Electroactive coatings of dicyano‐bis(1,10‐phenanthroline)iron(II) attached to Nafion polymer film modified electrodes via adsorption
Authors: Li Huimei , Li Yijun , Li Jinghong , Wang Erkang , Dong Shaojun
Published: May 2005

A dicyano‐bis(1,10‐phenanthroline)iron(II)/Nafion modified elecrode was prepared. The voltammetric and the spectroelectrochemical behavior of this electrode were investigated. The influence of pH and the amount of Nafion and dicyano‐bis(1,10‐phenanthroline)iron(II) (DBPI) used in the electrode preparation on the electrochemical behavior is presented.
Study of the adsorptive voltammetric behavior of the RhIII–5–Br–PADAP complex
Authors: Wang Chunming , Hong Chunlin , Li Hulin
Published: May 2005

The adsorptive voltammetric behavior of the RhIII–2–(5–bromo–2–pyridylazo)–5–diethylaminophenol (5–Br–PADAP) complex was studied with the linear scan technique in a solution of 0.01 mol/L NaOAc‐0.07mol/L HOAc–35% ethanol (supporting electrolyte, pH 4.2).A very sensitive and selective adsorptive stripping voltammetric method for the determination of Rh is described. The proposed method can be used for determining trace rhodium in the concentration range 7.8 × 10−9–9.7 × 10 −7 mol/L without interference from other noble metal ions. At the same time, a simple oscillopolarographic procedure for determining Rh in the same electrolyte is also proposed.
Investigating polymers and conducting metals as transduction mediators or immobilization matrices
Authors: Hall Elizabeth A. H. , Skinner Nigel G. , Jung Christoph , Szunerits Sabine
Published: May 2005

An equivalent circuit, which extends the Randles model to include coupled chemical steps, is considered for a finite diffusion layer, describing synthetic metals. Information was used, concerning the effect of interaction of solution species on the layer circuit, together with complimentary kinetic parameters from a nonlinear least squares fit to the dispersion data, of two‐dimensional model functions, to study the glucose induced response of polyaniline and NMP.TCNQ in glucose oxidase loaded synthetic metals.
Microfabrication technology of flexible membrane based sensors for in vivo applications
Authors: Buck Richard P. , Cosofret Vasile V. , Lindner Erno , Ufer Stefan , Mudaras Marcel B. , Johnson Timothy A. , Ash R. Bruce , Neumun Michael R.
Published: May 2005

Potentiometric ion‐sensitive planar microelectrode arrays, and amperornetric enzyme‐containing biosensors were fabricated by photolithographic microelectronic technology on a flexible polyimide substrate. The steps of the microelectronics processing are summarized in more detail than previously described. The ion‐selective electrodes were tested in blood serum, whole blood, and in the hamstring muscle of anesthetized rabbits. The test and performance characteristics of planar pH are emphasized, and K+, Na+, and Ca2+ data are included in this review. New applied results are presented from experiments where the electrodes have been implanted into an in situ porcine beating heart at the midmyocardial depth in order to monitor H+ and K+ changes during the course of coronary artery occlusion.
Amperometric phenol sensor with immobilized bacteria
Authors: Orupõld Kaja , Mashirin Aleksei , Tenno Toomas
Published: May 2005

An amperometric phenol sensor, wherePseudomonus putidabacteria were immobilized on an amperometric oxygen sensor is described. Theoretical considerations of the steady‐state concentration distribution of oxygen and substrate in diffusion‐controlled microbial sensors are given. Validation of the theory was evaluated by comparing the experimental and theoretical data.
Use of polymer films in amperometric biosensors
Authors: Emr Sally A. , Yacynych Alexander M.
Published: May 2005

Different types of polymeric films implemented in various capacities in amperometric biosensor design are reviewed. Conducting and nonconductinzg polymer films and composite films are considered. Methods of film fabrication such as solvent casting, electropolymerization, and adsorption are presented. Film function, including prevention of interference and fouling problems, immobilization of the enzyme or active biocomponent, extension of linear range, or to address biocompatibility problems are described. The use of polymeric films as a medium to incorporate mediators, while an important function, is too vast for review here. The applications of polymer film‐modified biosensors for selected analytical determinations are also presented. This review focuses upon the use of polymer films in amperometric biosensors and emphasizes innovative biosensor designs and unique applications, and omits traditional free‐standing films unless they are coupled with new types of polymer films or used innovatively.
Factors affecting the resistance and performance of fluoride ion‐selective electrodes
Authors: Shen Wei , Wang Xue D. , Cattrall Robert W. , Nyberg Graeme L. , Liesegang John
Published: May 2005

Some lanthanide fluoride (LnF3, Ln = Ce, Nd, Sm) crystals have been grown, and fluoride ion‐selective electrodes (F‐ISE) have been constructed using these and some commercial LaF3, single crystal membranes. Aspects of crystal growing, particularly the high‐temperature dimorphism of SmF3, are addressed, and the effects on the electrode resistance and response characteristics of crystal quality, doping and membrane geometric dimensions are studied. The results show that, while doping is effective in increasing the membrane conductivity, membrane geometric dimensions also affect the electrical resistance substantially. Undoped membranes have noise‐free Nernstian response to F− solutions, provided appropriate geometric dimensions are chosen. The crystal orientation of the membrane does not have noticeable effect on the performance. The crystal quality also affects the membrane resistance and performance. Single crystal membranes with minor and localized visual defects show little difference in conductivity and no difference in performance compared with a ‘perfect’ single crystal membrane. Membranes grown from lower grade starting materials do not show poorer performance although these membranes were slightly cloudy. Membranes with severe visual defects have much lower conductivity, and deteriorated performance.
Redox polymers for electrocatalytic oxidation of NADH – A random block methyl‐siloxane polymer containing meldola blue
Authors: Persson Björn , Lee Hung Sui , Gorton Lo , Skotheim Terje , Bartlett Philip
Published: May 2005

A water‐insoluble modified methyl‐siloxane polymer which held 9‐dimethylaminobenzo[a]phenoxazine‐7‐ium (Meldola Blue) units, was synthesized, characterized, and used to drop‐coat solid graphite electrodes. The electrocatalytic oxidation of the nicotinamide adenine dinucleotide (NADH) in the polymer could be described by the Michaelis–Menten type of kinetics as seen from steady‐state measurements in 0.25 M phosphate buffer, pH7, at 0 mV (vs. SCE). The electrocatalytic properties of the redox polymer was evaluated using the film thickness as a major variable. The theoretical model found to describe the NADH oxidation at the redox polymer modified electrode, is presented. A maximum NADH sensitivity of 40 μA cm−2 mM−1 at a coverage of 0.5 μg cm−2 was indicated.
Performance of platinum‐based spherical mercury microelectrodes in cyclic voltammetry and stripping analysis
Authors: Baldo M. Antonietta , Daniele Salvatore , Corbetta Massimo , Mazzocchin Gian A.
Published: May 2005

The performance of spherically shaped mercury microelectrodes, formed by electroreduction of mercury onto an inlaid platinum microdisk of radius r, characterized by different deposit heights, h, have been investigated for cyclic (CV) and anodic stripping (ASV) voltammetry. Electrodes with h/r ratio in the range 0.1–2 have been tested in solutions containing Pb2+ and Cd2+ in NaCl and NaClO4 + HClO4 as supporting electrolytes. For cyclic vodtammetry the results obtained indicated that the width at half height (w1/2), the peak current (ip) and the charge of the anodic stripping peak (Qs) depend on the h/r parameter. Particular attention has been devoted to the relation between the charge of the cathodic process and the anodic charge of the stripping peaks. It has been found that the experimental charge values involved in the cathodic and anodic scan agree within 3%, irrespective of the mercury thickness, indicating a complete stripping of the metals deposited in the mercury. For ASV the Pt‐Cd intermetallic compounds have been found to influence the stripping peak of cadmium for electrodes with h/r ≤ 1 and for concentrations of Cd2+ lower than 10−6 M. By exploiting the known properties of the mercury microelectrodes in stripping analysis, an absolute method, based on the charge associated with the stripping peak, has been applied for determining the labile fraction of the above cations in a pore‐water sample of the Venice lagoon.
A study of the hydroxide ion interference on several fluoride ion‐selective electrode membranes
Authors: Wang Xue D. , Shen Wei , Cattrall Robert W. , Nyberg Graeme L. , Liesegang John
Published: May 2005

A study of the response characteristics of some fluoride selective electrodes based on three lanthanide fluoride single crystal membranes (LnF3; Ln = La, Ce and Nd) is reported. There is little difference between the response of these three membranes in buffered fluoride solutions except that CeF3 shows a slightly faster response and a slightly lower detection limit. The effect of the hydroxide ion on the response to fluoride is examined and is shown to be particularly severe for the CeF3 membrane. It is demonstrated that hydroxide ion interference on these membranes is due to the formation of hydroxo‐complexes which form within a gel layer at the membrane surface. A mechanism is proposed for the response of the electrodes to the hydroxide ion.
Determination of nickel and cobalt in wastewaters and seawater by constant current stripping potentiometry with nitrite enhancement of the stripping signal
Authors: Nan Chen Guo , Cardwell Terence J. , Vincente‐Beckett Victoria A. , Hamilton Ian C. , Scollary Geoffrey R.
Published: May 2005

A rapid and highly sensitive method using constant current stripping potentiometry for the determination of nickel and cobalt in seawaters and industrial wastewaters has been established. The method is based on the adsorptive accumulation of nickel and cobalt in the presence of either dimethylglyoxime (DMG) or α‐benzyldioxime (α‐BD) prior to stripping using a constant reducing current. Nitrite is used in the stripping step for the catalytic enhancement of the stripping signal. Analytical protocols for standard solutions using DMG or α‐BD show good precision (RSD's between 3 and 4% on the same film) and detection limits (30 ng/L for Ni/DMG; 10‐ng/L for Co/DMG; 9ng/L for Co/α‐BD). However, iron interferes significantly with the determination of cobalt using α‐BD. With DMG, the simultaneous determination of nickel and cobalt is possible and has been developed into a protocol readily applicable to the routine determination of these metals. The analytical protocol is rapid, easy to perform and the results are in agreement with those obtained by graphite furnace atomic absorption spectrophotometry. The DMG procedure has also been optimized for the determination of cobalt alone, which has advantages for determinations at concentrations of 1 μg/L or less.
Redox kinetics in cathodic stripping square‐wave voltammetry
Authors: Lovrić Milivoj , Mlakar Marina
Published: May 2005

Several redox systems with reactants which are immobilized at the electrode surface (EuSal complex, SeIV and SeIV in the presence of CuII, cysteine and p‐nitrophenol) were studied by square‐wave voltammetry to examine whether their redox kinetics can be measured by using the phenomenon of the ‘quasireversible maximum’. This is explained in detail. The following standard rate constants are obtained: EuSal complex ks = 720 ± 31 s−1, SeIV/CuII, log [ks/(cms−1)] = 0.94 ± 0.9, cysteine, log [ks/(cms−1)] = 0.6 ± 0.9 and p‐nitrophenol, ks > 1200 ± 50 s−1.
Determination of mercury and silver at a modified carbon paste electrode containing glyoxal bis(2‐hydroxyanil)
Authors: Won Mi‐Sook , Moon Deog‐Whan , Shim Yoon‐Bo
Published: May 2005

Modified carbon paste electrodes(CPEs) for the analysis of mercury and silver have been constructed by incorporating a Schiff base, glyoxal bis(2‐hydroxyanil) (GHA) into the graphite powder and mixing with Nujol oil. Simple immersing of the GHA‐modified CPE into the measuring solution led to the chemical deposition of the metal ions onto the electrode. The cyclic, differential pulse, and stripping voltammetry were used to characterize the modified electrodes, which selectively responded to the mercury(II) and silver(I) ions. The analyses of Hg and Ag were carried out separately with the CPE in the acetate buffer and neutral aqueous solution. The electrode surface was regenerated after each measurement, by cycling the potential from more positive than that for the stripping of the reduced Hg to the more negative than that for the reduction of AgI ion. After seven deposition/measurement/regeneration cycles, the peak current of the analyte decreased. The response reproduced around 5% relative standard deviation using the differential pulse stripping voltammetry. The detection limits for HgII and AgI ions were 1.0 × 10−9 M and 1.0 × 10−10 M, respectively, for 40 min of deposition. After pretreatment of silver(I) ion with KCl, we could not observe any interference by other metal ions in the determination of the HgII ion in aqueous solution. Our results obtained in the determination of mercury are verified using a certified standard urine reference material, SRM's 2670 (trace elements in urine).
Electrooxidation of ascorbic acid on the dispersed platinum glassy carbon electrode and its amperometric determination in flow injection analysis
Authors: Casella Innocenzo G.
Published: May 2005

Cyclic voltammetry was used to investigate the electrochemical behavior of ascorbic acid at a platinum modified glassy carbon electrode (Pt‐CME) in perchloric acid solutions. Tafel slopes, reaction orders and pH effects were evaluated and a possible electrooxidation mechanism is reported.

Experiments in flow injection analysis were performed to characterize the electrode as an amperometric sensor for the determination of ascorbic acid. The effects of several common interferences on the amperometric signal were estimated.

The electrode stability, precision, limit of detection and linear range were evaluated at low and high potentials (i.e., 0.55V and 1.0 V). In particular, at 0.55V the limit of detection was 25 ng mL−1 and the calibration graph was linear in the range 60 ng mL−1350 μg mL−1 (correlation coefficient 0.999). The mechanism of the oxidation of ascorbic acid on the Pt‐CME is rather similar to the bulk platinum electrode, but in FIA a different behavior was observed. In particular, the Pt‐CME, after repetitive injections of ascorbic acid, shows very reproducible amperometric signals without recourse to pulsed waveform potentials. In contrast, bulk platinum electrodes shows a significant poisoning effect towards the electrooxidation of ascorbic acid, thus pulsed amperometric techniques are necessary to preserve the catalytic performance. Moreover, the Pt‐CME in comparison with the bulk platinum electrode, shows significant oxidation currents in the wide range of potentials (i.e., 0.4V–1.5 v).

Examples of the determination of ascorbic acid in fruit juice were achieved by flow injection analysis. Good levels of recovery (99–103%) were obtained. For comparison, the ascorbic acid was also determined in these samples by using a chromatographic method with UV detection at 254 nm.
Cadmium and lead complexation by anodic stripping voltammetry with a mercury microelectrode
Authors: Correia dos santos Margarida M. , Goņalves Maria L. Simões , Capelo Sofia
Published: May 2005

Complexation reactions of lead by glutamic acid in KNO3 0.1 M and cadmium by glycine at two ionic strengths (0.1 MKNO3 and 2 × 10−3 M borate buffer) have been used to : 1) compare the stripping response in DCASV (direct current anodic stripping voltammetry) and DPASV (differential pulse anodic stripping voltammetry) at large (hanging mercury drop electrode: HMDE) and small (thin film mercury microelectrode deposited on Pt/lr: μME) electrodes, 2) test classical DeFord‐Hume's method with microelectrodes coupled to DCASV and DPASV, and 3) analyze the suitability of both electrodes HMDE and μME coupled to anodic stripping voltammetry to measurements in freshwaters. Indeed due to the mass transport characteristics at microelectrodes, the fraction of a metal which contributes to the current may well be different from that at a conventional size electrode. The obtained results are in all the situations consistent among themselves and in good agreement with literature.
The voltammetric behavior of the plasmin‐modified carbon paste electrode in the presence of an electrogenic substrate
Authors: Longchamp Sylvie , Randriamahazaka Hyacinthe N. , Nigretto Jean‐Maxime
Published: May 2005

The catalytic properties of plasmin (Pln), irreversibly adsorbed on carbon paste electrodes are considered. The assay of the immobilized enzyme could be achieved with the availability of a specific and electrogenic substrate contained in the solution. The synthesis of this substrate, designated as S2644, was specially initiated for this purpose. The electrochemical properties of the electrode surface upon exposure to solutions containing the substrate or the products involved in the catalysis, or both, were examined by performing cyclic voltammetric measurements directly at the modified electrode. Results showed the dependence of the electrode potential conditions on the surface catalytic activities and the effect of the adsorbed species in the heterogeneous catalysis.
Electrochemical deposition of prussian blue films across interdigital array electrodes and their use in gas sensing
Authors: McCormac Timothy , Cassidy John , Cameron David
Published: May 2005

Prussian Blue films were deposited across carbon ink array electrodes and solid‐state voltammetry was performed. The current measured from the array, when the potential across the two electrode array was +0.5 V, was found to be dependent upon the nature of the bathing gas. It was seen that methanol, water vapor and dichloroethane lead to an increase in the measured current. Upon switching between nitrogen and the aforementioned gases the responses obtained were reversible and rapid, with a response time in the order of 5s. It is concluded that the bathing gas does not act as an oxidant or reductant but it helps to solvate the internal counterionic species, and leads to an increase in mobility.
Enzyme electrode for the determination of bilirubin
Authors: Fortuney Alain , Guilbault George G.
Published: May 2005

Bilirubin oxidase (EC 1.3.3.5) catalyzes the oxidation of bilirubin to biliverdin with the concurrent reduction of oxygen to hydrogen peroxide. A platinum electrode was prepared with an immobilized bilirubin oxidase membrane. Bilirubin was determined by monitoring the increase in hydrogen peroxide concentration from the enzyme reaction. The calibration plot for bilirubin shows linearity up to 300μM. The detection limit is 0.7μM.
Electrocatalysis and measurements of hydrazine compounds at glassy carbon electrodes coated with electropolymerized 3,4‐dihydroxybenzaldehyde films
Authors: Pamidi Prasad V. A. , Wang Joseph
Published: May 2005

Chemically modified electrodes exhibiting electrocatalytic response towards hydrazine compounds were prepared by electroxidation of 3,4‐dihydroxybenzaldehyde (3,4‐DHB) on glassy carbon electrodes. The surface‐confined quinone moiety accelerates the slow oxidation of hydrazine or its methylated analogs, and allows their convenient quantitation at very low potentials. Cyclic voltammetry offers useful insights into the catalytic behavior. The electrocatalytic response is evaluated with regard to pH, scan rate, applied potential, hydrazine concentration, flow rate and other variables. When used as flow‐injection detector, the 3,4‐DHB modified electrode yields an extremely low detection limit of 5 × 10 −8M (32 pg) hydrazine. Applicability to thick‐film sensor strips is also illustrated.
Voltammetric study of the immobilization of palladium at the surface of carbon paste electrodes
Authors: Lubert Karl‐Heinz , Guttmann Markus , Beyer Lothar
Published: May 2005

The immobilization of palladium at the surface of unmodified carbon paste electrodes is studied by cyclic voltammetry. Some features of the voltammetric behavior of palladium(II) at carbon paste electrode in chloride solution are elucidated. Through pretreatment at 0 V (vs. Ag/AgCl) palladium is bound at the surface of the carbon paste. The amount immobilized depends on the composition of the solution, polarization time, electrode potential and stirring. During an anodic scan the surface‐bound palladium is oxidized at about +0.6 V; the well‐shaped peaks can be utilized for the determination of the immobilized Pd. The detection limit is about 5 × 10−6 M Pd2+ after 5 min polarization at 0 V (vs. Ag/AgCl) with stirring (base electrolyte 1 M KCl, pH 5.5). The rather complicated influence of hydrogen ions on the reactions at the palladium/carbon surface is discussed. Palladium and hydrogen can be “deposited” simultaneously at the carbon paste surface through cathodic polarization. Electrode reactions related to the observed peaks are suggested.
Bienzyme sensors based on poly(anilinomethylferrocene)‐modified electrodes
Authors: Mulchandani Ashok , Wang Chia‐Lin
Published: May 2005

Amperometric bienzyme electrodes for glucose, lactic acid and glutamic acid were constructed using glucose oxidase, lactate oxidase and glutamate oxidase immobilized on a horseradish peroxidase‐poly(anilinomethylferrocene)‐modified glassy carbon electrode. In these bienzyme sensors hydrogen peroxide formed by the enzymatic reaction of glucose, lactic acid and glutamic acid with oxygen in presence of the appropriate enzyme was detected at −50 mV (vs. Ag/AgCl), by the horseradish peroxidase‐poly(anilinomethy1ferrocene)‐modified glassy carbon electrode. Because of the detection at a low applied potential, electroactive compounds such as ascorbic acid, uric acid and acetaminophen, did not interfere in analyses. The results of characterization studies of these bienzyme electrodes in terms of their, sensitivity, selectivity, linear detection range, precision, accuracy, operational lifetime stability, and long term storage stability are presented.
Iridium‐dispersed carbon paste enzyme electrodes
Authors: Wang Joseph , Rivas Gustavo , Chicharro Manuel
Published: May 2005

An highly selective first‐generation glucose biosensor, based on an iridium‐dispersed carbon‐paste transducer, is described. The iridium‐on‐carbon particles provide excellent electrocatalysis for both the reduction and oxidation of hydrogen peroxide. Such unique catalytic action offers convenient biosensing of glucose at very low operating potentials, where interfering reactions are negligible. Factors influencing the electrocatalytic and biocatalytic actions are elucidated, along with the analytical performance. Implications to other oxidase‐based amperometric electrodes are discussed.
Electrochemical study of the binding properties of a metallothionein I related peptide with cadmium or/and zinc
Authors: Mendieta Jesús , Rodríguez Adela Rosa
Published: May 2005

An electrochemical study, using differential pulse polarography, of the binding properties of the peptide Lys‐Cys‐Thr‐Cys‐Cys‐Ala Thionein Fragment [56–61] MT I (FT) with cadmium and zinc was performed. This molecule, intrinsic to the metallothionein structure, was chosen as a model of the Cd, Zn Metallothioneins ion exchange and binding properties. The influence of the addition of metal ions, cadmium and/or zinc was studied with different ratios of complexing ligand/metallic cations, FT/M(II). It is assumed that the main complex M(II)‐FT possesses a stoichiometry of 1:1, but probably two or more complexes co‐exist depending on the FT/M ratios. The equilibrium M + FT ⇌ MFT concerning the complexation equilibrium of formation and dissociation was investigated as a function of pH, going from acid to basic solution and vice versa in different mixtures: Cd:FT, Zn:FT and Cd:Zn:FT. The apparent stability constants of the complexes Cd‐FT, Zn‐FT were estimated at different pH values.
The influence of the carbon paste composition on the performance of an amperometric bienzyme sensor for L‐lactate
Authors: Spohn Uwe , Narasaiah Dontha , Gorton Lo
Published: May 2005

The influence of different additives on the performance of a bienzyme carbon paste electrode for the detection of L‐lactate was investigated. The influence of the pH during the adsorptive coimmobilization of lactate oxidase and horseradish peroxidase on heat pretreated carbon particles was determined in the presence and in the absence of polyethylenimine (PEI). In the absence of PEI the highest H2O2 and lactate sensitivities can be achieved after using a pHi of around 7. In the presence of PEI the response to background ratio can be increased considerably by using pHi values higher than 8.5. The lactate sensitivity is relatively independent of the pHi.

The influence of the additives poly‐L‐lysine, poly‐L‐arginine, spermine, and spermidine was also investigated. The use of positively charged poly‐aminoacids improves both the sensitivity/background ratio and the long‐term stability of L‐lactate and H2O2 detection.

Also the choice of both the carboneous powder and the pasting liquid has a considerable influence on the sensor characteristics. A heat treatment of the carboneous powder at 700° C for 15s improves the sensitivity of HRP modified CPEs in most cases. The replacement of the organic pasting liquid by organic solids, e.g., octadecane, heneicosane, and naphthene opens up a way to prepare robust and sensitive lactate sensors.

The considered influences of the carbon paste composition and the immobilization conditions were discussed both with respect to the H2O2 and the L‐lactate responses.
Stripping analysis combined on‐line with inductively coupled plasma‐atomic emission spectrometry and with inductively coupled plasma‐mass spectrometry
Authors: Zhou Feimeng
Published: May 2005

This review article describes the basic principles of combining stripping analysis (SA) on‐line with inductively coupled plasma‐atomic emission spectrometry (ICP‐AES) and with inductively coupled plasma‐mass spectrometry (ICP‐MS). Four applications are reviewed to demonstrate the utility and versatility of the combination of SA with ICP‐AES or ICP‐MS: (1) preconcentration of an analyte for enhanced sensitivity, (2) elimination of detrimental ICP‐AES or ICP‐MS matrix effects, (3) elemental speciation at trace levels, and (4) sensitive multielement determination. Factors influencing the analytical performance of the on‐line coupling of SA with ICP‐AES or with ICP‐MS are also discussed.
Voltammetric multichannel measurements using silicon fabricated microelectrode arrays
Authors: Paeschke Manfred , Dietrich Frank , Uhlig Albrecht , Hintsche Rainer
Published: May 2005

A modular voltammetric multichannel detection system has been developed for use in flow analysis. Two different types of multichannel potentiostats, an adjustable and a ground‐fixed potentiostat, are realized. Both types work with up to sixteen independent working electrodes at one chip electrode array and are controlled through a personal computer and a microcontroller. Simultaneous difference pulse and cyclic voltammetric procedures are realized. Platinum thin‐film array electrodes have been arranged on silicon wafers as pairs of interdigitated microband electrodes (interdigitated array electrodes; IDA) with an interelectrode gap in the submicrometer range. Furthermore the multichannel electrodes in a flow system were used to characterize the highly sensitive flow profiles and flow rate measurements using redox mediators. A brief description of applying the multichannel device for ‘window’ stripping of heavy metals is given.
Flow injection monitoring and analysis of mixtures of simazine, atrazine, and propazine using filter‐supported bilayer lipid membranes (BLMs)
Authors: Nikolelis Dimitrios P. , Siontorou Christina C.
Published: May 2005

This work describes a technique for the rapid and sensitive electrochemical flow injection monitoring and analysis of mixtures of the triazine herbicides simazine, atrazine and propazine using stabilized systems of filter‐supported bilayer lipid membranes (BLMs) composed of egg phosphatidylcholine (egg PC) and dipalmitoylphosphatidic acid (DPPA). Injections of herbicides were made into flowing streams of a carrier electrolyte solution and a transient current signal with a duration of seconds reproducibly appeared in less than two min after exposure of the lipid membranes to the herbicides. The magnitude of this signal was linearly related to the herbicide concentration, which could be determined at sub‐micromolar level. The mechanism of signal generation was related to a rapid adsorption of the triazine followed by a slow aggregative process of the herbicide at the surface of BLMs with a consequent rapid reorganization of the membrane electrostatics. Repetitive cycles of injection of herbicides have shown no signal degradation during each cycle. The time of appearance of the transient response was different for each triazine and increased to the order of simazine, atrazine and propazine which has allowed selective detection and analysis of these triazines in mixtures.
Zeolite‐modified electrodes: Analytical applications and prospects
Authors: Walcarius Alain
Published: May 2005

A review is presented dealing with the use of zeolite‐modified electrodes (ZMEs) for electroanalytical purposes (183 references). It includes an introduction to the zeolite molecular sieves, a short overview of zeolites and electroactive species used at electrochemical interfaces modified by the presence of zeolite particles, three aspects of the electroanalysis using ZMEs, including voltammetry, potentiometry and electrocatalysis. New prospects concerning the electrochemistry of ZMEs are also discussed.
Influence of the multilayer adsorption of n‐octanol and n‐decanol on electrooxidation of the radical anion of 3‐nitrophthalic acid
Authors: Matyjasiak Anna , Stroka Jadwiga , Galus Zbigniew
Published: May 2005

The electrooxidation of in situ produced electrolytically radical anion of 3‐nitrophthalic acid in various water—ethanol solutions containing 0.5 M NaCIO4, 0.05 M NaOH and inhibitor has been studied. The inhibition of the electrode kinetics in the presence of n‐octanol and n‐decanol, used as inhibitors, at relative concentrations not exceeding c/cs ≤ 0.5 could be interpreted in terms of the competitive monolayer adsorption of reactant, inhibitor and solvent on the electrode surface. At c/cs > 0.8, on the capacitance‐potential curves, a subtle minima caused by formation of two layers adsorbed on the mercury electrode were observed. The kinetics of the electrooxidation of the 3‐nitrophthalic acid anion radical was additionaly influenced by this multilayer. An equation which describes the inhibition of the electrode process by two adsorbed layers of inhibitor is presented and used in the estimation of the surface coverage in the second layer.
Chemically modified microelectrodes designed for the electrochemical determination of nitric oxide in biological systems
Authors: Bedioui Fethi , Trevin Stéphane , Devynck Jacques
Published: May 2005

Since the identification of nitric oxide (NO) as an endothelial‐derived relaxing factor, several research groups are now working to develop an understanding of the mechanism by which this free‐radical gas is synthesized, diffused and reacted from and within various cells and different biological tissues. Thus, it appears that measuring NO in biological models is very difficult because of its low concentration and fleeting existence. Indeed, NO directly reacts extremely fast with superoxide and other very active free radicals of biological importance. Most of the techniques for assaying NO release use indirect methods for estimating endogeneous NO, relying on measurements of secondary species. In fact, NO in biological systems may be directly assayed by three nonelectrochemical strategies (EPR, spectrophotometry and chemiluminescence) but these strategies suffer from being ex situ detection techniques with poor selectivity or sensitivity. The desire to measure a small amount of NO release in situ has led to an active area of research involving the design of microsensors and new amperometric microelectrode probes are now developed to detect NO. The use of electrochemistry as a potential way to do so is very promising and the reality is that surface electrode modification is needed to make the electrode material selective for NO. Therefore, the design of modified electrode surfaces using organized layers combined with microelectrodes is attractive as possible selective microsensors for the electrochemical detection of NO. A number of new amperometric approaches have reached this goal. This article consists of a critical review of electrochemical methods for the detection and determination of nitric oxide in biological materials to clarify some aspects of the reported microsensors.
Characterization of photopolymerized decyl methacrylate as a membrane matrix for ion‐selective electrodes
Authors: Ambrose Theresa M. , Meyerhoff Mark E.
Published: May 2005

Potentiometric ion‐selective sensors based on photopolymerized thin films of decyl methacrylate (DMA) crosslinked with hexanedioldimethacrylate (HDDMA) are described. The electrochemical response characteristics including slopes, selectivities, resistances and response times of several DMA‐based ion‐selective electrodes are reported and compared to those obtained using PVC‐based sensors. Sensors incorporating the nonspecific anion exchanger tridodecylmethylammonium chloride and the plasticizer dioctyl sebacate exhibit a Nernstian response to chloride with the expected Hofmeister selectivity pattern. Additional response data for potassium and carbonate selective sensors prepared with the electrically neutral ionophores valinomycin and p‐decyltrifluoroacetophenone, respectively, are also presented. The eflects of endogenous anionic sites arising from dissociated methacrylic acid impurities within the membrane matrix are discussed. The degree of site dissociation and its resulting contributions to the EMF response‐governing equilibria are considered in detail. It is shown that such sites must be electrically compensated (via addition of adequate lipophilic cationic sites) when preparing neutral‐ carrier based anion sensors but otherwise have no apparent effect on the sensing membranes' selectivity and performance.