Search

A rugged lead ruthenate pyrochlore (Py, Pb2Ru2O6O′) Nafion® 417 membrane catalyst (|NPy|) has been prepared by an in situ precipitation method and characterized by physico-chemical techniques. The Nafion® 417 membrane enhanced the Py crystallization to form a stable and continuous agglomerate-like structure in the |NPy| network. The cationic exchange characteristics of Nafion® 417 membrane was not fully suppressed after Py modification. Catalytic performance was demonstrated for the one pot and selective oxidation of benzyl alcohol to benzaldehyde via a perruthenate (RuO4−) intermediate with 30% H2O2 (as a sacrificial co-oxidant) in a triphasic condition (i.e. CH2Cl2/NPy/H2O2). Four repeated experiments with the |NPy| entailed a weight loss of ∼0.07% with virtually the same catalytic performance. With these inherent features, this membrane catalyst is useful in diverse research fields including organic synthesis, fuel cells, charge storage systems, etc.

Presented in this work is the first step towards an enzymeless/mediatorless glucose sensor. We first observed remarkable electrocatalytic oxidation of glucose using combinative ruthenium oxide (RuOx)-Prussian blue (PB) analogues (designated as mvRuOx-RuCN, mv: mixed valent) at ca. 1.1 V (vs. Ag/AgCl) in acidic media (pH 2 Na2SO4/H2SO4). Individual RuOx and PB analogs failed to give any such catalytic response. A high ruthenium oxidation state (i.e., oxy/hydroxy-RuVII, E°≈1.4 V vs. RHE), normally occurring in strong alkaline conditions at RuOx-based electrodes, was electrogenerated and stabilized (without any conventional disproportionation reaction) in the mvRuOx-RuCN matrix for glucose catalysis. Detail X-ray photoelectron spectroscopic studies can fully support the observation. The catalyst was chemically modified onto a disposable screen-printed carbon electrode and employed for the amperometric detection of glucose via flow injection analysis (FIA). This system has a linear detection range of 0.3–20 mM with a detection limit and sensitivity of 40 μM (S/N=3) and 6.2 μA/(mM cm2), respectively, for glucose. Further steps towards the elimination of interference and the extendibility to neutral pHs were addressed.

with0.3m KCl/HCl (optimized), adjusted to pH 2.Both methods re-sulted in almost similar electrochemical and catalytic function(verified with glucose, ethanol, and formaldehyde); but ap-proach 2 yielded a material with a more stable cyclic voltam-metric (CV) response and hence this approach was uniformlyadopted throughout these stud-ies.Classical RuOx and PB wereprepared using RuCl

The electrochemical redox behavior of the polynuclear mixed valence ruthenium oxide cyanometallate complexes (mvRuOxMCN, M=Fe, Cr, Ni, Cu, Ru and Pt) have been systematically studied in this report by using three redox sensitive organic probes of glucose, ethanol and formaldehyde. The results were interpreted by the well-established ruthenium oxide and Prussian blue chemistry. The mvRuOxMCN, under the category of Ru-based Prussian blue analogue, was found to possess superior electrocatalytic activity than either ruthenium oxide or Prussian blue in acidic mediums. The electrogenerated oxy/hydroxy-RuVII state (at +1.1 V vs. Ag/AgCl) was unusually stabilized in the mvRuOxMCN matrix without any disproportion reaction in acidic environments. In contrast to those of earlier studies, possible structure in terms of the RuIII/IINCMand RuIII/IIORuVII/VIsites was proposed here. Enzyme-less analytical detection of glucose in acidic conditions was first time demonstrated with sensitivity comparable to that of ruthenium oxide-based electrodes in alkaline solutions.

Zinc pyrithione (ZPT) is an antibacterial and antifungal reagent that is often utilized for the antidandruff activity in hair-care shampoos with a composition level up to 1% in the formulation. It has some adverse effects to human and animal if consumed orally. A disposable type of cobalt phthalocyanide modified screen-printed carbon electrode (CoPc/SPE) in couple with flow injection analysis (FIA) was developed for easy and selective analysis of ZPT in commercial hair-care products. Under the optimized FIA conditions, the CoPc/SPE yielded a linear calibration plot in the window of 6-576muM with sensitivity and detection limit of 1.65nAmuM(-1) and 0.9muM (i.e. 1.42pg in 5mul sample loop), respectively, in 0.1M KOH solution at an applied potential of 0.3V versus Ag/AgCl. Since the approach is simple, easy, selective, and inexpensive, it offers a potential application of daily ZPT analysis in hair-care products.

Industrial waste cinder (CFe*) has been utilized as a stable anchoring matrix for self-assembling of Fe(CN)6 3 as hybrid Prussian blue units (PB, *Fe 3 Fe II (CN)6) on a screen-printed carbon electrode (SPE) for efficient catalytic applications. The waste cinder was found to be a composite of calcium and iron silicates similar to glass matrix by Xray photoelectron spectroscopic (XPS) study. The hybrid PB formations were confirmed by both FT-IR and electrochemical methods. Most importantly, the free iron (Fe*) ion bound to the non-bridging oxygen terminals of the silicates was found to play a key role in the PB formation. The self-assembled PB hybrid on the cinder-modified screen-printed electrodes (designated as PBCFe*-SPE) improved linear detection range and sensitivity for H2O2 mediated oxidation than those obtained at a classical PB-SPE in 0.1 M, pH 2 KCl/HCl base electrolyte at 0.0 V (vs. Ag/AgCl) by amperometric batch analysis.

Natural iron-intercalated clay (nontronite, SWa-1) was converted into a more efficient catalyst by formation of lead ruthenate pyrochlore (Py, Pb2Ru2−xPbxO7−y) directly inside the matrix. The new material can take advantage of the electrocatalytic properties of both Py and nontronite and can even generate new catalytic active sites due to interaction of Py and nontronite. The combination of these two interesting catalysts results in a more reactive electrode (designated as SWa-1/PyCME) for electroanalytical applications. The preparation and characterization of the SWa-1/PyCME as well as its electrocatalytic behavior toward the oxidation of dopamine are described in this study. Surface saturation kinetics in terms of Michaelis-Menten kinetics suited well the oxidation of dopamine on this modified electrode. Under optimized conditions, the detection limit (S/N= 3) was 0.54 nM by square-wave voltammetry.

We report here a new electrochemical method for the selective detection of ultratrace amount of arsenite (AsO(2)(-), As(3+)) using a Prussian blue-modified screen-printed electrode (designated as PBSPE) by flow injection analysis (FIA) in 0.1 M, pH 4 KCl/HCl carrier solution. The Prussian yellow/Prussian blue redox couple of the PBSPE was found to mediate the As(3+) oxidation. Various factors influencing the determination of As(3+) were thoroughly investigated in this study. Under the optimized FIA conditions, a linear calibration plot in the range of 50 nM-300 microM with a detection limit (S/N = 3) of 25 nM (i.e., 64.9 pg in 20-microL loop) was observed at an operation potential of +0.6 V vs Ag/AgCl. The sensitivity was good enough to detect arsenite at levels lower than the current EPA standard. This modified electrode showed good resistance to interference from common ions, especially Cl(-), which is generally considered as a major interference in the determination of As(3+) by ICPMS. The practical utility of the PBSPE to detect As(3+) was demonstrated in "blackfoot" disease endemic village groundwater from the southwestern coast area of Taiwan (Pei-Men).

A silica sol-gel glass-coated ferricyanide-doped Tosflex-modified screen-printed electrode (designated as SG/FeCN-Ts/SPE) was used for the mediated oxidation of ascorbic acid in neutral pH. The sol-gel overlayer was found to stabilize the Fe(CN)-Tosflex system without any foul-off and deterioration behavior through chemical interaction between the hydrophilic sites of Tosflex and oxy- and/or -hydroxy surface functional groups of silicate. The electrochemical mediation of ascorbic acid was found to follow the Michaelis-Menten kinetic pathway. The SG/FeCN-Ts/SPE was very stable for repetitive measurements by flow injection analysis at 0.3 V (vs. Ag/AgCl). A linear calibration plot was obtained for ascorbic acid determination up to 300 μM with sensitivity and detection limit (S/N=3) of 2.85 nA/μM and 46 nM, respectively. The system also showed tolerable interference to uric acid, urea and carbohydrates and was used for the determination of ascorbic acid in human urine, clinical tablet and apple juice.

This review article updates recent developments in chemically modified electrodes (CMEs) towards analytical applications for the year of 2000–2002 with 179 references. The broad topics are subdivided into four main categories: i) physisorption/chemisorption, ii) covalently linked, iii) homogenous (uniform) multilayer and iv) heterogeneous (non-uniform) multilayer CMEs. The criteria for the preparation of CMEs in elecrocatalytic systems are clearly described in Section 1. Some of the encouraging results related to Au-nanoparticles for DNA detection and new ceramic carbon, carbon nanotubes, copper-plated screen-printed and Nafion/lead ruthenate pyrochlore CMEs for catalytic application were especially discussed in this review.

In the present work, a new strategy involving the addition of CTAB at its critical micelle concentration was developed to improve the electrochemical properties of the cinder/PB-modified screen-printed electrode (designated as cinder/PB-SPE) in the detection of H 2 O 2 by flow injection analysis (FIA). Such new PB hybrids derived from cinder have remarkable stability even under strong hydrodynamic stress. The cylindrical CTAB micelles formed at the 2 n d critical micelle concentration can effectively promote the PB redox behavior. Under optimized conditions with pH 7 PBS + 7 mM CTAB as carrier solution in FIA, a linear calibration was obtained up to 25 μM H 2 O 2 with slope, regression coefficient, and detection limit (S/N = 3) of 1.03 A/Mcm 2 , 0.995, and 4.02 μM respectively. Interferences by direct electrochemical oxidation of easily oxidizable substances can be prevented due to the low detecting potential of the working system.

Screen-printed silver electrodes (AgSPEs), without chemical modification, has been investigated as disposable sensors for the measurement of trace levels of Pb 2+ . Potential segment analysis indicates that the formation of underpotential and bulk depositions of Pb is not strongly coupled on the AgSPE. The possibility of determining Pb 2+ at trace levels using the reversible underpotential deposition peak was examined by square-wave anodic stripping voltammetry without removal of oxygen. Under the optimized analytical conditions, the obtained sensitivity, linearity, and detection limit are 0.355 μA/ppb, 5–80 ppb ( r =0.9992), and 0.46 ppb (S/N=3), respectively. The electrode is quite stable for repetitive measurements. The interference effect was thoroughly studied with various metals and no significant change in current was found in the determination of 5 ppb Pb 2+ . The practical applications were demonstrated to measure trace Pb 2+ in natural waters.

Flow injection analysis (FIA) of ultratrace sulfide has been demonstrated on a screen-printed carbon electrode modified with industrially waste cinder/hexacyano cobaltate (CoHc) hybrid (designated as cinder/CoHcSPE) in pH 2 NH4Cl (0.1 M)/HCl solution at 0 mV (vs. Ag/AgCl). Hybridization of CoHc was achieved through bimetallic formation of FeIII[CoIII(CN)6] in the *FeIII[CoIII(CN)6] in the *Fe-enriched industrially waster cinder modifier. Possible mediated electrocatalytic oxidation of sulfide by higher oxidation state of Co in the hybrid-bimetallic complex is proposed for the system. Under the optimized conditions, the calibration plot is linear up to 2.08 μM with slope, regression coefficient, and detection limit (S/N=3) of 6.19 A/μM, 0.9985, and 12 nM, respectively. Interferences by direct electrochemical oxidation of easily oxidizable substances can be prevented due to the low detecting potential of the working system.

Selective detection of o-diphenols (e.g., catechol, dopamine, and pyrogallol) in the presence of simple phenols, m- and p- derivative diphenols, and ascorbic acid has been demonstrated on copper-plated screen-printed electrodes (CuSPEs) in pH 7.4 phosphate buffer solution. The CuSPE showed an unusual catalytic response at -0.05 V versus Ag/AgCl selectively to o-diphenolic compounds. The o-diphenols can thus be determined amperometrically through direct electrochemical oxidation in low potentials (approximately 0 V), where the CuSPE is much less subject to interfering reactions. Such a catalytic phenomenon cannot be observed on conventional Pt and glassy carbon electrodes. The selective mechanism is explained in terms of the formation of cyclic five-member complex intermediate (Cu(II)-o-quinolate). Most important of all, the common drawbacks of electrode fouling through polymerization were completely overcome in this system.

Nontronite/cellulose acetate-coated glassy carbon electrodes (NCA/GCEs) were evaluated for the preconcentration and electroanalysis of Cu2+ in ammoniacal medium by square-wave voltammetry. The NCA/GCEs exhibit good accumulation ability for the [Cu(NH3)4]2+ complex ion via the ion-exchange ability of nontronite. A permselective membrane, cellulose acetate, was applied to strengthen the mechanical stability of the nontronite coating on GCE and to prevent the interference from surface-active compounds. The experimental parameters were studied in detail. The NCA/GCEs show good reproducibility with a relative standard deviation of 2.83% for 15 successive determination of 20 ppb Cu2+. Under optimized conditions, a linear calibration plot was obtained up to 4 ppm Cu2+ with a detection limit (S/N=3) of 1.73 ppb after a preconcentration time of 2 minutes in pH 10 ammonia solution. The practical utility of the NCA/GCEs was illustrated by the measurement of Cu2+ in tap water, groundwater, and pond water.

This is the first report on studies of the underpotential deposition of Pb (upd-Pb) on a disposable screen-printed silver electrode (AgSPE, non-single crystalline surface). The dependence of upd-Pb and bulk Pb deposition (bulk-Pb) on potential scan rate (ν) was demonstrated for the AgSPE in pH 3 KNO3/HNO3 solutions. At ν=20 mV s−1, the extent of formation of reversible upd-Pb was ∼15 times less than that of irreversible bulk-Pb. However, for ν>100 mV s−1, only the upd-Pb was observed. Scanning electron microscopic (SEM) analysis speculated 3D-nucleation (hcp) of bulk-Pb on the AgSPE at low scan rate (ν=1 mV s−1). On the other hand, at a faster scan rate (ν=300 mV s−1), no marked crystallites were obtained. By interpretation with the CV results, the later case was proved to be formation and complete stripping of the upd-Pb on the AgSPE and this property was further utilized for analytical application. The nearly reversible behavior of the upd-Pb process at the disposable AgSPE is a judicious choice for the effective stripping analysis of Pb by square-wave voltammetry.

A preanodized nontronite-coated screen-printed electrode (NSPE ∗ ) was developed for the sensitive detection of the pesticide amitrole by square-wave voltammetry (SWV) and flow injection analysis (FIA). The preanodization process was essential to improve the sensitivity because of the existence of higher iron oxidation state in the interlayer of nontronite clay. Factors influencing the SWV and FIA responses were evaluated in this study. Under optimized conditions, the calibration curve showed a linear range up to 300 and 500 μM for SWV and FIA, respectively, in pH 4.5 PBS. The detection limit (S/N=3) was 0.33 μM in SWV and 0.07 ng in a 20 μl sample loop by FIA. The high precision and sensitivity of the method offers an easy route for direct determination of amitrole.

Prussian blue (PB) is electrochemically trapped directly on the interlayer resume of cinder-containing carbon paste electrodes (cinder/PB-CPEs). A UV-visible spectroscopic study gives supportive evidence for the formation of PB in the cinder matrix. This hybrid cinder/PB-CPE shows similar redox behavior to that of electrochemically synthesized PB film on the surface of a glassy carbon electrode. Nevertheless, the physical and electrochemical activities are comparatively superior over the classical PB electrodes. The electrochemical features, such as, high surface excess, positive site-site interaction parameter together with low film resistance result in good electrochemical activity and stability of the cinder/PB-CPE. The cinder/PB-CPE is further utilized for the mediated oxidation of nitrite. Mechanistic parameters, such as, anodic transfer coefficient, Tafel slope, and standard heterogeneous second order rate constant were evaluated as 0.52, 114.3 mV/decade, and 8.36 mol−1 dm3 s−1, respectively. The catalytic scheme was then extended to analytical applications with a linear range up to 1600 μM (regression coefficient=0.9996) and a detection limit (S/N=3) of 3.36 μM.

The application of potentiometric stripping analysis (PSA) to the trace determination of thallium(III) at a poly(4-vinylpyridine)=mercury film electrode (PVP=MFE) is demonstrated. Thallium(III) is preconcentrated as the anionic form, [TlCl4] ˇ , by the ion-exchange effect into the PVP=MFE. The high solubility of thallium in mercury subsequently helps to increase the accumulation effect. The variable factors influencing the PSA response are thoroughly explored and optimized. The PVP=MFE shows good resistance to interferences from surfaceactive compounds and common ions with an excellent sensitivity by PSA over square-wave voltammetry (SWV). With 1 min of accumulation time, the calibration plot was found to be linear up to 100 ppb with a detection limit of 0.064 ppb (S=Na 3). The analytical utility was demonstrated by application to various water samples.

Electrocatalytic oxidation of cysteine (CySH) at Nafion/lead ruthenate pyrochlore (Py) chemically modified electrodes was thoroughly studied. Electrochemical ac impedance spectroscopy analysis indicated the formation of Py microparticles in the interfacial galleries of Nafion. Experiments with benchmark systems of Fe(CN)63-/4- and Ru(bpy)2+/3+ reveal the suppression of Nafion's anionic character after the in situ precipitation of Py. Michaleis−Menten-type kinetics with the rate determination step of CyS−Py−RuVI → Py−RuIV + CyS−SCy was proposed for this catalytic oxidation. The electrocatalytic behavior is further developed as a sensitive detection scheme for CySH by square-wave voltammetry (SWV) and flow injection analysis (FIA). Under the optimized conditions, the calibration curve is linear up to 560 μM with a detection limit (signal/noise 3) of 1.91 μM in SWV. The detection limit can be improved to 1.70 nM (i.e., 24.22 ng in a 20-μL sample loop) in FIA. This is the lowest value ever reported for direct...

The electrochemical redox behavior of lead–ruthenium oxide pyrochlore catalyst (Pb2Ru2−xPbxO7−y, x=0.25) was systematically studied and possible ruthenium redox species were determined by probing with formaldehyde and glucose oxidation reactions using a PVC/Pb2Ru1.75Pb0.25O7−y composite electrode. Trasatti’s surface charge formalism was applied to calculate the different accessible interfacial surface charges. Both the outer/inner and anodic/cathodic charge ratios were found very different to those of pure RuO2 electrode. It is important to note that higher cathodic charges were noticed in all scan rates (v) and pHs for Pb2Ru1.75Pb0.25O7−y. The calculated pHPZC of 3.9 from the electrochemical measurements match exactly with that of earlier titrimetric result. The electrocatalytic mediated reactions were demonstrated with Ru3+/4+ assisted oxygen reduction reaction and Ru4+/6+ assisted dopamine oxidation using a Nafion/Pb2Ru1.75Pb0.25O7−y composite electrode. Rotating disk electrode technique was adopted to derive kinetics and mechanism of these two catalytic reactions.

Electrocatalytic oxidative cyclization of dithiothreitol (DTT(SH)2) to a disulfide product was demonstrated on a Nafion/lead-ruthenium oxide pyrochlore chemically modified electrode (NPyCME). The process at the NPyCME with DTT(SH)2 is similar to the behaviour of protein in a disulfide linkage, which can be demonstrated by product analysis using HPLC coupled with UV spectroscopy. A possible electrocatalytic mechanism for DTT(SH)2 oxidation to dihydroxydithiane [i.e. cyclized DTT(S-S)] on the NPyCME was proposed in terms of Py-Ru(IV)/Py-Ru(VI) redox active sites. This physical aspect was further utilized for high precision analytical assays using flow injection analysis (FIA), with a linearity up to 50 microM and a detection limit (S/N = 3) of 28 nM (8.64 pg) in a 20 microL sample loop. This is the most sensitive method ever reported for DTT(SH)2 detection assays. The interference from dissolved oxygen, disulfide and glucose is almost negligible. The present method offers an easy route for extension to redox-related protein studies.

Tosflex, a perfluoro-anionic exchange membrane, is not studied as much as Nafion for electroanalytical applications. In this study, electrocatalytic oxidation of ascorbic acid (AA) was demonstrated using a ferricyanide-doped Tosflex-modified electrode in pH 5 phosphate buffer solution. The modified electrode showed good stability over the studied pH range of 2–12. The electrocatalytic oxidation of AA on the modified electrode follows the surface-saturation kinetics in terms of Michaelis-Menten (MM) mechanism. The analytical estimations were performed amperometrically under hydrodynamic conditions at an applied potential of 300 mV versus Ag/AgCl. A linear response was observed in the range of 0–50 μM with a regression coefficient of 0.998. Keywords: Tosflex, Fe(CN)63−/4−, Ascorbic acid, Mediated oxidation

Ruthenium dioxide electrodes, prepared on a Pt substrate using coatings of PVC-RuO2 mixed in THF (designated as RuO2-PVC film electrode) have been studied for their redox behaviour in 1 M NaOH using variable scan cyclic voltammetry. The various redox transitions in the oxidation state of the central metal ion are characterized using electrochemical parameters such as peak potential, peak current, and surface charge. The effect of oxide preparation temperature, in the range 300–700 °C, on the redox characteristics has also been studied and correlated with the electrochemically active surface area (as measured using small amplitude cyclic voltammetry) and the true surface area (by the BET method).

A Cu/Hg-plated screen-printed electrode (CMSPE) was developed for trace Pb(II) determination by square-wave anodic stripping voltammetry. The intermetallic property of lead with copper in mercury was utilized to increase the sensitivity of Pb(II) detection. The calculated transfer coefficient value for the Pb(II)/Pb redox process on the CMSPE is ∼0.5 representing the ideality of the system for Pb(II) detection. Systematic investigations were made to optimize the Cu–Hg plating condition on SPE towards the Pb(II) signals in terms of Cu/Hg ratio, plating potential, and plating time. The optimum conditions for electrochemical and square-wave parameters were also evaluated. The calibration curve was linear in the range of 0–100 ppb Pb(II) with a detection limit of 0.81 ppb ( S / N =3) for 60 s preconcentration time. The analytical utility of the CMPSE was demonstrated by applying to various water samples.

Natural iron-intercalated clays and waste cinder (from steel industry) were converted into an efficient catalyst by electrochemical formation of Prussian blue (PB) directly inside the matrix. The basic electrochemical features for the PB-modified electrodes were investigated by means of cyclic voltammetry technique, in terms of Efwhm, surface charge (q), surface excess (Γ), site-site interaction model, and film resistivity (Rf), etc. The iron intercalated PB electrodes show superior electrochemical activity and stability over the classical GCE/PB electrodes and were analyzed by the interaction parameter ‘r’. The more efficient electrocatalytic function of the iron intercalated PB electrodes than the GCE/PB was demonstrated with guanine oxidation reaction.

An enzymeless sensor based on a Nafion/lead-ruthenium oxide pyrochlore modified electrode (NPME) is described for the sensitive estimation of hypoxanthine (Hx) using square-wave voltammetry. The NPME showed a marked catalytic activity towards the oxidation of Hx. The quasi-steady-state oxidation current for Hx on the NPME provided a crucial mechanistic indication that the process follows the Michaelis-Menten kinetics. In brief, the process involves the formation of a substrate-catalyst complex that subsequently decomposes to form product and precatalyst; the latter can afterwards be regenerated electrochemically. The Michaelis-Menten constant (Km), catalytic rate constant (kc), heterogeneous electrochemical rate constant (ke′), and the reaction order (m) were evaluated. The experimental parameters were optimized for analytical estimation of Hx and the detection limit (S/N=3) was found to be as low as 0.75 µM. The use of the proposed sensor to estimate the fish freshness is demonstrated with very good reproducibility with a relative standard deviation of 2.4 % for ten successive measurements.

A disposable copper-plated screen-printed carbon electrode (CuSPE) was developed for the determination of hydrogen peroxide by flow injection analysis (FIA) at ambient temperature without deoxygenation. Cyclic voltammetry on the CuSPE in pH 7.4 phosphate buffer solution showed the growth of CuO and Cu2O. A well-defined reduction signal corresponding to the mediation of CuO and Cu2O occurred in the presence of hydrogen peroxide. The mechanistic study revealed that the reduction is a coupled-chemical reaction mechanism with the operation of pseudo-first order kinetics with respect to the concentration of Cu2O. The calculated electrochemical rate constant (ke) from Laviron’s model is 13.7 s−1. Systematic investigations were made to optimize the experimental parameters for hydrogen peroxide detection by FIA. With a poised potential of −0.3 V versus Ag/AgCl and a flow rate of 2 ml min−1, the calibration curve was found to be linear up to 200 μM hydrogen peroxide with a detection limit of 0.97 μM (S/N = 3). The CuSPE is fairly stable for repetitive measurements.

An electrochemically oxidized glassy carbon electrode was found to work excellently in the trace determination of Pb(II) using square-wave anodic stripping voltammetry. The associated phenomena were unravelled using chronocoulometry, linear scan voltammetry and electrochemical impedance spectroscopy. The chronocoulometry results showed that the double layer charge enormously increased on preanodization due to the creation of phenolic and quinolic oxide functional groups on the surface. The ac impedance analysis indicated that the duplex-layer model could illustrate the oxidized glassy carbon electrode behaviour quantitatively. The experimental factors, including preanodization condition, square-wave parameter, supporting electrolyte and pH, were optimized. Using the optimum parameters, the calibration curve was constructed and the detection limit was found to be 0.7 ppb (S/N = 3). The electrode is quite stable for repetitive measurements. The practical application was demonstrated to estimate trace Pb(II) in groundwater with very good precision.

A sensitive voltammetric method is developed for the determination of parathion (fNO2) using a Nafion 1 -coated glassy carbon electrode. In this method, parathion is first irreversibly reduced from fNO2 to fNHOH. The reversible peaks at around a0.33 V (versus Ag/AgCl) corresponding to a two-electron oxidation/reduction of hydroxylamine (fNHOH) to the nitroso (fNO) derivative were used for detection with square-wave voltammetry. The experimental parameters, such as, pH, film thickness, preconcentration potential, preconcentration time, and square-wave voltammetric parameters were optimized. Using this method, a linear calibration curve for parathion was obtained up to 15 mM range in pH 1.1 citrate buffer solution with a detection limit (S/Na 3) of 50 nM. # 1999 Elsevier Science B.V. All rights reserved.

A copper-metal enriched printed-circuit board waste modified screen-printed electrode has been demonstrated for the sensitive electroanalysis of a tyrosinase biosynthesis-inhibiting cosmetic agent,...

Fits like a glove: Separationless and selective electrochemical oxidation of the α-naphthol (α-NAP) isomer yields naphthoquinone species on the surface of multiwalled carbon nanotubes, which can further catalyze the electro-oxidation of NADH and hydrazine at different potentials. The β-NAP isomer failed to show any such electro-oxidation.

isobutene by b-H-elimination: M. G. Klimpel, J. Eppinger, P. Sirsch, W. Scherer, R. Anwander, Organometallics 2002, 21, 4021. [23] E. B. Coughlin, L. M. Henling, J. E. Bercaw, Inorg. Chim. Acta 1996, 242, 205. [24] D. Stern, M. Sabat, T. J. Marks, J. Am. Chem. Soc. 1990, 112, 9558. Ansa-ligand rearrrangement and formation of hydridebridged TMflyover∫dimers seems to have drastic consequences on the catalytic activity in olefin polymerization. For example, the reaction of [{Et2Si(C5H4)(3,4-Me2-C5H2)Lu(m-H)}2] (5) with ethylene, propylene, and 1-hexene gave quantitatively m-hydride/m-alkyl mono-insertion products at ambient temperature. However, similar complexes such as 6 were also shown to be highly efficient in the block copolymerization of ethylene and polar monomers.[3] [25] A comprehensive survey of the 1H NMR chemical shifts (d1⁄4 1.85±8.31 ppm) and 89Y-1H coupling constants (23.8±35.3 Hz) of dimeric yttrium hydrido complexes is presented in: K. C. Hultzsch, P. Voth, K. Beckerle, T. P. Spaniol, J. Okuda, Organometallics 2000, 19, 228. [26] Compound 4a (C52H62O2Si2Y2¥2C6D6) crystallizes from benzene in the monoclinic space group P21/c with a1⁄4 11.7875(2), b1⁄4 14.0396(3), c1⁄4 16.8378(4) a, b1⁄4 104.2053(12)8, V1⁄4 2701.31(10) a3, and 1calcd1⁄4 1.364 gcm 3 for Z1⁄4 2. Data were collected at 193 K on a Nonius Kappa-CCD system. The structure was solved by Patterson methods, and least-square refinement of the model based on 3682 reflections (I> 2.0s(I)) converged to a final R11⁄4 4.0% (wR21⁄4 8.1%). Except H(1), all hydrogen atoms were placed in calculated positions. H(1) was located in difference Fourier maps and refined with isotropic thermal parameters. CCDC-188842 (4a) contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB21EZ, UK; fax: (þ 44)1223-336033; or deposit@ccdc.cam.ac.uk). [27] a) N. Hˆck, W. Oroschin, G. Paolucci, R. D. Fischer, Angew. Chem. 1986, 98, 748; Angew. Chem. Int. Ed. Engl. 1986, 25, 738; b) K. Qiao, R. D. Fischer, G. Paolucci, J. Organomet. Chem. 1993, 456, 185. [28] W. J. Evans, D. K. Drummond, T. P. Hanusa, R. J. Doedens, Organometallics 1987, 6, 2279. [29] W. P. Kretschmer, S. I. Troyanov, A. Meetsma, B. Hessen, J. H. Teuben, Organometallics 1998, 17, 284. [30] a) K. C. Hultzsch, T. P. Spaniol, J. Okuda, Angew. Chem. 1999, 111, 163; Angew. Chem. Int. Ed. 1999, 38, 227; b) S. Arndt, P. Voth, T. P. Spaniol, J. Okuda, Organometallics 2000, 19, 4690. [31] R. Duchateau, C. T. van Wee, A. Meetsma, P. T. van Duijnen, J. H. Teuben, Organometallics 1996, 15, 2279. [32] T. I. Gountchev, T. D. Tilley, Organometallics 1999, 18, 2896. [33] J. P. Mitchell, S. Hajela, S. K. Brookhart, K. I. Hardcastle, L. M. Henling, J. E. Bercaw, J. Am. Chem. Soc. 1996, 118, 1045. Photocatalytic Oxidation

Polyaromatic hydrocarbon (PAH) oxidation: PAHs, which are considered major environmental pollutants, are carcinogenic, and cannot be electrochemically oxidized on conventional electrodes (gold, platinum, and glassy carbon), can be electrochemically oxidized on multiwalled carbon nanotube surfaces at a potential of 1 V versus Ag/AgCl at pH 7. This results in the formation of stable surface-confined quinone systems (see scheme; AN = anthracene; AQ = anthraquinone).

The aerobic oxidation of primary amines to their respective nitriles has been carried out at room temperature using a highly reusable nanocrystalline ruthenium oxide pyrochlore Nafion composite catalyst (see figure).

A hybrid polynuclear nickel hexacyanoferrate (NiHCFe)/graphitized mesoporous carbon- (GMC-) modified glassy carbon electrode (GCE/NiHCFe@GMC) has been prepared by a sequential method using electrodeposited Ni on a GMC-modified glassy carbon electrode (GCE/Ni@GMC) as a template and [Fe(CN)6]3−as anin-situchemical precipitant, without any additional interlinking agent. Physicochemical and electrochemical characterizations reveal the presence of NiHCFe units within the porous sites of the GMC. The GCE/NiHCFe@GMC electrode showed highly stable and well-defined redox behaviors with surface-confined electron-transfer mechanism in a pH 7 phosphate buffer solution. The GCE/NiHCFe@GMC showed about 20 times enhancement in hydrazine oxidation peak current along with 500 mV reduction in overpotential over the corresponding unmodified GCE/GMC. Hydrazine calibration plots by CV and amperometrici-tmethods were linear up to 1 mM and 220 μM with current sensitivity values of 15.86 μA/mM and 7.37 nA/μM, respectively. Calculated detection limit by the amperometrici-tmethod was 23.2 nM. The hybrid GCE/NiHCFe@GMC exhibits remarkable tolerance to important industrial and biological interferents. Finally determination of hydrazine in cigarette smoke sample was successfully demonstrated.

The electrocatalytic oxidation of cysteine (CySH) to cystine (CyS-SCy) was noticed on the Nafion-ruthenium oxide pyrochlore chemically modified electrode. The electrocatalytic oxidation was mediated by the RuVI/IV redox sites in the oxide pyrochlore network in terms of the Michaelis-Menten kinetics. The obtained heterogeneous catalytic rate constant (kc) and transfer coefficient (α) are 6.33 s−1 and 0.99, respectively.

An artificial enzyme analogue of Nafion/lead-ruthenium oxide pyrochlore (Py) chemically modified electrode (NPyCME) is synthesized by in situ precipitation through blocking of Nafion’s hydrophilic zones. The catalytically active Py sites covered with a hydrophobic core of Nafion resemble an enzymatic structure. Moreover, the NPyCME obeys the Michaelis-Menten mechanism for the oxidation of many organic and biological molecules. This Account highlights aspects of the preparation, characterization, and application of the NPyCME.

Tranexamic acid (TA) is an important reagent in cosmetic skin-whitening formulation and a drug for the inhibition of plasminogen to plasmin in blood. Since there is no chromophore in tranexamic acid molecule to enable direct analysis by UV–visible absorption spectrophotometry, derivatization is thus required by excluding use of UV or fluorescence detection. We report here a relatively simple electrochemical TA detection method by using a barrel plating nickel electrode. Chromatographic separation was performed on a Hamilton PRP-X100 anion-exchange column (150 mm × 4.1 mm i.d., 10 μm particle size) with a (85:15, v/v) mixture of 0.1 mol l −1 NaOH and acetonitrile as mobile phase and pumped at a flow rate of 0.9 ml min −1 . By detecting at +0.55 V vs. Ag/AgCl, the calibration plot was linear in the concentration window of 3–1000 ppm with regression coefficient and detection limit (S/N = 3) of 0.9993 and 0.13 ppm (0.84 μmol l −1 ), respectively. Successive injections ( n = 10) of 50 ppm tranexamic acid showed a R.S.D. value of only 0.3% indicating good reproducibility of the proposed system. The method was successfully applied to the analysis of the content of tranexamic acid in cosmetic products and proved to be suitable for rapid and reliable quality control.

Nanostructured molecular film containing the (micro-hydroxo)bis(micro-carboxylato) diruthenium(III) units, [RuIII2(micro-OH)(micro-CH3COO)2(HBpz3)2]+ ({RuIII2(micro-OH)}), was prepared by an in situ conversion of its micro-oxo precursor, [RuIII2(micro-O)(micro-CH3COO)2(HBpz3)2] ({RuIII2(micro-O)}), in a Nafion membrane matrix, where HBpz3 is hydrotris(1-pyrazolyl)borate. The conversion procedure results in fine nanoparticle aggregates of the {RuIII2(micro-OH)} units in the Nafion membrane (Nf-{RuIII2(micro-OH)}), where an average particle size (4.1 +/- 2.3 nm) is close to the Nafion's cluster dimension of approximately 4 nm. Chemically modified electrodes by using the Nafion molecular membrane films (Nf-{RuIII2(micro-OH)}-MMFEs) were further developed on ITO/glass and glassy carbon electrode (GCE) surfaces, and a selective reduction of nitrosonium ion (NO+), presumably through reaction of a {RuIIRuIII(micro-OH)} mixed-valence state with HNO2, was demonstrated without interference by molecular oxygen in an acidic aqueous solution. The Nf-{RuIII2(micro-OH)}-MMFEs are stable even in a physiological condition (pH 7), where the naked {RuIII2(-OH)} complex is readily transformed into its deprotonated {RuIII2(micro-O)} form, demonstrating an unusual stabilizing effects for the {RuIII2(micro-OH)} unit by the Nafion cluster environment.

An electrochemical cell coupled with disposable screen-printed electrodes (SPEs) that is specifically designed for use in flow injection analysis (FIA) is described in this study. The cell is made of foldable polyoxymethylene (acetal) thick platelets with the bottom portion consisting of a cavity track to drag the SPEs in position and the top portion having predrilled T-like holes to arrange the Ag/AgCl reference electrode and stainless steel inlet & outlet. An "O ring" is suitably fixed on the top of the working electrode to form a thin-layer space where the electrochemical reaction can take place. Hydrodynamic characterization was validated by using a benchmark hexacyanoferrate redox couple. The results of practical analysis of glucose in human plasma clearly demonstrate the characteristics and applicability of the proposed wall-jet electrochemical cell in FIA.

We report here a highly accurate and efficient method for blood lead analysis (BLA) through the use of a disposable electrode. A new type of mercury-plated preanodized screen-printed carbon electrode, together with a thallium(III) internal standard, simplifies calibration and gives easily quantifiable signals for accurate BLA. A preanodization procedure improves the preconcentration ability of the working electrode through the effect of lead (Pb) complexing with an electrogenerated surface functional group, mainly >C=O. Under optimized conditions, the ratio of the anodic stripping peak currents of Pb and Tl (i.e., i(Pb)/i(Tl)) is linear against [Pb] in the window of 1-300 ppb with a correlation coefficient and detection limit (signal-to-noise ratio=3) of 0.999 and 0.23 ppb, respectively. This approach was used to analyze blood samples (n=55) from workers at a local battery factory. The results are consistent with those obtained from graphite furnace atomic absorption spectroscopy and confirm the applicability of the proposed method.

A disposable copper nanoparticle-plated screen-printed carbon electrode (designated as Cun-SPE(100-nm)) provides a new material for the determination of native amino acids. All 20 underivatized amino acids can be sensitively determined at 0.0 V vs. Ag/AgCl in pH 8 phosphate buffer solution. The precisely controlled copper nanoparticles can boost up the CuIIO/CuI2O redox signal on the working surface without any prior pretreatment procedure. The formation of a reversible 1:1 CuIIO-amino acid complex on the Cun-SPE(100-nm) was proposed to play a key role in the reaction mechanism. Stable detection responses were obtained for all amino acids by flow injection analysis with detection limits (S/N = 3) that lie in the range of 24 nM-2.7 microM. Selected amino acids from six representative chemical natures were separated by HPLC and detected at the Cun-SPE(100-nm) with promising results.

Iron-enriched industrial waste cinder (CFe*) has been recycled for efficient and stable anchoring of Ru(CN)6(4-) to the formation of a hybrid ruthenium purple complex. The cinder/ruthenium purple hybrid-modified carbon paste electrode (designated as CPE/CFe*-RP) was worked out for hydrodynamic analysis of H2O2 at a low detecting potential of 0.0 V versus Ag/AgCl in pH 7 ammonium buffer solution. The highly active, selective, and stable electrocatalytic system with a function similar to peroxidase enzyme shows a linear calibration curve up to 0.8 mM H2O2 at a rotation rate of 3600 rpm with slope and detection limit (S/N = 3) of 0.11 microA/microM and 33 nM, respectively. Interference by direct electrochemical oxidation of easily oxidizable substances can be prevented as a result of the low detecting potential of the working system. A glucose biosensor was further constructed by coating with glucose oxidase and Tosflex on the CPE/CFe*-RP (denoted as CPE/CFe*-RP/GOx/Ts). The proposed CPE/CFe*-RP/GOx/Ts with a two-layer configuration, that is, enzyme and protecting layers, exhibits good operational performance in terms of response time, linearity, detection limit, and lifetime.

We report here an efficient photocatalytic amperometric sensor for the determination of dissolved oxygen (DO) in phosphate buffer solution using a disposable copper-plated screen-printed carbon electrode (CuSPE). The photoelectrochemical activity toward DO of the CuSPE was related to the formation of a p-type semiconductor Cu(I)2O. The solution pH and biased potential (E(bias)) were systematically optimized as pH 8 PBS and -0.7 V vs Ag/AgCl, respectively. Under optimized conditions, the calibration plot was linear in the range of 1-8 ppm with sensitivity and regression coefficient of 23.51 (microA cm2)(-1) ppm(-1) and 0.9982, respectively. The reproducibility of the system was good with seven successive measurements of DO yielding a RSD value of 1.87%. Real sample assays for groundwater and tap water were also consistent with those measured by a commercial DO meter. The principle used in DO measurement has an opportunity to extend into various research fields.

An artificial enzyme analogue of Nafion/lead-ruthenium oxide pyrochlore (Py) chemically modified electrode (NPyCME) is synthesized by in situ precipitation through blocking of Nafion’s hydrophilic zones. The catalytically active Py sites covered with a hydrophobic core of Nafion resemble an enzymatic structure. Moreover, the NPyCME obeys the Michaelis-Menten mechanism for the oxidation of many organic and biological molecules. This Account highlights aspects of the preparation, characterization, and application of the NPyCME.

Unusual electropolymerization of aniline to polyaniline (PANI) in a neutral pH solution has been successfully demonstrated using a multiwalled carbon nanotube (MWCNT) modified gold electrode (Au-MWCNT@PANIpH7). The modified electrode showed highly redox active surface confined peaks corresponding to the molecular transitions of leucoemeraldine-emeraldine and emeraldine-pernigraniline in pH 7 phosphate buffered solution (PBS), along with a low capacitance behavior, in contrast to the conventional acidic solution PANI systems. Control experiments in the absence of MWCNTs (i.e., Au/PANIpH7) and in an acidic medium, pH 2 (i.e., Au-MWCNT@PANIpH2), resulted in nil and poor redox features respectively. The physicochemical characterization of the MWCNT@PANIpH7 film by TEM, Raman spectroscopy, FTIR and UV-Vis revealed the presence of polaron type PANI structures on the MWCNT surface. More interestingly, MWCNT@PANIpH7 showed a highly selective electrocatalytic signal to ascorbic acid (AA) at a low oxidation potential, -15 mV vs. Ag/AgCl, without interference from nitrite, uric acid, dopamine, glucose, cysteine and citric acid in pH 7 PBS. Extended flow injection analysis yielded an excellent AA sensing response with a detection limit (signal-to-noise ratio = 3) of 42 nM, which is better than that of the conventional acid assisted MWCNT@PANIpH2 and MWCNT systems.

A disposable-type screen-printed non-single crystal silver electrode (AgSPE) surface has been demonstrated for the sensitive and selective quantification of lead in cosmetic hair-dye formulations u...