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A morphological and electroanalytical characterization of a glassy carbon electrode modified with multi-walled carbon nanotubes dispersed into cellulose acetate polymer matrix (GC/MWCNT/CA), was reported. The morphology of the modified electrode reveals a favorable distribution of the carbonaceous fibers interconnected within the cellulose acetate matrix, showing an improved active surface area. The electrode was tested as an sensing probe for the detection of some important catecholamines such as dopamine and epinephrine using cyclic volatmmetry and differential pulse voltammetry (DPV) in 50 mM H3PO4. Under DPV conditions, the detection limits of the investigated catecholamines are comprised between 1 μM and 10 μM. A reverse phase chromatographic technique (pH 3.5), coupled with the GC/MWCNT/CA amperometric sensor was optimized for the separation and quantification of the tested catecholamines. Under the optimized conditions, the investigated analytes, including an important urinary catecholamine metabolite such as the vanillylmandelic acid, were eluted and separated in about 10 min with good chromatographic efficiency and resolution. The effects of various common interferents on the analytical signal, were also evaluated. A solid phase extraction pre-concentration procedure accomplished with chromatography and electrochemical detection allows the possibility to lower the detection limits of the investigated molecules at level of 1–5 nM. Real samples of pharmaceutical vials and urine samples were successful analyzed using the proposed amperometric sensor in two different analytical contexts: DPV and amperometry after solid phase extraction procedure coupled with liquid chromatography.

A composite electrode material based on graphene oxide (GO) and polyvinyl alcohol (PVA) containing electrodeposited Ni-Co species was electrochemically characterized in alkaline medium (0.1 M NaOH). The well distinct Ia/Ic redox couple shifts to the cathodic potentials in presence of Co oxide species contained in the active deposit. The effect of the potential scan rates (ν) on the Ia/Ic redox couple was studied in the range comprised between 10 mV s−1 and 250 mV s−1. The plots of the log(peak current) vs log(ν) gave straight lines with slopes between 0.65 and 0.75, showing a diffusive character of the redox currents. Continuous potentiostatic charge/discharge process between 0.4 V and 0.1 V vs SCE were carried out in alkaline medium in order to ascertain the supercapacitor performance of the investigated GC/GO/PVA/Ni-Co electrode. The composite electrode shows significantly higher capacitance (3.1 × 10−4 F). Admitting the only Ni-Co oxide as active electrode material, a specific capacitance of about 2100 ± 200 F g−1, was evaluated. During the charge/discharge process in alkaline medium, the electrode system shows, after an initial physical stabilization, a good electrochemical stability ( sorbitol > glycerol > methanol. Flow injection analysis (FIA), performed under flowing 0.1 M NaOH solution and an applied constant potential of 0.5 V, show well-defined symmetrical and reproducible peaks in a wide range of concentration of investigated analytes.

The palladium species were deposited on the multi-walled carbon nanotubes dispersed in nafion membrane by pulsed electrodeposition technique. The resulting modified electrode was defined CNT-Pd. The Pd electrodeposition was carried out in 50 mM H 2 SO 4 solution containing 4.0 mM Pd(NO 3 ) 2 using a double pulse sequence of potentials: E 1 = −0.4 V vs SCE (t 1 = 0.03 s) and E 2 = 0.4 V vs SCE (t 2 = 3 s). SEM analysis showed a well-efficient distribution of Pd nanoparticles dispersed along the nanotubes randomly oriented in the nafion matrix. A surface loading of electrodeposited Pd species comprised between 2.0 nmol and 2.5 nmol was generally observed. The prepared electrode is useful to catalyze the electrooxidation of hydrazine and propranolol. The electroanalytical properties of the electrode were evaluated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Under optimized DPV conditions, the CNT-Pd electrode exhibits interesting analytical performance in terms of linear range of concentrations, low detection limits (i.e., 8 μM and 2 μM for hydrazine and propranolol, respectively) and good temporal stability of the responses (i.e., 4%–5%).

A study regarding the electrodeposition of nickel oxide particles on the activated multi-walled carbon nanotubes from 2 M NaOH solution containing Ni(NO3)2 and EDTA was carried out. The electrodeposition process was carried out using an optimized double-pulse sequence of potentials: E 1 = −0.2 V vs. SCE (t 1 = 0.3 s) and E 2 = 0.7 V vs. SCE (t 2 = 0.03 s). Spectroscopic XPS investigations and SEM analysis were used in order to characterize the surface and morphology of the studied modified electrode. Cyclic voltammetry and chronoamperometry were used in order to evaluate the electrochemical/amperometric performance of the GC/MWCNT-Ni electrode toward the oxidation of some aliphatic alcohols in strong alkaline medium.

An IrOx modified electrode was characterized and proposed as an amperometric sensor for the detection of semicarbazide using cyclic voltammetry, chronoamperometry and amperometry techniques. The modified electrode was characterized as sensing probe in both acid and alkaline medium toward the electrocatalytic oxidation and detection of semicarbazide. A liquid chromatography approach based on the strong cation exchange mode (LC-SCX column) was used in acid conditions for the separation and analysis of semicarbazide in a synthetic mixture. Operating under a constant applied potential of 1.1 V vs. Ag/AgCl and using HClO4 as carrier electrolyte, the limit of detection (LOD) is attested at level of 0.1 μM (i.e., 7.5 μg L−1), while an excellent precision and temporal stability of the amperometric signal, was observed. The linear ranges spanning over three order of magnitude of the detection limit with a correlation coefficients higher than 0.995.

A gas sensors based on a room temperature ionic liquid (RTIL) supported on paper is proposed as amperometric sniffer for monitoring volatile amines (VAs) released from fish samples, in order to gain indication of their state of turning spoiled. It was used as a paper electrochemical detector (PED) for a flow injection system in which controlled headspace volumes in equilibrium with ice-stored fish samples were directly injected. The performance of this RTIL-PED sensor was preliminarily tested on synthetic samples of trimethylamine (TMA), dimethylamine (DMA), methylamine (MA) and ammonia (i.e. the main species responsible for the typical flavor of spoiled fish), thus verifying that only TMA, DMA and MA can be detected because NH3 oxidation occurred beyond the solvent discharge. This notwithstanding, detection of the sole TMA, DMA and MA as a whole turned out to be well suited for the rapid assessment of fish spoilage, since during storage the release enhancement for these amines is largely predominant over that of NH3. Repeatable (8 % RSD) sharp peaks were detected for all amines above over a wide range (5–1000 nmol) and a detection limit of a little more than 3 nmol was inferred for a signal-to-noise ratio of 3. This approach was applied to the detection of VAs released from real fish samples (sardines), in parallel to the determination of their total volatile basic nitrogen (TVBN), which is a conventional indicator frequently adopted for the chemical quality assessment of fish. A substantially satisfactory agreement was found by comparing the data achieved by these two approaches.

The rhodium particles can be electrodeposited on a glassy carbon electrode, previously modified with multi-walled carbon nanotubes (MWCNTs), by voltage cycling between 0.4 V and–0.3 V vs. SCE (30 cycles) in 50 mM H2SO4 containing 4.0 mM RhCl3. This proposed modified electrode is useful to facilitate the electrocatalytic reduction of nitrate and nitrite ions in acid medium. The mechanism of the electrocatalytic reduction of nitrate and nitrite ions in the hydrogen region of potentials was critically considered using voltammetric and DC/pulsed amperometric detection techniques. The GC/MWCNT-Rh electrode shows interesting sensitivity and temporal reproducibility towards nitrite and nitrate reduction under constant and pulsed applied potentials, respectively.

Nickel oxide species, palladium metal and complex Ni–Pd particles were deposited on the glassy carbon electrode by pulsed electrochemical conditions from 0.5 M NaOH solution containing 5 mM gluconate ion, 0.5 mM Ni(NO 3 ) 2 and/or 2 mM Pd(NO 3 ) 2 . The electrodeposition process was performed using the following potentials and pulse durations: E 1 = −1.0 V and E 2 = +0.8 V vs. SCE, t 1 = 50 ms and t 2 = 50 ms for the relevant times of 600 s. The nickel oxide particles were deposited during the anodic pulse of potentials, while the palladium particles were deposited during the cathodic sequence of the potential pulses. The Ni–Pd system shows an acceptable character of electrochemical reversibility and a high affinity for oxygen adsorption. The XPS and SEM techniques were used in order to define the surface chemical composition and the actual morphology of the deposited material. An average surface chemical composition of Pd 0.5 Ni was established and the composite appears formed of well dispersed single globular particles having an average size comprised between 50 nm and 150 nm of diameter.

A composite material based on Polyvinyl alcohol (PVA) and graphene oxide (GO) was used as electrode substrate for the Ni-Co electrodeposition in neutral chloride bath containing 1.5 mM Ni(NO 3 ) 2 and 4.5 mM Co(NO 3 ) 2 . Ni-Co particles were cathodically deposited by voltage cycling between − 0.5 V and 0.2 V vs. SCE (35 cycles). Voltammetric data show clearly an inhibition phenomenon of nickel oxide deposition upon increasing [Co 2+ ] in the electroplating baths. Nevertheless, the presence of electrodeposited Co oxide species induces beneficial effects on the redox electrochemical behavior of the GC/PVA/GO/Ni-Co electrode in alkaline medium (0.1 M NaOH). The resulting electrode shows, a unique and reversible symmetrical cathanodic wave centered at about 0.3 V vs SCE. The SEM analysis shows the graphene oxide disposed as platelets in a agglomerate distribution randomly oriented within the PVA matrix. The electrodeposition process of Ni-Co species proceeds preferentially on the GO platelets surfaces. After the charge/discharge process in alkaline medium, the Ni-Co deposit shows a globular inhomogeneous distribution with an average diameter comprised between 50 nm and 300 nm. The XPS characterization of the electrodeposited Ni-Co catalyst reveals a surface chemical composition of about Ni 16 Co 84 , confirming an “anomalous” co-deposition process of the metals on the PVA/GO electrode substrate.

A simple electrochemical microprobe (EMP) is proposed for the detection of analytes in gaseous atmospheres. The EMP consists of two platinum fibres of 25 and 300 μm in diameter encased into a theta glass pipette to form an electrochemical cell in a two-electrode configuration. Ion conductivity between the two electrodes is ensured by a thin film of the room temperature ionic liquid (RTIL), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, which is applied onto the EMP tip surface by a simple dip-coating procedure. The ionic liquid-coated microprobe (RTIL-EMP) was preliminarily investigated by using ferrocene as an electroactive species to ascertain the mass transport properties of the analytes that influence the voltammetric responses as well as the stability and reproducibility of the RTIL-EMP in the gas phase. The performance of the RTIL-EMP to gas analysis was afterward evaluated by using oxygen as electroactive species. The RTIL-EMP was exposed to different synthetic O 2 /N 2 (v/v) mixtures and current responses were recorded as a function of O 2 concentration, using either cyclic voltammetry (CV) or chronoamperometry (CA). Regression analysis of the experimental current against % O 2 was linear over the range 0–100% with correlation coefficient and sensitivity of, respectively, 0.996 and 0.29 nA/(v/v) % O 2 in CV and 0.998 and 0.27 nA/(v/v) % O 2 in CA measurements. Long term stability, reproducibility of the RTIL-EMP recovery of the RTIL film layers to the initial conditions and effects of humidity on the current responses were investigated in detail.

Sulfonamides were oxidized at a polycrystalline gold electrode in neutral buffered phosphate medium at pH 7 and the electrochemical behavior was investigated using cyclic voltammetry technique. A liquid chromatography methodology based on the C18 reverse phase for the simultaneous separation of nine sulfamides, was studied and optimized. The amperometric detector using a polycrystalline gold substrate as working electrode and operating under pulsed amperometric detection mode (PAD) was tested for the determination of the selected molecules. Under optimal chromatographic and amperometric conditions, the limit of detection of the investigated sulfamides are comprised between 1 µM and 0.05 µM and the dynamic linear range spanned generally over three orders of magnitude. A liquid extraction procedure based on the use of acetonitrile solvent was tested and proposed for the quantitative extraction of sulfonamides from homogenized meat samples. The analytical method was successful tested for the determination of sulfonamides in homogenized meat-based baby foods with reproducibility and recovery levels ranged between 5.0 % and 7.6 %. and 86 %–106 %, respectively.

A study regarding the electrodeposition of Co oxides from alkaline medium containing 12 mM gluconate ligand and 12 mM Co2+ on glassy carbon, Au, Pt, Ni, Ti and ITO electrode substrate was carried out through cyclic voltammetry technique. Films of cobalt oxides were deposited either anodically by voltage cycling (100 mV s−1) between −0.3 and 0.6 V (SCE) or by potentiostatic conditions at potential comprised between 0.2 and 0.6 V for a fixed time of deposition. Analysis of the voltammetric experimental data clearly showed that the rate of cobalt oxide electrodeposition process decreases in the order Au > Pt > GC, Ni > Ti, ITO and the massive cobalt electrodeposition does not proceed to an appreciable extent until potentials of 0.3–0.4 V (SCE) is reached. The effect of the scan rate on the peak potential, peak current, and peak-to-peak separation of the deposited cobalt oxide films was studied, and some substantial differences in terms of electrochemical behaviour in relation at the specific substrate electrode were observed and critically discussed.

Cobalt oxyhydroxide modified glassy carbon electrodes (GC/Co) prepared by anodic electrodepostion in alkaline solution containing gluconate ions as ligand species have been characterized and proposed as sensing probes for the detection of hydrazine compounds. Under cyclic voltammetry and chronoamperometric conditions, the electrooxidation processes of hydrazines on the GC/Co are severely attenuated indicating strong and irreversible adsorption of the analyte on the electrode surface with subsequent formation of stable films with fouling effects on the catalytic sites. On the contrary, under flowing conditions the hydrazine compounds show well-defined and reproducible peaks with good analytical performance. Flow injection analysis (FIA) carried out at constant applied potential of 0.3 V vs. Ag/AgCl (4 M KCl) and using a flowing stream of 0.1 M NaOH solution containing 50 µM Co2L22− as “on-line” modifier, shows limits of detection (LODs) comprised between 0.5 µM for hydrazine and 2 µM for 1,2-dimethyhydrazine. Regression analysis, shows linear ranges spanning over about three orders of magnitude above the detection limits with coefficients of correlation better than 0.96.

In this study an electrodeposition procedure of cobalt oxides operating under anodic condition and directly from 0.5 M NaOH solutions containing 12 mM gluconate and 12 mM CoCl2 was defined for the modification of glassy carbon surface electrode. Different experimental approaches based on cyclic voltammetry, steady-state potentiostatic technique, chronoamperometry and scanning electron microscopy were used to characterize the deposited cobalt oxide films and to evaluate the kinetics and mechanism of electrodeposition. Some aliphatic aldehydes were tested as compound model in order to evaluate the electroanalytical properties of the electrodeposited cobalt film as active redox material for amperometric applications in strong alkaline aqueous solutions. Interesting results in terms of surface electrode modification “in situ” of glassy carbon substrate with cobalt oxides were obtained and critically discussed.

A pulsed electrochemical method was used for the preparation of silver deposit onto glassy carbon surfaces from an alkaline medium containing ammonia ligand. The morphology of the silver deposit, obtained under pulsed and cyclic conditions was examined and compared using the scanning electron microscopy (SEM) technique. From the experimental evidences, it can be inferred that pulsed method induces a favourable dendritic growth of silver particles, while deposited films obtained under cyclic voltammetry appear formed of globular particles with well regular and defined surface geometry. The electroanalytical performance of the deposited silver, towards the electroreduction of NO 3 − , BrO 3 − and ClO 2 − ions, using cyclic voltammetry and chronoamperometry technique, was evaluated. Interesting analytical results, in terms of sensitivity and temporal reproducibility, in alkaline medium and under constant applied potentials (i.e., −1.45 and −0.6 V vs. SCE), were obtained.

A liquid chromatography based on the reverse phase separation and a solid phase extraction (SPE) procedure using a phenyl-silica sorbent for the simultaneous separation and extraction/preconcentration of six tetracyclines was studied and optimized. An amperometric detector using a polycrystalline gold electrode operating under both DC and IPAD conditions was tested for the determination of the selected tetracyclines. Under optimal SPE and chromatographic conditions, the limit of detection of the investigated tetracyclines comprised between 50 nM (25 microg L(-1)) and 75 nM (37 microg L(-1)), and the dynamic linear range spanned generally over 3 orders of magnitude, when the electrochemical detector was used under DC conditions at a constant applied potential of 1.6 V vs Ag/AgCl. The analytical method was successfully tested for the determination of tetracyclines in milk samples ((UHT low-fat, fresh pasteurized, and powdered milk) with reproducibility and recovery levels ranged between 3.1%-5.6% and 70%-118%, respectively.

Palladium film can be deposited on gold polycrystalline electrodes, from a deoxygenated alkaline solution containing 50 mM NaOH plus 0.5 mM K 2 Pd(CN) 4 . A multipulse sequence of potentials of equal amplitude and duration was used for the palladium deposition process. In particular, an optimized waveform of potentials of E 1 = 1.0 V vs. SCE and E 2 = −1.0 V vs. SCE for the relevant pulse duration of t 1 = 0.05 s and t 2 = 0.05 s, for 30 s, was used. Cyclic voltammetry and scanning electron microscopy (SEM) were employed to characterize the gold–palladium modified electrode (Au–Pd) towards the electrooxidation of aliphatic alcohols in alkaline solutions. The voltammetric study suggests that the kinetics involved in the alcohol electrooxidation at the Pd–Au electrode are sensibly higher than those observed on the bare Pd and Au electrodes. In addition, the most interesting aspect of the electrooxidation of aliphatic alcohols at the Au–Pd electrode was that as the number of methylene groups on the homologous series of aliphatic alcohols increased, the molar response also increased. Under pulsed chronoamerometric conditions (PCC), using an optimized triple pulse waveform of potentials the modified electrode exhibits interesting catalytic currents without any apparent poisoning effects during the oxidation of aliphatic alcohols.

Palladium species can be immobilized on a glassy carbon electrode by voltage cycling between 0.0 and −0.4 V versus SCE in solutions containing 0.5 mM Na2PdCl6 in order to facilitate the electrocatalytic reduction of chlorophenoxycarboxylic acids in solutions buffered at pH 7. Cyclic voltammetry, measurements at the rotating disc electrode (RDE) and chronoamperometric techniques were used in order to investigate the electrochemical behaviour of the modified electrodes (GC/Pd) towards the catalytic reduction of chlorophenoxycarboxylic acids. A reaction mechanism is proposed and discussed. A probable scheme for the electroreduction of chlorophenoxycarboxylic species in neutral medium involves a simultaneous and competitive adsorption of the organic molecules and hydrogen atoms on the catalytic sites, followed by an irreversible hydrodechlorination reaction. 2,4-Chlorophenoxyacetic acid can be dehalogenated to a chlorine-free product in neutral aqueous solutions at relatively low cathodic polarizations and at ambient temperature using a GC/Pd electrode.

A gold polycrystalline electrode modified with rhodium species was characterized by electrochemical and XPS (X-ray photoelectron spectroscopy) techniques in moderately alkaline medium. The Au/Rh electrodes were prepared utilizing a spontaneous deposition process (SDP) of rhodium adlayer on the gold surface. In particular, rhodium deposition was obtained in non-deaerated 50 mM HClO 4 solution containing 10 mM RhCl 3 at open circuit for a given time. The modified gold electrode with adsorbed rhodium species (Au/Rh) exhibit higher electrochemical activity for the oxygen evolution reaction. The effects on the electrochemical activity of the Au/Rh electrode such as: rhodium coverage, pH, electrolyte composition and applied potentials were critically evaluated and discussed. An optimized pulsed chronoamperometric detection technique for the analytical determination of several mono- and di-protic organic acids such as acetic, tartaric, oxalic, malic, etc., was successfully proposed. An average film composition of Au 93±1 Rh 7±1 was evaluated by XPS technique. The film composition remains unchanged after various electrode treatments such as cycling of potentials and/or polarization conditions for long times in alkaline medium. Thus, the adsorbed rhodium oxide particles show a good chemical and mechanical stability despite the conditions of electrochemical treatment of the electrode surface.

The electrochemical and amperometric behavior of a gold electrode was investigated towards the oxidation of several common phenolic acids in neutral phosphate solutions. Au electrodes show an appreciable stability and reproducibility of the amperometric signals by using a constant applied potential of 1.0 V vs. Ag/AgCl. Separations of selected phenolic acids using a reverse phase C18 analytical column with a mobile phase containing 10 mM NaH2PO4 plus 10 mM Na2HPO4 (pH 7) and methanol as organic modifier, are achieved isocratically in less than 30 min. The detection limits at the level of nmol/L and linear ranges of four-five orders of magnitude are generally achieved. The proposed chromatographic strategy coupled with the electrochemical detection at the Au electrode was successful tested for the quantitative determination of phenolic acids in beer, red wine and brandy with good sensitivity and recovery.

Palladium–bismuth films supported on glassy carbon substrates were prepared by cathodic electrodeposition of palladium ad subsequent adsorption of bismuth species on the electrode surface. A mechanism regarding the irreversible adorption process of bismuth species on the palladium surface, was described. The resulting active film was characterized, and in particular, the electrooxidation of some aliphatic aldehydes was investigated in moderately alkaline solutions. The bismuth adlayer increases the overall rate of the oxidative processes through a combination of a third body mechanism and a true catalyst. The oxidation currents of propionaldehyde, evaluated in cyclic voltammetry increased linearly on increasing analyte concentration up to 8 mM. Under chronoamperometric conditions at the constant applied potential of −0.2 V versus SCE, the resulting calibration plot for propionaldehyde analysis was linear over the range of 1.5–8 mM with a correlation coefficient better than 0.97. Throughout the XPS investigation Pd 3d and Bi 4f detailed regions an average chemical composition of the surface composite film of Pd 96±2 Bi 4±2 was evaluated.

Optimal conditions for Pd and Sn co-deposition were achieved by voltage cycling between 0.2 and −0.7 V vs. SCE in deaerated solution containing 0.5 mM Na2PdCl6, 0.5 mM SnCl2 and 25 mM HCl. Cyclic voltammetry and chronoamperometric techniques were used to investigate the electrochemical behaviour of the electrodeposited binary film toward the electrochemical reduction of nitrate species in slightly acid solutions. The relevant reduction mechanism was critically discussed. The resulting calibration plots for nitrate analysis performed under voltammetric conditions and in 50 mM H2SO4 solution are linear over the range 1.0–12 mM with correlation coefficients better than 0.984. The X-ray photoelectron spectroscopy technique (XPS) was used in order to evaluate the chemical composition of the binary electrodeposited film. Electrodeposited Pd30Sn70 films, independently of the electrochemical treatment, are composed of 50–60% of Sn metal and 40–50% of SnO of the total tin species, while the palladium species are composed by 60–70% of Pd and 30–40% of palladium oxides (i.e., PdOads and PdO).

The electrochemical behaviour of the polycrystalline platinum electrode towards the oxidation/reduction of short-chain unsaturated aliphatic molecules such as acrylamide and acrylic acid was investigated in acidic solutions. Analytes were separated by reverse phase liquid chromatographic and quantified using a pulsed amperometric detection. A new two-step waveform, is introduced for detection of acrylamide and acrylic acid. Detection limits (LOD) of 20 nM (1. 4 microg/kg) and 45 nM (3.2 microg/kg) were determined in water solutions containing acrylamide and acrylic acid, respectively. Compared to the classical three-step waveform, the proposed two-step waveform shows favourable analytical performance in terms of LOD, linear range, precision and improved long-term reproducibility. The proposed analytical method combined with clean-up procedure accomplished by Carrez clearing reagent and subsequent extraction with a strong cation exchanger cartridges (SPE), was successfully used for the quantification of low concentrations of acrylamide in foodstuffs such as coffee and potato fries.

Cyclic voltammetry was used to investigate the electrochemical behaviour of the tungsten oxide films toward the electroreduction of BrO 3 − , ClO 2 − and NO 2 − ions in acidic medium. The effects of the temperature, scan rate, pH, chemical composition of the electrolytic solutions, were investigated and the reduction mechanism was critically discussed. The reduction currents, evaluated in cyclic voltammetry and measured at −0.250 V versus SCE, increased linearly on increasing analyte concentration up to 20, 55 and 45 mM for nitrite, chlorite and bromate ions, respectively. The detection limits, evaluated in cyclic voltammetry, were 0.1, 0.4 and 0.7 mM for BrO 3 − , ClO 2 − and NO 2 − , respectively. The tungsten oxide film was successfully characterized as an amperometric sensor for the analytical determination of BrO 3 − , ClO 2 − and NO 2 − ions in flowing stream. Operating under constant applied potential of −0.3 V versus Ag/AgCl the good reproducibility of the peak height and background current level during consecutive injections, indicates the absence of fouling effects and the potential applicability of the amperometric sensor for the routine analytical determination of the investigated inorganic ions. Considering the low values of the background currents (ca. 1.1 ± 0.1 μA) obtained in acidic and not deoxygenated carrier electrolyte, the tungsten sensing electrode seems to compete favourably with other common sensors for the amperometric determination of electroactive molecules under cathodic conditions. The X-ray photoelectron spectroscopy technique (XPS) was used in order to evaluate the chemical composition of the tungsten film upon electrochemical treatment in 0.1 M H 2 SO 4 solution. Independently of the electrochemical treatment in acid solution, the tungsten surface electrode is generally composed by 50–60% of W 0 , 35–40% of W 6+ and traces of W 2+ oxide species.

The electrochemical behaviour of the copper–thallium composite film has been investigated in 10 mM NaOH solutions towards the electroreduction of nitrate and nitrite ions in the range of potentials between 0.0 and −1.4 V vs. SCE. The Cu45Tl55 binary films exhibited a higher electrocatalytic activity for the reduction of NO3− and NO2− than pure copper and thallium electrodeposited films. The presence of thallium species in the composite film causes a marked increase of the roughness factor with subsequent increase of the catalytic response due to the nitrate and nitrite reduction. Alternatively, thallium particles act as promoters of NO3− and NO2− adsorption on the electrode surface with their subsequent accumulation on the surface catalytic centres and increase of the cathodic currents. Under pulsed chronoamperometric detection (PCD) using a selected waveform of potentials of 0.0 V (Eads) for 200 ms (tads) and −1.3 V (Edet) for 400 ms (tdet), the Cu45Tl55 composite electrode exhibits interesting cathodic currents upon nitrate and nitrite addition. The detection limits (S/N=2), evaluated in PCD conditions for nitrate and nitrite ions were 190 and 250 μM, respectively.

Cyclic voltammetry and chronoamperometry have been employed for the preparation and characterization of noble metal electrode substrates modified with bismuth adlayers. The influence of bismuth ad-atoms on the electrocatalytic activity of the resulting platinum and gold modified electrode was investigated toward the electrooxidation of several sugar acid molecules in moderately alkaline medium. A direct comparative study regarding the catalytic activity between platinum and gold electrodes has been carried out in order to obtain useful information on the electrooxidation mechanism of sugar acids. It is found that different pre-adsorption processes of analyte on the platinum and gold electrodes were involved giving rise to different adsorption states in the oxide region and double region of potentials, respectively. The bismuth adsorbed species acts as a true catalyst on the direct electrooxidation pathway, providing the oxygen necessary for the oxidation of organic molecules adsorbed on the PtO x or Au sites in the oxide and double region, respectively.

An isocratic chromatographic separation with amperometric detection of underivatized amino acids at a copper oxyhydroxide modified glassy carbon electrode is described. A simple and sensitive quantitation procedure of amino acids without the need of tedious and time-consuming derivatization step was achieved by coupling anion-exchange chromatography with electrochemical detection. The effects of hydroxide, nitrate and acetonitrile concentration in the mobile phase on the capacity factors and peak resolution was evaluated. Under the optimized isocratic chromatographic conditions (i.e. 60 mM NaOH) and under constant applied potentials (i.e. 0.55 V versus Ag/AgCl) the detection limit ranged between 4 and 24 pmol injected and the linear dynamic range spanned generally over three or four order of magnitude for all investigated amino acid compounds. Direct determination of several common free amino acids in beer and milk samples were performed.

Glassy carbon electrode substrates coated with thin films of cobalt oxyhydroxide were investigated in moderately alkaline medium by cyclic voltammetry. The cobalt oxide formation process was accomplished in alkaline solution (30 mM NaOH) containing millimolar concentrations of CoCl 2 and ligand species such as sodium citrate. The cobalt oxide/hydroxide films were obtained either by voltage cycling between 0.4 and 1.1 V versus SCE or under potentiostatic conditions at moderate positive potentials (i.e. 0.5 V). The resulting electrodeposited film was characterized electrochemically in alkaline solutions by cyclic voltammetry and, independently of the electrodeposition procedure adopted, reveals three well-defined sets of redox waves related to the Co(OH) 2 /Co 2 O 3 , Co 2 O 3 /CoOOH and CoOOH/CoO 2 electrochemical transitions. The charge/discharge processes and the oxygen evolution reaction during continuous potential cycling were severely inhibited in the presence of increasing concentrations of electroinactive electrolytes (i.e. NaNO 3 , K 2 SO 4 , Na 3 PO 4 , etc.). The electrochemical behaviour of the electrodeposited cobalt oxide/hydroxide film in alkaline solution and in the presence of various organic molecules was also investigated.

An electrochemical procedure of anodic deposition of cobalt oxyhydroxide film on a glassy carbon substrate in an alkaline medium (i.e. pH 11.6) is described. The electrodeposited film was obtained either by voltage cycling or by potentiostatic conditions using non-deaerated 0.1 M Na2CO3 solutions containing 40 mM tartrate ions and 4 mM CoCl2. The effects on the film formation and growth, such as tartrate–cobalt ratio, pH, applied potential, etc. were widely evaluated. The electrodeposition process, under anodic conditions and moderately alkaline solutions, most likely involves a redox transition Co(II)→Co(III)/Co(IV) with destruction of the tartrate complex and formation of insoluble oxide/hydroxide cobalt species on the glassy carbon surface. The resulting cobalt oxyhydroxide films were characterised by cyclic voltammetry (CV) in 0.1 M NaOH solutions and by scanning electron microscopy (SEM) analysis after different strategies of preparation and various electrochemical treatments. The electrochemical activity of the deposited films was checked using various organic molecules as model compounds.

Chemically modified electrodes obtained by direct interaction between gold substrate and tetracyanonickelate(II) ions in alkaline medium were characterized by cyclic voltammetry toward the electrooxidation of carbohydrates. Satisfactory performance with respect to catalytic stability, background current stability and lowering of detection limit was obtained for the analysis of ten oligosaccharides contained in a synthetic sample by anion-exchange chromatography in alkaline solutions. Under constant applied potential of 0.55 V (vs. Ag/AgCl), the detection limits (S/N=3) for all investigated compounds ranged between 3 and 6 pmol injected for melezitose and turanose, respectively. The dynamic linear ranges spanned generally three orders of magnitude above the limit of detection. The effects of the concentration of tetracyanonickelate(II) ion on the catalytic activity, amperometric stability and chromatographic separations were examined.

A simple, sensitive and rapid method is described for determining histamine in alkaline media by anion-exchange chromatography with amperometric detection at a copper-based modified glassy carbon electrode. The influence of copper loading, applied potential and flow rate on the amperometric signal was evaluated. Under optimal chromatographic conditions, the detection limit for histamine (S/N=3) was 0.1 μM (corresponding to 5 pmol injected by a 50-μl sample loop). The linear range spanned from 5 to 500 μM (correlation coefficient=0.998). The proposed method allows a rapid and convenient quantitation of histamine in real matrices, such as canned tuna and red wine, without time-consuming clean-up or derivatisation procedures.

A novel procedure of anodic electrodeposition of copper oxides and hydroxides on glassy carbon and noble metals electrodes in an alkaline medium is described. The deposited films have been investigated by electrochemical and by X-ray photoelectron spectroscopy (XPS) techniques. The copper films are deposited on the electrode surface as Cu(OH)2 and CuO after the dissociation of the Cu(CN)n1−n complex caused probably by the formation of CuIII species at relatively high applied potentials (i.e. 0.5 V). The resulting active copper films, independently of the electrochemical procedure adopted (i.e. potentiostatic or potentiodynamic conditions), appear to be uniform, smooth and with a good degree of adhesion on the electrode surface The electrocatalytic properties of the copper deposited films were investigated in an alkaline medium for the electrooxidation of several classes of organic compounds.

A nickel-based composite electrode obtained by anodic electrodeposition of nickel (III) oxyhydroxide film on the gold electrode substrate was characterized as an amperometric sensor and successfully applied to the determination of underivatised amino acids in flow-through systems. The electrodeposition of nickel oxyhydroxide films was obtained by cycling a gold electrode between 0.0 V and +1.0 V vs. a saturated calomel electrode in a 80 μM Ni2+ solution buffered at pH 10 with NaHCO3/Na2CO3. The resulting Au–Ni composite electrode exhibits good stability in alkaline medium and can be used as an amperometric sensor of underivatised amino acids at a fixed applied potential (+0.55 V vs. Ag/AgCl). The detection limits (S/N=3) for all investigated compounds ranged between 5 and 30 pmol injected, while the linear ranges spanned over two or three orders of magnitude. The contents of several free amino acids in two sample cheeses from different brands were evaluated by calibration graphs.

Dissolved sulfide ions are separated and detected by using ion chromatography (IC) and electrochemical detection with a glassy carbon electrode modified by electrochemical deposition of palladium particles. The influence of various experimental factors such as pH, loading of palladium, applied potential and flow rate of mobile phase is evaluated. The effect of some common organic and inorganic compounds on the amperometric signal is also evaluated. Under optimal chromatographic conditions, the detection limit for sulfide (S/N = 3) was 0.3 mu M (15 pmol injected) and the calibration plot was linear for 0.5-350 mu M sulfide (r=0.9964, n=16). The separation and detection of sulfides in human blood serum is presented as an example of an application to real specimens. (C) 2000 Elsevier Science B.V. All rights reserved.

A novel chemically modified electrode prepared by anodic electrodeposition of cobalt (III) film on the gold electrode substrate (Au-Co) was characterised by cyclic voltammetry and XPS techniques in both neutral and alkaline medium. Cobalt oxyhydroxide film was deposited by cycling the potential between 0.0 and 1.1 V versus SCE in 0.1 M sodium acetate solutions containing 10 mM CoCl2. The electrocatalytic properties of the Au-Co electrode were investigated in alkaline medium using glucose as a model compound. A comparative XPS study of bare gold, bare cobalt and Au-Co electrodes after electrochemical treatment in neutral and alkaline solutions has been carried out. A detailed XPS analysis of the Au4f(7.2), Co2p(3.2), O1s and C1s regions was performed to check the chemical composition of the Au-Co electrode upon electrochemical treatments. Film deposition is attributed to growth of conducting and compact CoOOH oxyhydroxide with significant insertion of carbonyl groups within the electrodeposited layer. The prolonged electrochemical treatment in alkaline medium produces a good stabilization of the Co-III oxyhydroxide film, with a dominant O1s feature at about 532.4 eV of BE corresponding to a non-stoichiometric surface oxygen. The absence of CoO species proves good conducting properties of the cobalt film and the absence of any passivation effects on the catalytic performance. (C) 1999 Elsevier Science S.A. All rights reserved.

The influence of Ba2+, Ca2+ and Sr2+ ions on the anion-exchange chromatographic separation of some carboxylated sugar acids such as d -gluconic acid, N-acetylneuraminic acid, muramic acid and d -galacturonic, d -mannuronic and d -glucuronic acids was investigated. The chromatographic technique was coupled with pulsed amperometric detection using gold as a working electrode. Since acidic carbohydrates are strongly retained on the anion-exchange column, acetate and nitrate as counterions were used to regulate retention within 30 min. The addition of alkaline-earth metal ions at a millimolar concentration to the alkaline eluents does impart a noticeable decrease in the retention, especially for N-acetylneuraminic and uronic acids. Complexation of these compounds with free divalent metal ions presumably occurs in the alkaline eluent. The extent of decreased retention is related to each divalent metal ion, and a good correlation was found between the retention modulus (η=k′/ko′) and the stability constant of each sugar–metal ion complex. As expected, calcium ion induced a slightly greater retention compared to strontium and barium ions, and this is consistent with the fact that alduronate–calcium complexes are relatively more stable (η

The electrocatalytic oxidation of oxalic acid in 0.1 M HClO4 solutions at a palladium-based chemically modified glassy carbon electrode was investigated by cyclic voltammetry. The effects of applied potential, scan rate, pH, palladium loading, Pd(II) bulk concentration, rotation speed of the electrode on the electrooxidation process of oxalic acid have been evaluated. Two independent electrooxidation processes, which involves different palladium species and intermediates of reaction are taken into account to explain the electrochemical behavior of the palladium-based glassy carbon modified electrode towards the oxidation of oxalic acid in acidic medium.

Cyclic voltammetry, flow injection analysis and liquid chromatography experiments were performed to characterise a palladium-modified glassy carbon electrode as an amperometric sensor for the determination of oxalic acid in perchloric acid solutions. The effects of several common interferents on the amperometric signal were also evaluated. The electrode stability, precision, limit of detection and linear range were evaluated at a constant applied potential of 1.1 V vs. Ag/AgCl. Calibration plots, obtained using liquid chromatography, were linear from 0.2 μ M to 1.2 m M ( r 2 =0.9986) and the detection limit was 0.15 μ M for a 50-μl injection. An example of analytical application, which includes the chromatographic separation and detection of oxalic acid in human urine, is given.

A chemically modified electrode composed of mixed hydroxide and oxyhydroxide nickel film (6-8 nmol cm(-2)) on the gold substrate (Au \ Ni) was characterized by cyclic voltammetry and XPS techniques. The gold substrate electrodes were firstly electrochemically conditioned in 0.2 M NaOH by cycling the potential between -0.25 and 0.6 V versus SCE, then modified by cathodic electrodeposition of nickel hydroxide films. These nickel films were obtained either by voltage cycling (50 mV s(-1)) between 0.0 and -0.5 V (SCE) or at constant potential of -0.3 or -0.5 V using non-deaerated 50 mM Ni(NO3)(2) solutions. X-ray photoelectron spectroscopy (XPS) characterisation and voltammetric behaviour of Au \ Ni electrodes in alkaline solutions are described. Continuous electrochemical cycling of the Au \ Ni electrodes induces significant changes of the nickel films in terms of crystallographic structures and chemical composition. Combination of XPS and electrochemical methodologies have demonstrated the ability to follow the morphological and chemical changes in alkaline solutions upon cycling potentials. Angular-dependent XPS measurements have demonstrated that electrochemical treatment induces the formation of a uniform film layer with the following chemical distribution: Au \ Ni(OH)(2) \ NiOOH. The electrocatalytic activity of the Au \ Ni electrodes is investigated in alkaline medium using glucose as a model compound. The favourable combination of active species such as gold and nickel leads to a sensing electrode with strong catalytic activity over a wide range of applied potentials. (C) 1999 Elsevier Science S.A. All rights reserved.

The voltammetric behavior of a glassy carbon electrode modified with multiwalled carbon nanotubes (MWCNTs) and Au particles was studied in alkaline medium towards the electrooxidation of some carbohydrates used as model compounds. The influence of carbohydrate concentration and scan rate on peak potentials, peak currents, etc., observed at the modified electrode was evaluated and critically discussed. The Au particles dispersed into multiwalled carbon nanotubes structures showed favorable electrocatalytic and analytical properties towards the electrooxidation of xylose and glucose molecules. Atomic force microscopy performed on the resulting modified electrode showed a well-efficient 3D distribution of Au active particles having sharp-edged and elongated grains along bundles of the MWCNTs. The three-dimensional MWCNT-Au composite structure of the catalyst act as a promoter to enhance the diffusive character of recorded currents and probably also increases the rate of the heterogeneous electron transfer of the electrooxidation process considered.

A bimetallic electrode composed of copper microparticles dispersed onto a gold surface (Au/Cu) has been investigated as an amperometric sensor using glucose as a model compound. Such a sensing electrode has been prepared by electrochemical deposition of Cu-0 from 50 mM CU2+ and subsequent potential cycling in an alkaline medium. The morphology of the copper deposit has been examined by scanning electron microscopy. The effects of copper loading, scan rate, hydroxide concentration, and applied potential on the electrocatalytic oxidation of glucose have been also investigated. Long-term electrode stability, background current, sensitivity, and linear range of the Au/Cu electrode have been assessed for constant-potential amperometric detection (DC) at +0.550 and +0.350 V, and in pulsed-potential amperometric detection (PAD). When used as an amperometric sensor in the DC mode at an applied potential of +0.350 V, the bimetallic electrode yields a detection limit of 0.8 pmol glucose (S/N=3) with a linear dynamic range of four orders of magnitude. Comparable results have been obtained when the bimetallic sensing electrode was used in the DC mode at +0.550 V and in the PAD mode. Good mechanical stability under forced flow hydrodynamic conditions was also found upon changing the detection mode from DC to PAD and vice versa, making the multifunctional amperometric sensor very attractive for analytical applications in flowing streams. (C) 1997 Elsevier Science B.V.

An anion-exchange column coupled with an amperometric sensor was used for the quantitative analysis of alditols and simple sugars. The sensing electrode is composed of cuprous oxide dispersed in a graphite powder–polyethylene composite matrix. The resulting Cu2O–carbon composite electrode is stable in alkaline media and possesses good sensitivity, wide linear dynamic ranges and low detection limits for alditols, mono- and disaccharides. Alditols and carbohydrates are weakly ionizable compounds, so an anion-exchange column was employed for their chromatographic separation with an alkaline eluent. The separation problems due to the presence of low but uncontrolled amounts of carbonate in the alkaline mobile phase have been largely solved by the addition of Ca2+ or Ba2+ at a millimolar level and the consequent formation of carbonate insoluble salts. Using this strategy, the alkaline eluent provides improved separations without compromising the column's lifetime, electrode performance and chromatographic system. Under the optimal operating conditions, the detection limits of d -sorbitol, d -mannitol and d -glucose were 50, 40 and 80 pmol, respectively, with a linear concentration range up to 5 mM. Examples of applications, which include the separation and detection of d -sorbitol, d -mannitol and common sugars present in food samples, are illustrated.

Cyclic voltammetry was used to investigate the electrochemical behavior of nitrite at a platinum-modified glassy carbon electrode (Pt-CME) in phosphate buffer (pH 4.5). Experiments in flow injection analysis and ion-chromatography (IC) were performed to characterize the electrode as an amperometric sensor for the determination of nitrite ions. 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 a constant applied potential of 1.1 V. Calibration plots were linear from 0.03 μM to 0.5 mM with a slope of about 21 μA/mM and a correlation coefficient of 0.9987. The limit of detection (LOD) was 15 nM (0.7 ppb) in a 100 μL injection. The electrode response was sufficiently stable: over 6 h of operating time a 2.8% signal loss was observed. The determination of nitrite in milk and pear juices was achieved by IC and the relevant results were compared with those obtained with a standard spectrophotometric method.

A chemically modified electrode composed of copper microparticles dispersed into a polyaniline (PANI) film was investigated as an amperometric sensor of scarcely electroactive compounds possessing -OH and -NH2 groups. Glassy carbon was used as an electrode material and modified firstly by a PANI film, then allowed to stand in contact with a solution of copper ions, and finally, the electroreduction was done at −0.3 V. The electrochemical behaviour of the resulting modified electrode in alkaline medium was examined by cyclic voltammetry and flow-injection amperometry. Using some representative compounds, the effect of copper loading and pH on the electrode response was investigated. Constant-potential amperometric detection was applied in conjunction with anion-exchange chromatographic (AEC) separations of amino acids and carbohydrates. At an applied potential of 0.55 V vs. AgAgCl, the detection limits (SN = 3) for all analytes investigated ranged 5–15 pmol, and the linear dynamic range was three–four orders of magnitude above the detection limits. The resulting modified electrode was found to retain 95% of its initial response in flowing streams for 3 h of operating time.

A platinum-based chemically modified glassy carbon electrode (Pt-CME) was characterized in acidic medium by X-ray photoelectron spectroscopy, scanning electron microscopy and electrochemical techniques. A uniform distribution of platinum microparticles of different form and size (hexagonal, grain-like and globular) was present on the surface of glassy carbon. The chemical species present on the electrode surface changed upon polarization. At higher potential values (1.5 V) species such Pt(OH)2, Pt(OH)ads and Pt(OH)4 formed at lower potential values were transformed into PtO, PtOads and PtO2 respectively. A few aspects of the electrooxidation of ethanol in acidic medium were investigated on the Pt-CME described.

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.

The electrocatalytic oxidation of sulfite in an acidic medium at a platinum-based, chemically modified glassy carbon electrode (Pt-CME) was investigated. The electrode was characterized by voltammetry and flow injection, and applied to the determination of total and free sulfite by ion-exclusion chromatography with direct current and pulsed amperometric detection. The described electrode showed a promising combination of background current stability, catalytic activity detection limit (0.25 and 0.50 μg l −1 by direct current and pulsed amperometric detection, respectively) and reproducibility. Examples of determination of free and total sulfite present in fruit juice were achieved by ion chromatography with electrochemical detection. The detector can be used for the analysis of real samples, avoiding tedious or complex pretreatment, with an acceptable level of selectivity and accuracy.

A platinum-modified glassy carbon electrode was investigated as an amperometric sensor for the determination of alcoholic species in acidic medium. The described electrode was tested in liquid chromatography and flow-injection analysis by pulsed amperometric detection. It showed a promising combination among catalytic activity, detection limits and reproducibility for the determination of alcoholic species. The electrode response was stable; over 8 h a signal loss of less than 5% was observed. Linear responses at low concentrations yielded detection limits in the 0.6–1.8 μg ml−1 ranges for the various aliphatic alcohols. Typical relative standard deviations were comprised between 1.2% and 3.8% for all mono-and polyhydric compounds investigated. Linear plots of 1 I p and 1 C indicated Langmuir-type adsorption of analytes on the electrode surface. The Pt chemically modified electrode showed a few important differences with the bulk platinum electrode: i.e., a greater extension of linear range for relatively high concentrations and different trend of sensitivity towards the catalytic oxidation of mono-and polyhydric species.

Sugars and alditols undergo an electrocatalytic oxidation in alkaline solution at cobalt-oxide-based glassy carbon (Co/GC) electrodes. The catalytic deposit was investigated by cyclic voltammetry and scanning electron microscopy (SEM). It is pointed out that, at relatively low coverage of cobalt, two main redox processes, CoII CoIII and CoIII CoIV, are observed in 0.2 M NaOH. The redox behavior of the Co/GC electrode is strongly dependent on hydroxide ion concentration, and no electrocatalytic activity is observed at pH lower than 11.5. Under voltammetric conditions the modified electrode exhibits a non-Nernstian potential/pH shift (−88 ± 3 mV per pH unit). A reasonable explanation of the E/pH behavior in alkaline solution is given and an oxidation mechanism of CoII to CoIII is proposed in terms of hydrous cobalt oxides. No detrimental effects on the electrocatalytic oxidation of polyhydric compounds are observed in the presence of high acetonitrile concentrations (up to 40%). Inspection by SEM of the cobalt-based deposit evidenced the presence of grain-like microcrystallites on the glassy carbon surface.

After a suitable cleaning treatment, high modulus, unsized, polyacrylonitrile-derived carbon fibres were surface-treated by negative d.c. corona discharges under a flow of various nitrogen/oxygen mixtures at ambient pressure and temperature. The surface composition and morphology of the fibres, characterized before and after the treatment by X-ray photoelectron spectroscopy, X-ray excited Auger spectroscopy and scanning electron microscopy, were influenced by several experimental parameters (applied potential, gaseous atmosphere, time of treatment, geometry of the corona apparatus, post-treatment storage conditions, etc.). The matter is discussed in the light of previously published information.