Elio Desimoni

Copper dispersed into polyaniline films as an amperometric sensor in alkaline solutions of amino acids and polyhydric compounds

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.

Study of a nickel-catalysed glassy carbon electrode for detection of carbohydrates in liquid chromatography and flow injection analysis

Abstract A nickel-modified glassy carbon electrode was investigated. The nickel deposit was characterized by electrochemical techniques, x-ray photoelectron spectroscopy and scanning electron microscopy. The described electrode was tested as detector in liquid chromatography and flow-injection analysis and showed a promising combination of background current stability, catalytic activity, detection limits and reproducibility for the determination of carbohydrates in real samples.

Cobalt-based glassy carbon chemically modified electrode for constant-potential amperometric detection of carbohydrates in flow-injection analysis and liquid chromatography

Abstract A cobalt-based glassy carbon (Co/GC) chemically modified electrode (CME) is described for use as an amperometric detector in the flow analysis of mono-, di- and trisaccharides. The preparation of the electrode is very easy and rapid. As with copper- and nickel-based glassy carbon electrodes, the Co/GC CME allows the electrocatalytic oxidation of scarcely electroactive compounds without recourser to pulsed waveform potentials. Hence, constant-potential amperometric detection is feasible and it has been applied successfully to reducing and non-reducting sugars. The chemical nature of cobalt species on glassy carbon was investigated using x-ray photoelectron spectroscopy and the results indicate that a Co(III) oxide hydroxide is present on the glassy carbon surface. However, electrochemical detection in an alkaline mobile phase of aliphatic organic compounds seems to take place through mediation of Co(IV) species produced from the oxidation of Co(III) during anodic polarization. Carbohydrates and related polyhydroxy compounds were determined at the micromolar level with an operating potential of 0.50 V vs. Ag/AgCl after anion-exchange chromatographic separation. The detector responds linearly to an increase in glucose concentration with a linear dynamic range that extends over three orders of magnitude (0.5 μM-0.5 mM).

Amperometric detection of sulfur-containing compounds in alkaline media

A copper-based chemically modified glassy carbon electrode (GC-Cu) was developed to be used as an amperometric sensor for electrochemically detecting several sulfur-containing compounds in alkaline media. Under optimised flow injection conditions the calibration curves for sulfite, sulfide, thiosulfate, cysteine, cystine, etc., were linear over three orders of magnitude of concentration. Detection limits were of the order of 0.04-1.5 microM. A simple and rapid method for determining sulfite in red and white wines by anion-exchange chromatography with electrochemical detection is described.

Electrooxidation of Aliphatic Amines and Their Amperometric Detection in Flow Injection and Liquid Chromatography at a Nickel-Based Glassy Carbon Electrode

The electrocatalytic oxidation of mono- and poly-amines was investigated in alkaline solutions at a nickel-based chemically modified glassy carbon electrode. β-NiOOH exhibited electrocatalytic activity towards amines oxidation. FIA experiments were performed to test the electrode as an amperometric sensor. Under constant-potential amperometric mode (at 0.55 V vs. 4,0 M Ag/AgCl/Cl−), detection limits of all investigated analytes ranged within 1.2–3.8 pmol (S/N = 3), and the linear dynamic range extended over three orders of magnitude above the detection limits. Chromatographic separations, performed by an ion moderated partition column in alkaline solutions equipped with the Ni-CME detector, allowed very simple quantitation of aliphatic amines, avoiding tedious and time-consuming derivatization processes or postcolumn addition procedures. The Ni-CME showed good temporal stability and appreciable sensitivity.

Colloidal gold supported onto glassy carbon substrates as an amperometric sensor for carbohydrates in flow injection and liquid chromatography

Gold microparticles dispersed on glassy carbon structures were characterized by SEM. Some aspects of the electrooxidation mechanism of carbohydrates in alkaline medium were investigated by cyclic voltammetry. The chemically modified electrode described was tested in flow injection and anion-exchange LC with pulsed amperometric detection. The electrode response was stable: over 8 h a 1.5–3% signal loss was observed for all of the investigated carbohydrates. Typical relative standard deviations ranged between 0.9 and 3.5%. The detector response was linearly dependent on the concentrations of polyhydroxyl compounds and monosaccharides over three orders of magnitude. Linear plots of 1/Ip and 1/c indicated a Langmuir-type adsorption of analyte on the catalytic sites. All investigated carbohydrates were detected at the picomole level. The determination of glucose in human biological fluids was achieved by LC in an alkaline medium.

NEWDTP 2.2: A versatile system for routine XPS data acquisition and analysis

Abstract A system for X-ray photoelectron spectroscopy data acquisition and processing is described, offering a reasonable compromise between flexibility, efficiency and cost. The acquisition program was carefully designed to be user-friendly and to safely guide the operator in obtaining single or repeated multiple-region spectra. The processing program was also designed for fast and reliable operations and, besides all the usual routines, allows for spectral syntheses and differences. In particular, iterative synthesis procedures can be performed in a completely interactive environment: by this approach the chemical sense of the operator drives the iteration strategy throughout the analysis of the spectra. A few selected spectra are processed to describe software operations.

Determination of histamine by high-pH anion-exchange chromatography with electrochemical detection

Abstract 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.

Electrocatalysis and amperometric detection of ethanol at ruthenium-based inorganic films with improved response stability

Abstract A glassy carbon electrode coated with a thin film of mixed-oxidation state ruthenium oxide cross-linked with ruthenium cyanide is used for the electrocatalytic oxidation of ethanol in acidic media. This inorganic redox film offers attractive features for application as an electrocatalytic amperometric sensor in batch and flowing solutions. The ruthenium-based modified glassy carbon electrode was assembled in a thin-layer electrochemical cell, and the stability of the film was evaluated. For constant-potential amperometric detection (+ 1.05 V vs. Ag AgCl ) in flow injection analysis, substantial improvements in the response stability of the film were obtained using carrier electrolytes spiked with 5 × 10−6 M of each of the electroplating salts, i.e., RuCl3 and K4Ru(CN)6. Under optimal experimental conditions the peak current response increases linearly with ethanol over the range 0.1–10 mM; linear least squares fit of the data (n = 7) yielded a slope of 0.601 ± 0.003 μA mM−1 (95% confidence limits) with a correlation coefficient of 0.99995.

Applications of a copper-modified gold electrode for amperometric detection of polar aliphatic compounds by anion-exchange chromatography

Abstract An Au/Cu bimetallic electrode is investigated as a sensor in amperometric flow-through detection in alkaline solutions. Experimental conditions such as detection mode, pH, copper loading and flow-rate on sensitivity and stability are evaluated. Constant-potential detection at 0.550 V or 0.350 V and pulsed detection modes are tested after anion-exchange chromatography of alditols, carbohydrates and amino acids. The detection limits (S/N=3) of carbohydrates at 0.550 V and 0.350 V ranged between 4.6–9.0 pmol and 1.0–4.0 pmol, respectively. Those of amino acids were 9.0–39 pmol. In pulsed amperometric detection mode, molar sensitivities and detection limits were higher than those obtained in DC mode. Linear dynamic ranges spanned over four (alditols and carbohydrates) and three (amino acids) orders of magnitude. The Au/Cu CME retained 94–96% of its response after several hours operations in flowing streams. As an application, some alditols, carbohydrates and amino acids were determined in soluble coffee and red wine.