Study of the nickel-based chemically modified electrode obtained by electrochemical deposition of an NiII-tetramethyl-dibenzo-tetraaza [14] annulene complex. Redox catalysis of carbohydrates in alkaline solutions. II

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

A pulsed potential-waveform displaying enhanced detection capabilities towards sulfur-containing compounds at a gold working electrode

Pulsed electrochemical detection of sulfur-containing compounds was successfully investigated by applying a four-step potential waveform at a gold working electrode. This potential waveform called APAD, which stands for activated pulsed amperometric detection, is composed of an activation potential step added to a conventional three-step potential waveform. A key advantage of the APAD at the An electrode is the ability to enhance sensitivity through the use of a short potential pulse (E-ACT = +750 mV versus Ag\AgCl and t(ACT) approximate to 90 ms) during which the formation of redox active species (presumably OH.) are able to efficiently oxidize organosulfur compounds. The APAD waveform parameters were optimized to maximize the signal-to-noise ratio (S/N) and successfully applied for the sensitive detection of lipoic acid, biotin, iminobiotin, methionine, cystine, cysteine, homocysteine, homocystine, N-acetylcysteine and glutathione, following their separations by high-performance anion-exchange chromatography (HPAEC) using alkaline mobile phases. The detection limits (S/N = 3, 10 muL injected) ranged from 0.3 for cysteine (400 pg) to 0.02 mumol/L for biotin (50 pg) and methionine (30 pg). The response of sulfur-, amine- and alcohol-based compounds was compared by using four selected pulsed potential waveforms. It was found that the APAD exhibits excellent sensitivity for thiocompounds outperforming all other pulsed potential waveforms. Ratios of the peak areas for APAD and the six-step potential integrated waveform increased from 3.2 +/- 0.4 to 13.5 +/- 0.6 for lipoic acid and biotin, respectively

Determination of Proline and Free Monosaccharides in Wine Samples by High-pH Anion-Exchange Chromatography with Pulsed Amperometric Detection (HPAEC-PAD)

A sensitive and selective analytical method for the simultaneous separation and quantitative determination of proline and free monosaccharides in wine samples by high-performance anion-exchange chromatography coupled with pulsed amperometric detection is described. Under optimized experimental conditions, a complete separation was obtained in less than 30 min, using an isocratic elution with 10 mM NaOH and 1 mM Ba(OAc)2. No postcolumn addition of strong bases to the eluent for enhancing detection sensitivity was needed. Upon 25-fold sample dilution and purification to avoid interference of tannins, pigments, and phenolic compounds, the fingerprinting of common monosaccharides (i.e., arabinose, glucose, fructose, galactose, and xylose) and proline in wines, musts, and vinegars can be easily accomplished. The method allows high recovery and satisfies the necessary requirements for accuracy, repeatability, and sensitivity. Values obtained for proline content ranged from 470 to 1190 mg/L in “Aglianico” red wines (mean value, 870 ( 192 mg/L, n ) 21) and from 168 to 286 mg/L in white wines (mean value, 208 ( 32 mg/L, n ) 11). Lower levels were found in musts of red and white grapes, 550 and 87 mg/L, respectively. The lowest content of proline, ca. 10 mg/L, was found both in white and red vinegars

Determination of Carnosine in Feed and Meat by High-pH Anion-Exchange Chromatography with Integrated Pulsed Amperometric Detection

Camosine (beta-alanyl-L-histidine) is a dipeptide regarded as an important molecular marker of the presence of processed animal proteins including meat and bone meal in animal feed. For its identification and quantification a sensitive and selective method by high-performance anion-exchange chromatography coupled with integrated pulsed amperometric detection (HPAEC-IPAD) was developed. The assay is based on isocratic elution with 100 mM NaOH as the mobile phase. Interferences of real matrices were efficiently removed; carnosine could be determined at the concentration ranges 0.1-100 muM with a rather low detection limit of 0.23 ng. Unlike feeds for dogs and cats, no carnosine peak was observed in all examined feeds for ruminants. The good analytical characteristics allowed carnosine determination down to 5 mug/g of feed

Determination of Carnosine in Feeds and Meat Samples by High-Performance Anion-Exchange Cromatography with Integrated Pulsed Amperometric Detection

Carnosine (-alanyl-l-histidine) is a dipeptide regarded as an important molecular marker of the presence of processed animal proteins including meat and bone meal in animal feed. For its identification and quantification a sensitive and selective method by high-performance anion-exchange chromatography coupled with integrated pulsed amperometric detection (HPAEC–IPAD) was developed. The assay is based on isocratic elution with 100mM NaOH as the mobile phase. Interferences of real matrices were efficiently removed; carnosine could be determined at the concentration ranges 0.1–100 uM with a rather low detection limit of 0.23 ng. Unlike feeds for dogs and cats, no carnosine peak was observed in all examined feeds for ruminants. The good analytical characteristics allowed carnosine determination down to 5 ug/g of feed

On the ability of ruthenium to stabilize polynuclear hexacyanometallate film electrodes

A novel procedure that yields extremely stable ruthenium-modified inorganic film electrodes is presented. The following prussian blue (PB) analogues were investigated: indium(III)-hexacyanoferrate (InHCF), nickel(II)-hexacyanoferrate (NiHCF), cobalt(II)-hexacyanoferrate (CoHCF), and iron(III)-hexacyanorutenate also known as ruthenium purple (RP). The process includes electrochemical film deposition and subsequent voltammetric conditioning in a Ru(III)-containing solution at pH 2. Electrochemical and spectroscopic properties of each resulting modified film are better defined, redox and switching rates improved, and stability strongly enhanced. XPS supports the conclusions that the incorporation of ruthenium imparts an extensive crosslinking between hydrate microparticles through dinuclear [Fe, Ru] oxo (-O-) and cyanide (-CN-) bridges. (C) 1998 Elsevier Science S.A. All rights reserved